Questions around Diesel Cars (Experts Only)

frostman on 21/05/2019 - 09:37

I know this isn't CarAdvice forum or anything, but just looking for (expert/SME) advice on Diesel Cars from people that have owned or own Diesel cars.

So went to the dealer to look at the CX8 (diesel) vs CX9, obviously the additional Torque of the diesel CX8 (and less weight) got my preference between the 2.

However the car dealer asked me how many Ks I do, I estimated ~13,000/year, he said not good enough for a diesel, needs 15,000-20,000 else I would not cut it for the diesel benefits.

Further chatting, he said if you actually do under 15Ks/year you will find yourself out of pocket as the diesel filter will likely clog up earlier due to less use and cost around $5,000 to replace.

My question is, how often do you need to replace it on a brand new car, is the advice above sound or fiction?

Automotive

Comments

  • Skramit on 21/05/2019 - 09:48
    +6

    It's good advice. For the DPF to self-clean properly by burning off the collected soot, you need to be putting the car through longer runs occasionally, not just city short trips.

    • [Deactivated] on 21/05/2019 - 12:20

      Was it Spackbace?

    • brendanm on 21/05/2019 - 12:50
      +7

      Number of KMs a year is completely irrelevant. It's the length of the individual trip that matters, just needs to get everything up to temp every once in a while.

      • Skramit on 21/05/2019 - 12:53
        +1

        Agreed….. but number of KMs per year is usually a good indicator if the driver does many long runs or not to get the exhaust up to temp. It's a simplification in order to make a best guess.

        • brendanm on 21/05/2019 - 12:56

          Not really, question should be more like "do you do highway driving at least once it twice a week". Some cars care more about this than others.

          Mazda have a bad history with diesels with dpfs, and diluting the fuel with diesel due to their burn off process. Not sure why they have so many issues with it.

          • Skramit on 21/05/2019 - 13:00
            +1

            @brendanm: Agreed.

            I'm just defending the overly simple line of questioning by the dealer. It is still useful.

            And it also helps determine if there's a cost advantage for the fuel, as KM/year is relevant for that.

      • paulh1977 on 28/04/2021 - 11:14

        you are completely correct, its all about running the engine and exhaust up to high temps that will allow the DPF to work effectively. If you dont do this often enough the DPF will clog up and you will get warning lights popping up on your dash. ODB scan will probably point to DPF which will either need cleaned or replaced and both options are not cheap. Good long motorway runs once a month allows the car to blow all the soot off, any also punching it off the line from time to time is good to blow any excess soot out of the pipes. I am from ireland were every other car is diesel and dpf problems are pretty common.

        • Euphemistic on 28/04/2021 - 12:09
          +1

          punching it off the line from time to time is good to blow any excess soot out of the pipes

          Punching it off the line is a good way to overfuel and create excess spot - which will probably contribute to blocking things up.

  • Changskies on 21/05/2019 - 09:55
    +1

    This dealer is good.

    • GG57 on 21/05/2019 - 10:04

      I agree, but to be honest I have been provided with that same information by Subaru, Peugeot and Citroen dealers over the years.

    • John Kimble on 21/05/2019 - 11:46
      +1

      Not really

  • josetann on 21/05/2019 - 10:05
    +3

    Per the filter, it's not so much total mileage as it is city vs highway miles. It'd be better to put 10K a year on the car with purely highway miles than 20K a year in stop and go city traffic.

  • maybeamacy on 21/05/2019 - 10:06
    +3

    Mazda aren't well know for making reliable diesel engines: https://forums.whirlpool.net.au/thread/36rx5863

    A bunch of people on WP have had their diesel CX5 engine seized requiring new engine replacements (which Mazda are mostly doing under goodwill to be fair).

    • frostman on 21/05/2019 - 10:07

      Thanks man, that's probably one point to consider

    • slknv on 21/05/2019 - 10:12

      Agreed, pretty well known in the cx-5 community to avoid diesels.

    • [Deactivated] on 21/05/2019 - 10:39
      +2

      Stay away from Mazda diesel. The salesman is doing you a favour.

      Just realised I'm not an expert

      • frostman on 21/05/2019 - 11:00

        I know you're taking the piss, but what I meant by expert is someone providing sound knowledge based on first-hand experience.

  • [Deactivated] on 21/05/2019 - 10:54
    +3

    i'm an expert

    • pegaxs on 21/05/2019 - 12:15

      X being an "unknown quantity", spurt being "a drip under pressure". :P

      • l005e on 21/05/2019 - 12:21

        Omg you sound just like my dad

      • Ozpit on 22/05/2019 - 10:13

        Is that you dad?

      • [Deactivated] on 28/08/2019 - 14:40

        I thought X was a "has been", spurt "a drip under pressure".

  • altomic on 21/05/2019 - 11:20
    +1

    I have a 2013 automatic diesel outlander.

    the air intake pipe cracked somehow about 12 months ago

    it caused an issue with air intake filter.

    car went in to limp mode and was smoky.

    got a replacement pipe fitted.

    DPF was reset.

    car was better but was still very smoky.

    used some injector cleaner.

    seemed to fix the problem. somewhat.

    but now still smokey at times.

    I can start off from the lights and it will smoke but then if I drop it in to a lower gear then the smoke stops.

    could be the exhaust gas recirculation (EGR) or could be the Diesel Particle Filter (DPF) .

    I'm considering cleaning out the EGR and manifold as crap can collect there.

    I also think the turbo may have died.

    up until the air intake pipe cracked it had been a fine vehicle.

    unless you do regular trips at a constant speed (e.g. 20 minutes @ 100km/h) then your DPF won't get the clean out it needs. - as Josetann says above.

    • frostman on 21/05/2019 - 11:30

      thanks, not sure I can do this weekly/fortnightly.

      I can hit up a trip to the city say (15-20km) every weekend but with plenty of stopping and traffic!

    • pegaxs on 21/05/2019 - 12:13
      +6

      @altomic; Have you been taking post formatting lessons from IVI???

      • altomic on 21/05/2019 - 13:07

        no, i was going for a poetic format

        • Ozpit on 22/05/2019 - 10:22

          I sensed the rhythm in the syntax, but see if you can throw in a few rhymes next time.

    • MechEng on 22/06/2020 - 07:35

      This can be caused by dirt getting into the turbo. I assume the crack was after the air filter.
      Get your turbo check as it can become very expensive very quickly, think repair turbo vs change turbo.
      Good luck

  • Happy501 on 21/05/2019 - 12:01
    -1

    If you have a new diesel then you will need to do a long highway drive weekly, if not fortnightly, else you will clog up the manifold which cannot be replaced like a normal filter.

    Electronic cleaning and other gimmicks don't do much, if anything.

    Only thing to do is take the engine apart and spend half a day with a massive tub and the right chemicals to get the gunk out.

    • frostman on 21/05/2019 - 12:42

      screw that…im out

    • brendanm on 21/05/2019 - 12:52
      +1

      Take the engine apart? The dpf is not in the engine, it is in the exhaust after the turbo.

      You can do a forced regen through a scan tool.

      • Euphemistic on 22/05/2019 - 08:15
        +2

        Maybe referring to the EGR system. That is exhaust gas recirculating or something, oily gasses fed back through the system to burn off the excess before it is sort out the back. Can clog up ge system and require removing the manifold and cleaning it out.

        • brendanm on 22/05/2019 - 22:07
          +1

          The gases aren't oily. The soot mixes with the oil mist from the pcv system and makes a horrid paste. Has nothing at all to do with length of drives, and doesn't burn off. It happens no matter how you drive, and happens with direct injection petrol engines as well.

          • Euphemistic on 23/05/2019 - 00:02

            @brendanm: Thanks. Happy to be educatief soms more in how diesel engines work.

          • Happy501 on 26/05/2019 - 19:21

            @brendanm: you have no idea what you are talking about. I hope to god you are not a mechanic

        • Happy501 on 26/05/2019 - 19:23

          Thats exactly it mate, The gasses may convert to liquid, which then may solidify and remain after a "weak" burn.

  • pegaxs on 21/05/2019 - 12:04
    +3

    Diesel Cars (Experts Only)

    Damn. Counts me out… I only work on diesel trucks.

    Dealer is semi right. If you are doing low KM per year, the time it takes for the diesel to pay for itself takes longer. I imagine there is a $x,000 premium to buy a diesel. So your fuel savings from buying a diesel would take on average 150,000+km to break even… (or about 10~12 years are your rate.)

    As for DPF, if you live in the city and drive short distances every day, don't buy a diesel. For a DPF to work, it needs to get hot, reeeeealy hot. The only way to do this is to run it on a freeway from time to time. Most people have bad experiences with DPF because they live in the city and never get to highway speeds on a regular enough basis.

    Short of it is, if you live and/or do most of your driving in a city from home to the CBD in peak hour snarl, buy the petrol or hybrid if that option is available.

    If you live in a rural area and it's a 40min trip to work on a quiet highway, go nuts and get a diesel…

    • frostman on 21/05/2019 - 12:44

      Thanks for the tip, and yes Truck experts included haha

    • Ozpit on 22/05/2019 - 10:33

      Thrashing (high revving) a diesel by staying in lower gears (in manual mode) gets the temp up quickly. That’s my fortnightly method.

      • pegaxs on 22/05/2019 - 12:08
        +1

        Meh. If that's what works for you and your car is happy that your doing that to it, have at it. My preference is to just get out on a highway every now and then. Much easier on the components than "thrashing"…

        • Ozpit on 24/05/2019 - 12:56

          By 'thrashing' I meant instead of freeway cruising in top gear (7th), I use fifth or fourth. I often find that when cruising in 7th, the engine/oil temp (NOT coolant temp) as shown on the dash gauge doesn't rise above high 80s/low 90s Centigrade, which is often around the same temp as when I'm 'stop and going' in the suburbs.

          As I understand it, the idea of freeway driving a diesel is to bring the engine temp up high enough for the exhaust gasses to clean out the dpf (I'm assuming the much higher exhaust gas temp also increases as the engine temp increases). And my experience is that cruising in 4th or 5th quickly brings the engine temp up around 100 C. And I might keep this up for 15 minutes or so.

          Engine speed at 100 kph in 7th is around 1750 rpm; in 4th it's (from memory) around 2750 rpm.

          I guess the question is: what's the ideal minimum engine temp for the dpf to get a 'proper' clean out. I don't know. But bringing the engine temp up to around 100 C gives me more confidence that the dpf is getting a better chance to be cleaned out - and in shorter travel time - than an engine temp of around 90 C.

          In any case, I doubt that maintaining the motor at these higher revs once a fortnight is in any way detrimental to the motor or transmission (it doesn't redline until 5000 rpm). Nor is it harmful to bring the engine temp up to 100 C. So where's the harm, apart from using a little more fuel?

          Of course, I'm happy to be corrected on any/all of this, and welcome any thoughts.

          • brendanm on 24/05/2019 - 14:06

            @Ozpit: Exhaust gas temp increases with engine load. More fuel= more heat

          • Euphemistic on 24/05/2019 - 17:56

            @Ozpit: The DPF requires a ‘burn’ to clean. Once to temperature the system injects fuel into the DPF to promote the burn.

            We had a Captiva (I know, learned about that). It mostly drove around town and the only time the DPF light came on was after a 1hr drive of mostly freeway every couple of months. The light would come on almost every time after we got back into the car after lunch etc. and we’re starting off driving back home. Never saw the light other than that so I assume it was not required very much or was carrying it out around town.

  • Cluster on 21/05/2019 - 12:16
    +2

    The salesperson is doing a good job (shocking I know, first time for everything). Someone who doesn't travel long distances (20km+, at 80km/h or more) regularly should not get a diesel due to the risk of the DPF not regenerating correctly. Subaru dealers even get diesel buyers to sign a document stating they understand this and will travel at higher speeds on a regular basis. Just driving short distances around the suburbs at 50km/h is asking for trouble in a modern diesel.

    Having said that, beware of salespeople rubbishing their own product, the diesel in this case. It may be the case that the dealer doesn't have the diesel in stock but has petrol, therefore their #1 job is to sell what the dealership has already bought by any means necessary.

    I experienced this buying a Hyundai i30 diesel. I wanted to test drive one. Dealership didn't have any. After test driving the petrol model the dealer started coming up with all sorts of excuses to get me to buy a petrol right there and then.

    Me: "I would still like to drive the diesel version and compare the two"

    Salesman: "Well… the servicing costs for the diesel are higher"

    Me: "How much by?

    He shows me a schedule of service costs. It's $40 extra per 15,000km.

    Me: "That's fine, I'm happy to pay that"

    Salesman notices his tactic isn't working. Tries something desperate.

    "Well… the service department tells me the diesels (due to the less refined fuel) require more frequent fuel filter changes"

    I didn't believe his BS and went to a nearby town to buy a diesel i30. 80,000km later and it's running like clockwork and has yet to have all those mega expensive fuel filter changes.

    I bet now dealerships try to scare buyers with the DPF and saying how many thousands of dollars it's going to cost.

    • Ozpit on 22/05/2019 - 10:42

      I love the low-down torque of a diesel. And the hill climbing grunt when fully loaded is wonderful, especially when compared with the petrol version of the same vehicle.

  • askme69 on 21/05/2019 - 15:02

    Quick run on the HWY will burn the DPF, or your car will tell you that it needs it. You then do a HWY run and it dumps fuel and burns.

    This is with VAG stuff, Don't know about Japanese cars.

  • tight-ass on 21/05/2019 - 22:44

    We have a CX9 (2.5Lt turbo AWD Azami) that we purchased new in 2017. The car was serviced yesterday & the loan car was a new CX8 Asaki (diesel AWD).

    I honestly thought the CX8 had less torque than the CX9 after driving it all day yesterday - it certainly seemed like it.

    The CX9 AWD can get mid 7L's per 100 with very careful driving, but I generally have a heavy right foot and get around 9-10L's per 100. For such a large car they are surprisingly quick (0-100km/h in 7s)

    • frostman on 22/05/2019 - 09:50

      , but I generally have a heavy right foot and get around 9-10L's per 10

      Really?

      My CX5 GT (non turbo) is AVG at 12.1L/100 Ks, I must be driving it with a heavier foot.
      9-10/100 on a CX9 is very good!

      I'm actually considering the Klugar 2019 over the CX9 for now, despite the Klugar interior dash looking like that of a 2005 Toyota Hilux

      • [Deactivated] on 22/05/2019 - 17:08

        Why not one of the new RAV4 Hybrids if you're thinking about a Kluger? Not much size difference, much better car.

      • Peace Maker on 23/05/2019 - 06:18

        Kluger is on run out because a new hybrid version is coming.

        • frostman on 23/05/2019 - 11:13

          Really?

          I saw a Car Advice brochure before the new 2019 Klugar was launched suggesting the RRP is $57K and now looked at the toyota website and it's $59K for the GXL, if anything prices increased

      • tight-ass on 23/05/2019 - 09:17

        Yep some people are even managing to get their CX9 into the mid 6's - that obviously involves some long distance driving and a very light foot, but very impressive considering it's size and weight

  • mikey13b on 22/05/2019 - 07:39

    So would a DPF removal take away this issue of diesels not being good for city driving?

    • pegaxs on 22/05/2019 - 08:01
      +1

      DPF removal isn’t that easy, but they can be deleted. The problem is, if you get found to have deleted it and this gets back to the EPA, you could get a hefty fine. That being said, the chances of being caught is not that great if your car is out of warranty and you are on good terms with your mechanic.

      Deleting the DPF would be better for the car, but not better for the city. The black soot carbon particles it is designed to catch and burn off will no longer be caught and just released into the environment instead. So, while it may make your car less maintenance taxing, it would be a pretty dick move to everyone else that likes breathing air.

      The thing is, if you live in the city and you do a majority of your driving in the city and/or you don’t do a lot of km/year or you don’t tow anything, there is no real benefit to owning a diesel, and will probably end up costing a lot more in the long run.

      • whooah1979 on 22/05/2019 - 19:26
        +1

        OP could get an older used SUV that doesn't have a DPF.

        • pegaxs on 22/05/2019 - 19:39

          This is what I usually recommend to people looking at buying a diesel and living in the city. But if people are looking at buying new and I think their driving habits would kill a DPF, I would not recommend they buy a diesel.

  • ozbargainoid on 22/05/2019 - 07:53
    +2

    Diesel exhaust particulates are a known carcinogen. So it depends how much you care about you fellow citizens if you decide to remove the DPF.

  • reactor-au on 22/05/2019 - 09:33
    -3

    It's just easier NOT having a diesel. Petrol is more consistent, a diesel feels new for the first 3,000km after a oil change then it feels old again. I won't get another one unless I move to regional.

    • frostman on 22/05/2019 - 09:49

      thanks

    • brendanm on 22/05/2019 - 11:36
      +3

      Blatantly false

      • pegaxs on 22/05/2019 - 12:06
        +2

        I agree. It's right up there with "I don't like diesels. They just feel like old trucks to drive…"

        • reactor-au on 23/05/2019 - 08:59
          -1

          Exactly, 3,000km after a service they feel like an old truck again

          • pegaxs on 23/05/2019 - 10:05

            @reactor-au: Oh, totally. What we do as mechanics is, at the 3000km service, we take your engine out and replace it with an old John Deere tractor engine and use your engine in our tractors.

          • brendanm on 23/05/2019 - 10:08
            +1

            @reactor-au: Yes, the age of the oil is directly proportional to the power/torque of the engine. Thank you for letting us know.

  • [Deactivated] on 22/05/2019 - 12:00
    +1

    Not diesel related but the CX9 has a reputation for having unreliable electrics, particularly the power windows.
    This is first hand experience.
    Try typing Mazda CX9 into Google search and see what pops up!

  • jonkvh on 22/05/2019 - 17:01
    -4

    2 things. Never buy Mazda, they aren't long term ownership cars. Modern electronic/diesels are also not long term ownership vehicles. Wait until you start hitting 200,000kms, diesel repair bills are horrendous. You have to be really fussy with servicing owning a diesel anyway. I've had to recondition my diesel pump, $3000. The engine brand new off the rack is worth $8000 fitted.

    • brendanm on 22/05/2019 - 22:10
      +2

      Plenty of common rail and pd diesels with much more than 200k km on them. Not sure what magical car you have that requires a $3000 high pressure pump rebuild, they are generally around $1500 brand new. $8000 for a brand new diesel fitted is very cheap.

      I believe you are just pulling numbers from where the sun doesn't shine.

      • jonkvh on 23/06/2020 - 08:46

        "I believe you are just pulling numbers from where the sun doesn't shine." Really!? The pump, injectors and new filter plus glow plugs, no one does just the pump.

        This was one of two diesel Hilux's, both 30 years old, bought as a fleet sale.

        Talk to a diesel pump specialist, the modern one's don't hold up well at all, in any model range.

        • brendanm on 23/06/2020 - 08:52
          +1

          Wow, I happen to be a qualified diesel tech. You said pump, not pump, injectors etc. There are plenty of modern ones that hold up very well.

          • jonkvh on 24/06/2020 - 08:32

            @brendanm: Here's the thing, my old man is a diesel mechanic, who was completely effing useless in the whole process/made shit worse with his so called 'expertise'. And you don't think I didn't discuss this with the Diesel Injection Specialist? Or the finicky nature of modern diesel injection systems?… maybe get rid of the old Hilux.

            I got incredible help from the technician, knowledge wise. Since he understood what my position was.

    • Kandrew on 22/05/2019 - 23:32

      I'm not going to argue with your 'Never buy Mazda.' statements

      However, I will argue your points about modern diesel engines. Both of my Peugeot diesel-engined cars have well over 200 000 km on the odometer. The 1999 model 406 has over 585 000 km, and the 2006 model 307 has just short of 310 000 km.

      Yes, I did have to have the Bosch injection pump on the 406 reconditioned not long after I purchased the car with 350 000 km. But the car had had no fuel cap on it when I purchased it, and the person who did the reconditioning said that he found evidence of water in the pump. I'm trying hard to think of any other major engine repairs.

      I'll certainly go again with a Peugeot diesel engine, but my driving warrants it. Each car does more than 25 000 km per year, and very few of those kilometres are trips under 40 kilometres. And because I'm driving mostly between country towns, my speeds are mostly from 80 km/h to 100 km/h.

  • Euphemistic on 22/05/2019 - 17:33

    Diesel price is more consistent, petrol fluctuates in cycles.

  • Daniel Plainview on 25/05/2019 - 10:18

    Good post, excellent info in it.

    I live rural and had been leaning towards a small diesel for our daily commute (19km each way, mainly 80km/hr zone) - and thought this would be adequate to have the DPF passively clean itself. Seems this wouldn't be enough and it'd have to use 'active' cleans to remove buildup. Which is a bit of a bummer and somewhat detracts from the edge over a petrol vehicle.

    • brendanm on 26/05/2019 - 08:07

      You could 100% use a diesel.

      • Daniel Plainview on 26/05/2019 - 12:29

        I appreciate your reply.

        I know I 'could' use one - but it seems from the info I've read the commute isn't likely to passively generate high enough temps in the exhaust to clean the DPF - therefore the car would have to activate the 'active' clean cycle - where it uses additional fuel to make the exhaust hotter.

        If this is wrong happy to be corrected but everything I've read seems to indicate longer & higher speed trips are needed for passive cleans. :-)

        • brendanm on 26/05/2019 - 12:43

          My Passat did similar driving for a year with zero issues, averages high 5l per 100. I'm about to buy another dpf equipped car to do 15km each way runs to work, 80km zone max. I'm a mechanic and not worried about it at all, but in the end it's up to you. Diesels have saved me a lot of money in fuel, and they are nicer to drive.

          • Daniel Plainview on 26/05/2019 - 16:43

            @brendanm: No look its good info to have - especially given your profession - so appreciate you sharing.

            That said I would suspect your VW is running active cleaning cycles to maintain the DPF - which isn't the end of the world and not sure what impact that has on fuel usage vs not doing so - likely very marginal.

            So you're 100% correct in that I could use a diesel - and look I love them on many levels - but given the premium they seem to be priced at - and that I'll likely be buying 2nd hand (and from what I've read and can deduce it's a bit of a false economy for 2nd hand buying modern diesels with high mileage or quite a few yrs on them - in that the later higher maintenance costs (than a petrol) land with you.

            My area (Coffs Harbour) is very odd with its petrol vs diesel pricing - they'll always be very similar - they tend to rort/collude on ULP pricing. So using ~1/3 less fuel (on paper specs, which should plus up the same %) vs ULP is a big advantage. So I'll run the ruler over them again as while my commute isn't ideal diesel territory its not something that should preclude them.

            • brendanm on 26/05/2019 - 19:46

              @Daniel Plainview: Whether it's active or passive doesn't bother me as the fuel economy is great. There's no reason that egts can't be high enough at 80kmh for passive regen, back the boost off a bit and egts will rise, I'm sure the manufactures have thought of this. Might have to have a look at what egts are like on it one day.

              The problems arise when you don't drive far enough to even get an active burn done, then you end up with a clogged dpf, and do forced regens.

  • frostman on 25/05/2019 - 21:19

    Well im stuffed then:

    CX-9: Great features but is a boat of a car (over 5M length)
    CX-8: Perfect size. great all round, as above its diesel
    Pathfinder: Great interior and technology, crappy 1990 shape
    Kluger: Great shape, great engine, interior is the same as a 1999 Klugar, even folding mirrors arnt available

    • brendanm on 26/05/2019 - 08:08

      Pathfinder 1990 shape? Been to Specsavers?
      Kluger interior same as 1999? See above.

  • wixy on 29/08/2019 - 14:15

    Try looking for a petrol 7 or 5+2 seater with no cvt. Struggle town!

    Getting a santa fe highlander only because they reputedly do not have dpf issues (dpf heats up even on short trips) but I'm still very nervous..

    • Euphemistic on 29/08/2019 - 16:41

      As much as there are plenty of warninnof things going wrong, there are plenty that just get driven daily with no issues. If it was really the end of the world like some people suggest you wouldn’t be able to sell one that is a few years old No one would buy them because they weren’t running.

      If you are eally concerned have a look around and see how many of what you are interested in are still driving.

      Of course there are specific models to avoid (Captiva is first on the list)

  • chumlee on 29/08/2019 - 16:43

    Im an ex perv if that matters

    chumlee on 29/08/2019 - 16:43 (Collapsed - Offtopic. Show)
    • Euphemistic on 30/08/2019 - 06:23

      Was it the chafing on the ankle bracelet that cured you?

  • dennycrane on 20/04/2021 - 21:07

    Sorry to revisit an old thread but OP, what did you go with and are you happy? I’m in the exact same predicament trying to choose between CX8 diesel and CX9.

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