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Thread: Fuel mileage dropped BIG time - 82 diesel with newer 1.9 in it

  1. #1
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    May 2013
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    Fuel mileage dropped BIG time - 82 diesel with newer 1.9 in it

    Hi guys,

    My 82 diesel 1.6 was replaced with a 1.9 and was working fine. Fuel mileage mid 40's and a bit better depending on my driving. Even in winter with 20 (f)below temperatures.

    Put in new front end pieces from Parts Place here in the US. Whole new Strut/spring assembly and whole new Wheel Bearing assembly. Also new wheel bearings on the rear. None seem to be binding - as jacked up the wheels turn freely - with the front passenger side not quite as free as the drivers side.

    New drive shaft on the drivers side - but he mileage drop was there before I put it in.

    Power from the engine is fine.

    I have new Control arms and Tie Rods with ball joints yet to install. Then a new Alignment. Last Alignment they told me to do so as the right ball joint needed to be replaced.

    Tires are not wearing in any odd pattern.

    Yet, my fuel mileage has dropped in a major way. NO leaks I can find. NO one is stealing fuel when it is parked - mean dogs in the barnyard that bite intruders assure that one.

    So, I am trying to figure out why I went from 6-700 miles on a full tank to only 500.

    Maybe I did not put enough grease in when I installed the new drive shaft?
    Brakes dragging - though I can't find any evidence of it?
    Maybe the worn ball joint(s) give enough play that it hurts fuel mileage?

    Fuel is generally right at 50 Cetane, North Dakota refined diesel from the Baaken sweet Crude - supposed to be very good. I do know before the changes and mileage drop I would get better fuel mileage with it than Cenex diesel - even their summer premium blend.

    Any ideas - what may be binding or holding things back as I get going that would hit fuel mileage this big?

  2. #2
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    Is your 1.9 a TD or TDI? If a TDI it might be worth plugging in and seeing if there are any fault codes. If it's a TD it might be worth doing the timing again, have you timed it recently?

  3. #3
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    Is air cleaner due for a change?
    Are tyres the same as before?
    Might be worth having injectors spray patterns checked.
    Also injector and cam timing.
    Are you certain there no leaks on any diesel pipes? especially leak off pipes or injectors themselves. Give it a hard drive and chec under hood straight away.
    A Caddy is for life not just for Christmas

  4. #4
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    it is a regular 1.9 diesel from a 93 Jetta - an import to the US and bought from a California company who brings them in.

    I'll do a new air cleaner and see if it helps. K&N type and I keep it up - but maybe it needs to be replaced?

    Tires now summer types. Was on winter studded snows - and the loss of fuel mileage has carried over to the summer tires. At that mid low to mid 40's (mpg) even with studded snow tires and sub zero(f) temperatures.

    Have pressure cleaned the engine bay and will check diesel leakage. Don't think I have it as no diesel smell is evident.

    This really has me pulling my hair out.

  5. #5
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    Ok so a TD for sure. Has it had a timing belt recently?

  6. #6
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    The engine is a 1Y from a German Jetta bought from one of the import engine guys I found out about here.

    It runs smoothly and has good power.

    Will have it checked by a diesel shop and see about the timing.

  7. #7
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    1y engine is usually normally aspirated.
    A Caddy is for life not just for Christmas

  8. #8
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    Well spotted RNRHALL, my bad, I feel sure it is Normally Aspirated!

  9. #9
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    Not sure but I think the culprit may be motor mounts allowing the engine or transmission to shift about?

    On starting up I sometimes get a definite "clunk" as if something is shifting in the front end. It is doing it more and at times the clunk and the transmission pops out of first gear or reverse. Wondering if motor mounts worn and somehow the engine moves away from its mooring and has an effect on fuel mileage?

    In neutral, the vehicle rolls just fine. Jacked up the wheels turn without an problems and no grinding or noises. Brakes are not binding that we can tell.

    I can try new motor mounts and see if that solves the clunk and/or fuel mileage drop? So, what to be aware of in replacing the motor mounts?

    Will also get under it and check out the transmission bolts to make sure nothing is loose.

    No clutch slipping, power seems good as I can cruise at 70 without any problems.

    If anyone has experience in this area I would love to hear it so I don't start replacing stuff that is not needed.

  10. #10
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    If it's popping out of first I think that's an issue in your gearbox but it's unrelated to your miles per gallon. Have you done an mpg calculation on a recent tank to see how big the drop is?

  11. #11
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    Another thought for you, do you brim fill your tank? In the UK our petrol pumps pump faster than the tank can let out air, so you often can't hold the pump all the way down when filling, and the last 10 litres or so you have to baby it in and wait for the froth to drop.

    If I were you what you need to do is brim fill, drive a couple of hundred miles and brim fill again to work out a real MPG, if it's off then there's definitely something up

  12. #12
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    Quote Originally Posted by fuus View Post
    Another thought for you, do you brim fill your tank? In the UK our petrol pumps pump faster than the tank can let out air, so you often can't hold the pump all the way down when filling, and the last 10 litres or so you have to baby it in and wait for the froth to drop.

    If I were you what you need to do is brim fill, drive a couple of hundred miles and brim fill again to work out a real MPG, if it's off then there's definitely something up
    Have been driving and filling for a few decades now and I can top it off with the "dribble system" - dribbling into the tank til it is showing at the cap level - taking 10 minutes or so at times to do so due to foaming. The tank is full when I do that.

    Have lost between 13-15 mpg in driving. Rolls just fine. Not running rough. Maybe it "is" timing but would seem to me that the engine would not be quite as smooth and power would be a bit off if that were the case.

    The "clunk" in the front has been there on and off for a few months. I have tried tracking it down. Thought maybe Brakes or somehow the wheel assembly, but no play when I try push and pull on it. The problem if starting to go and then popping out of first and reverse is newer and accompanied by the clunk noise as if something in the front end or engine bay is shifting/moving. That is why I am concerned a motor mount may be working loose or worn out somehow.

    A drive shaft and/or bearing would not clunk like this. Also should make noise when I turn tightly one way or the other. Is not happening. I don't think it is a broken strut as there is no lean to the truck to either side.

    So - looking for help on this one.

    I have new motor mounts, new tie rods and ball joints and new Control arms to put in. But I don't think they would be a reason for a Clunk in the front.

    So, any other suggestions? I can do mechanical work - just older and slow on it these days. If it gets too complicated I let a shop do it - same with electrical. But taking it slow I can replace most things. Glad for Auto Mechanics class in the 60's in High School and our owning a service station back then.

  13. #13
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    Pop the bonnet and get someone to watch the engine whilst you engage and disengage the clutch a couple of times. If the engine movement is substantial then new mounts are definitely a good idea.

    Quoting google here:
    "Popping out of gear is a common problem when it comes to manual transmissions. The most common reason a manual transmission would jump out of gear is due to low or contaminated fluid, worn synchronizers inside the transmission, or improperly adjusted shift linkage."

    When the car pops out of gear it will push your gearstick via the linkage, which would explain your movement / shifting in the engine bay. Have you checked your transmission fluid recently? If the problem has developed recently I would guess it's unlikely to be the shift linkage

  14. #14
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    If the rear "dog bone" engine mount has failed this would cause the knocking and will progressively get worse, best way to check is to rock the engine from underneath (be careful if you do this from axle stands, not always easy to tell from the top of the bay, I don't know what linkage you have but if its rod change it will most definetly pull it out of gear, if cable then possible not so much but that all depends on how much movement you have.

  15. #15
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    Any luck Deardorff?

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