Chevy .65L Duramax Diesel Problem

Discussion in 'Trucks and Trailers' started by SLC LLC, Aug 31, 2008.

  1. SLC  LLC

    SLC LLC LawnSite Senior Member
    Messages: 667

    Looking for anyone with knowledge on the Chevy 6.5L Duramax Diesel. I have a 2004 2500hd that I bought used last December. It only had like 50,000 miles on it when I bought it. When I hit 55,000 miles - I changed the oil. After I did this, I noticed that my oil pressure gauge started to act like a tachometer. When my RPM's went down, so did the oil pressure gauge. When the RPM's went up, so did the oil pressure gauge.
    I spoke with my mechanic, who is not a specialist in diesels. The problem is that there are no diesel mechanics in this area that I am aware of other than the dealer. We both agree that this is not correct, but cannot figure out why this is happening.
    We have done the following things in troubleshooting:

    1. Changed oil filter again.
    2. Replaced the sending unit
    3. Changed the oil to Delvic 15-40 (as we were told by the dealer that this is the specific brand used in chevy)
  2. IA_James

    IA_James LawnSite Silver Member
    from Iowa
    Messages: 2,592

    That's what should happen. The problem is you have an actual oil pressure gauge, as opposed to the "idiot light with a stick" like many new vehicles. Spin the engine faster, the oil pump goes faster. There is only a limited amount of space in the galleys and passages, so oil pressure increases. As long as you're carrying about 10 psi per thousand RPM, you're good to go.
  3. Milwaukee

    Milwaukee LawnSite Member
    Messages: 144

    What oil filter you use? Fram?

    I have see that due gunk in passage get slow then sudden clog then oil pressure go raise little then try push finally it out. It happened on Ford 300 and Chevy 350 that never run hot enough most short drive for several years.

    Do you see oil get dirty short time like sludge?
  4. SLC  LLC

    SLC LLC LawnSite Senior Member
    Messages: 667

    There is a pretty good fluctuation in the oil pressure gauge. I am not questioing you, just trying to explain what is going on. I am trying to avoid the damn dealer because I know that will cost a fortune. The thing that concerns me is that it did not do this before I changed the oil.

    I use Wix filters. No, the oil does not seem to be producing sludge. I change every 5000 miles. Was using Rotella oil before the mechanic switched brands.
  5. Milwaukee

    Milwaukee LawnSite Member
    Messages: 144

    You mean when you stop at light engine idle at 650 rpm so oil pressure go down like middle when you touch pedal to go did oil pressure go high?

    My 79 F150 alway do that if I stop it 15 psi at 600 rpm but go to 45 mph at 1,850 rpm oil pressure is 35 to 40 psi. it been do that when I switch to 15w40 diesel oil since 5w30 oil make worst it get 0 to 5 psi during hot run. Keep mind it have 327,100 miles now it still use everyday but not now we are still work on fuel system.
  6. IA_James

    IA_James LawnSite Silver Member
    from Iowa
    Messages: 2,592

    That's odd that it wasn't doing it before. Honestly though, if it was my truck, as long as I had over 10 psi per thousand RPM, I wouldn't sweat it. What are the hi/lo readings on your gauge? What does it seem to operate at most of the time?

    FIRESCOOBY LawnSite Senior Member
    Messages: 986

    First, the motor you have is a 6.6 Duramax, the 6.5 was the former GM Diesel.

    Secondly, my Duramax (as well as every other vehicle) does that. The oil pressure will be fairly high first thing in the morning. After that the oil pressure will fluctuate with RPM's (engine load).
  8. 02DURAMAX

    02DURAMAX LawnSite Gold Member
    Messages: 3,801

    Exactly...You need to pay more attention on your trucks!
  9. TXNSLighting

    TXNSLighting LawnSite Fanatic
    from DFW, TX
    Messages: 6,464

    your 6.6! Duramax is normal. Nothing wrong with it there.
  10. SLC  LLC

    SLC LLC LawnSite Senior Member
    Messages: 667

    Sorry, our 2000 Chevy Diesel is a 6.5L, got them mixed up. The 2004 is a 6.6L.

Share This Page