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Thread: Engine temperature running hotter than usual

  1. #1
    Senior Member 82DMC12's Avatar
    Join Date:  May 2011

    Location:  Olathe, KS

    Posts:    1,103

    My VIN:    11596

    Engine temperature running hotter than usual

    A bit of background story - in December 2021 I was driving my DeLorean to work and suffered a split hose between the water pump and passenger side head. During this incident the temp gauge briefly hit the 240F mark before I was able to safely get the car out of traffic and into a parking lot. Once I got the car home, I let it sit for a day and then drained the oil to make sure there was no coolant in it. There was absolutely no sign of antifreeze in the oil, and my plastic oil filler screen was fine so I figured I dodged a bullet regarding overheating. I decided it was time to replace all the coolant hoses in the engine compartment for the second time of my ownership (last time was probably 15 years ago). This of course spiraled into other projects while I was in the valley and etc etc and today my car is finally 100% working once again.

    The coolant system was actually done a couple months ago but I haven't driven the car much at all since then because I was getting my angle drive rebuilt. So, I had already bled everything a couple times and thought all was well. Angle drive is back in tonight and I went for a long-awaited test drive.

    Unfortunately I am finding that my temp gauge, after about 20 to 30 minutes of mixed residential and highway driving, is reading about 215F which is a fair amount higher than it ever used to be for the previous 20 years of my ownership. I used to always sit just above the quarter (160F) mark. My fans are both on but they aren't really doing much to drop the temperature. They are coming on probably around 175F just like before. It's getting just below 220F and even sitting idle, hot, fans and A/C on, it's not on 220F but not falling much either.

    A couple other observations and comments -

    1) No white smoke or anything like that from the exhaust
    2) No odor of coolant while running
    3) I checked the overflow tank a couple days ago and the level was about half, maybe slightly below half, full.
    4) New 15 PSI radiator cap from DMCMW
    5) I have a continuously bleeding radiator housing (DPNW) that returns to the overflow and have had that forever
    6) New DPI radiator bleeder kit - I bled the radiator again while it was just below 220F and some air and steam came out so I think it's finally REALLY bled, but I went for another drive after that and no improvement
    7) Coolant replaced with fresh 50/50 green during my valley overhaul
    Before putting the intake on I rented a cooling system pressure tester from Autozone and I was holding pressure after finding a few small hose clamp leaks.
    9) New thermostat and gasket installed from DMCMW
    10) Ever since my valley rebuild was done, I seem to be burping a couple ounces of coolant out of the overflow tank hose about the time I pull into my garage after a drive. At first I thought my overflow tank was too full (I filled it to about 3/4 full initially) and I was hoping this burping would stop once it found the right level but now I'm worried it's a sign of something else.

    What should be my next steps to diagnose this problem? Here's a picture I took before pulling the car into the garage for the night. Incidentally, my volt gauge does read lower than actual alternator output (actually measuring 13.4V with a multimeter in the engine bay) but it's been doing that since before the cooling system issue.

    PXL_20220513_012931060.jpg
    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

  2. #2
    Senior Member 82DMC12's Avatar
    Join Date:  May 2011

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    The car has been sitting for about 90 minutes now and I was able to remove the overflow cap to check coolant level and condition. It's about 3/4 full and green and clean.

    PXL_20220513_030153727.jpg
    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

  3. #3
    Senior Member Bitsyncmaster's Avatar
    Join Date:  May 2011

    Location:  Leonardtown, MD

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    My VIN:    03572

    Did you replace the sender going to the temp gauge or the thermostat? I would not think any other valley work would have changed the engine temp setting.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  4. #4
    Senior Member
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    Never overlook the obvious. Is the water pump belt tight?
    Ron

  5. #5
    Senior Member
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    Did you change out the otterstat too? I know some of the new ones are calibrated to a different on/off temperature (i.e. higher than the old ones). Might be a new calibration on the thermostats too?

    You said the cooling fans up front are turning on at the same temperature they always used to? 175 deg F? Have you stuck your head under there (carefully, lol) and confirmed both fans are working/turning?


    Sept. 81, auto, black interior

  6. #6
    Senior Member
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    Quote Originally Posted by Bitsyncmaster View Post
    Did you replace the sender going to the temp gauge or the thermostat? I would not think any other valley work would have changed the engine temp setting.
    x2 on this, I replaced the temp sender with a newer one during the engine rebuild and it read higher. I ended up refitting the old unit, I couldn't relax with the gauge reading around 220 (even though I verified it was fine with a laser thermometer)

  7. #7
    Senior Member 82DMC12's Avatar
    Join Date:  May 2011

    Location:  Olathe, KS

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    Quote Originally Posted by Bitsyncmaster View Post
    Did you replace the sender going to the temp gauge or the thermostat? I would not think any other valley work would have changed the engine temp setting.
    No, I did not replace the temp sender but I did replace the thermostat. The thermostat came from DMCMW. I actually didn't even touch or remove the temp sender.

    Sent from my Pixel 3a using Tapatalk
    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

  8. #8
    Senior Member 82DMC12's Avatar
    Join Date:  May 2011

    Location:  Olathe, KS

    Posts:    1,103

    My VIN:    11596

    Quote Originally Posted by DMC-Ron View Post
    Never overlook the obvious. Is the water pump belt tight?
    Ron
    New belt! And yes it's correctly tightened. I had the water pump out during all that work and it looked good, no obvious issues.

    Sent from my Pixel 3a using Tapatalk
    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

  9. #9
    Senior Member 82DMC12's Avatar
    Join Date:  May 2011

    Location:  Olathe, KS

    Posts:    1,103

    My VIN:    11596

    Quote Originally Posted by Jonathan View Post
    Did you change out the otterstat too? I know some of the new ones are calibrated to a different on/off temperature (i.e. higher than the old ones). Might be a new calibration on the thermostats too?

    You said the cooling fans up front are turning on at the same temperature they always used to? 175 deg F? Have you stuck your head under there (carefully, lol) and confirmed both fans are working/turning?
    I did not replace the otterstat. The fans are coming on around 175F which is, I think, the same range they always have. In the past, the fans would come on and cool until the needle dropped down to about the 160 F mark, then cycle between 175 and 160.

    I did crawl under there and I could feel air moving behind each fan but didn't visually confirm each blade turning, I'll do that too but I'm quite sure the "wave of the hand" was a good test.

    Sent from my Pixel 3a using Tapatalk
    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

  10. #10
    Senior Member 82DMC12's Avatar
    Join Date:  May 2011

    Location:  Olathe, KS

    Posts:    1,103

    My VIN:    11596

    Thinking a bit more about this. Due to this history and possibility of an overheat, I want to rule out head gasket leaks completely. Would these two tests be sufficient to be sure the head gaskets are fine?

    1) Now that I have about 75 miles on the car since the hose split, I can drain the oil one more time and check for coolant in the oil (dipstick looks OK)
    2) Get a combustion gas tester from Harbor Freight - I assume these will work fine in the SS expansion tank? https://www.harborfreight.com/combus...tor-64814.html

    After that, if the head gasket checks out OK, I must have some other issue like maybe a defective thermostat. Not too hard to swap out so I could order another thermostat and see if that helps.

    If that still doesn't work, it's back to the drawing board.
    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

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