Engine temperature running hotter than usual

[82DMC12]

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
8) 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.

68451

[82DMC12]

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.

68452

[Bitsyncmaster]

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.

[DMC-Ron]

Never overlook the obvious. Is the water pump belt tight?
Ron

[Jonathan]

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?

[dmc4087]

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)

[82DMC12]

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.

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[82DMC12]

Never overlook the obvious. Is the water pump belt tight?
RonNew belt! And yes it's correctly tightened. I had the water pump out during all that work and it looked good, no obvious issues.

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[82DMC12]

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.

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[82DMC12]

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/combustion-leak-detector-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.

[cdrusn]

I've always included a compression test of each cylinder. Not only should it show a difference (lower) compression in at least one but maybe two cylinders it will narrow your search.

[82DMC12]

I've always included a compression test of each cylinder. Not only should it show a difference (lower) compression in at least one but maybe two cylinders it will narrow your search.

Not a bad idea. I did a compression test last year just for the heck of it (I have a gauge) and all six cylinders were between 149 and 153 PSI so I have a good reference. I also rented a cooling system pump tester and I bought a combustion gas tester at Harbor freight so hopefully should have some answers and rule out a few things later today.

[82DMC12]

Well here is what I learned today.

1) Water pump belt is sufficiently tight
2) Bought a cooling system pressure tester pump and tested two caps - a new 15 PSI made in England cap from DMCMW, and a 16 PSI aftermarket cap from O'Reilly. Both tested OK.
3) Pumped up the cooling system to 15 PSI and it held pressure for 75 minutes without dropping at all. I have one tiny leak somewhere in the radiator, likely at an end cap joint because I can't see where the leak is unless I were to remove the shroud and possibly the fans. This is a repro radiator from DMCMW and is about 7 years old. I'll have to address this at a later day because radiators seem to be out of stock, however the tiny leak (a few drips after an hour) isn't enough to lose pressure.
4) Did combustion gas test in the SS overflow bottle. Waited until the thermostat opened, waited another 5 minutes, then used the tester. No sign of combustion gas in the test fluid. So, I think I can successfully rule out anything head gasket related.
5) Re-bled the radiator using the DPI radiator bleed kit. This time I pinched off the hose between the Tee and the metal pipe where the return flows to so that I was positive anything coming out of the bleeder was actually coming from the radiator and backed-up from the return pipe. Definitely well-bled now.
6) Went for a test drive with the same results. By the time I got home 15 to 20 minutes later, my temp was just below 220 with fans roaring (confirmed both are turning visually) and they are not taking the temp down, but the temp also isn't rising. It hasn't actually touched 220F during all this episode.
7) Once I got home with the car idling and temp nearly at 220F, I used an IR thermometer gun to check various spots between the thermostat and otterstat and confirmed the temp is around 197 to 215F at most.

It's been suggested that maybe my water pump is worn and not moving as much water as it should. I did have the water pump out of the car when I was in the valley this spring and of course inspected it and did not see anything inside or outside that looked worn but I guess it's hard to say. I do know that this problem suddenly started and hasn't been slowly creeping up like I would think progressive wear to the pump vanes would do.

It's my belief that the fans should be able to cool things down enough where they cycle on and off at idle (with A/C off). That's not happening. In fact when I first started the car in my garage and was bleeding, etc the temp was about 175F. It wasn't until I backed out and started driving that the temp started to climb, especially once I hit about 55 mph for a few minutes. Then the temp comes up to 215F and won't come back down even back at idle.

Any great ideas on what to check next?

[82DMC12]

I forgot to mention one thing. Not sure if this is relevant. But I had to have the radiator cap off of the expansion tank so that I could use the combustion gas tester. I started the car cold with the cap off and let the car idle until the thermostat clearly opened so that combustion gas, if there is any, is circulating back to the tank. I started the car with the tank half full. By the time the thermostat opened, within about 5 minutes, the level was coming up in the expansion tank until it actually started to overflow and spill out, so I quickly went and shut off the car, and it continued to overflow for a moment after I shut the car off.

I then drew about a quart out of the tank before restarting the car so I could use the tester without accidently sucking up coolant into it. The instructions for the tester say to warm the car up without the cap so that's what I did.

I get that the coolant will expand as it gets hot but is that normal? Should the expansion tank overflow like that with the cap off?

[DMC-Ron]

I forgot to mention one thing. Not sure if this is relevant. But I had to have the radiator cap off of the expansion tank so that I could use the combustion gas tester. I started the car cold with the cap off and let the car idle until the thermostat clearly opened so that combustion gas, if there is any, is circulating back to the tank. I started the car with the tank half full. By the time the thermostat opened, within about 5 minutes, the level was coming up in the expansion tank until it actually started to overflow and spill out, so I quickly went and shut off the car, and it continued to overflow for a moment after I shut the car off.

I then drew about a quart out of the tank before restarting the car so I could use the tester without accidently sucking up coolant into it. The instructions for the tester say to warm the car up without the cap so that's what I did.

I get that the coolant will expand as it gets hot but is that normal? Should the expansion tank overflow like that with the cap off?

That amount of change in the level of the reservoir tank you're reporting seems excessive. My reservoir level sits about an 1 1/4 inch down when cold and does not overflow when hot. Liquid coolant obviously expands with heat but overflowing a tank that's only half full when cold is a lot of expansion. I would have suggested that you need to bleed your water pump but you mentioned that you have Toby's auto-bleed so that should be automatic. The DPNW self bleeder kit usually has a valve that can disable the auto-bleed. Has that been inadvertently closed?

Ron

[82DMC12]

That amount of change in the level of the reservoir tank you're reporting seems excessive. My reservoir level sits about an 1 1/4 inch down when cold and does not overflow when hot. Liquid coolant obviously expands with heat but overflowing a tank that's only half full when cold is a lot of expansion. I would have suggested that you need to bleed your water pump but you mentioned that you have Toby's auto-bleed so that should be automatic. The DPNW self bleeder kit usually has a valve that can disable the auto-bleed. Has that been inadvertently closed?

RonI have an older version of the Toby kit that doesn't have a ball valve so it's always bleeding off a portion to the overflow tank.

Maybe I'll order a new thermostat and gasket as well as do another look at the bleeder kit. Maybe something has obstructed the bleed screw inside the thermostat housing. Might be smart to get the new kit with the ball valve anyway.

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[David T]

On a car that has a good, tight, leakproof system, once it is properly bled, you should not need an "auto bleeder kit". If you keep getting air you either have a leak or a bad head gasket and that should be fixed.

[Helirich]

That amount of change in the level of the reservoir tank you're reporting seems excessive. My reservoir level sits about an 1 1/4 inch down when cold and does not overflow when hot. Liquid coolant obviously expands with heat but overflowing a tank that's only half full when cold is a lot of expansion.

Ron

That is an interesting observation. I might have to try this test. This is the only car I have that has a reservoir tank, but every other car will overflow if the cap is removed and warmed up. Can’t say I’ve ever measured how much. If water is boiling some where, I don’t think it would stop.

As far as the OPs issue, I lean to the water pump not pumping good. Maybe a good flush?

[FLUX @88]

Possible cogged heater core or radiator? I also recommend purchasing a coolant vacuum filler. Yes you can fill and bleed the car normally but I have had great success using a vacuum filler to eliminate any air in the system.

[David T]

A vacuum filler makes filling faster and does not require as much bleeding but you will still have to do some bleeding of air. The major benefit to using a vacuum filler is that you can get all of the coolant in without having to wait for the thermostat to open by warming up the motor. Always check that the thermostat has a jiggle pin or at least a tiny (1/16") hole to allow air to pass. Another tip, the gasket fits AROUND the thermostat, the edge of the thermostat fits into the groove of the gasket.

[FLUX @88]

a major benefit of vacuum filling is eliminating most if not all trapped air :)

[82DMC12]

Thanks everyone. I've been busy lately but had a bit of time to keep working on this overheating (?) problem last night. I have now installed a ball valve in the thermostat self-bleeder line so I can bleed it off but then stop it so I'm not constantly bypassing hot coolant to the reserve tank. Last night I double-checked the alternator/water pump belt and tightened it up just a bit more. I also idled the car and waited until the thermostat opened. Then I opened the ball valve long enough to get the bleeder hose good and hot (telling me coolant is running through and not air) before closing it again. I did this twice while the car idled for about half an hour. During this time the fans kicked on just past 160F mark, and they would run for about ten minutes before cycling off. The fans cycled on/off twice so at idle anyway I seem to be maintaining good cooling.

This weekend I should have time for a test drive so I'll see how that goes - maybe I still had air stuck near the thermostat?? Or maybe the continuous self-bleeding just wasn't getting the air out.

68490

[David T]

When you are driving (and not running the A/C) the fans won't always run because when the car is moving, air is moving through the radiator so the cooling system doesn't need the fans unless it is very hot. That is normal, just watch the temp gauge.

[82DMC12]

When you are driving (and not running the A/C) the fans won't always run because when the car is moving, air is moving through the radiator so the cooling system doesn't need the fans unless it is very hot. That is normal, just watch the temp gauge.

Right. My problem before was the temp kept rising up to nearly 220F and wasn't falling even if I was driving at 55 MPH. If I can drive it for 30 minutes and the temp stays closer to 160F like it always used to (and fans cycle on/off if standing still at idle long enough) I'm going to call it good! Previously, the car would idle , hit 160F and the fans would come on, but they never shut off because it seemed like they weren't cooling enough. I'm glad to see they were cycling now and the gauge was hovering just above 160F in the meantime.

[bytes311]

Purely anecdotal, but my fans kick on around the 160F mark and generally run for a couple of minutes. 10 minutes seems like a long time at idle to cycle off?

[David T]

There are some variables like ambient temperature and every "O" switch is a little bit different. As long as the temp doesn't get over 220 F (and even that is variable, the temperature gauges are not known for accuracy). Make sure the fans are not shutting off because the circuit breaker popped and resets.

[82DMC12]

Purely anecdotal, but my fans kick on around the 160F mark and generally run for a couple of minutes. 10 minutes seems like a long time at idle to cycle off?

I'll probably come back to this thread a bit later as I'm working on a couple other small issues right now, but seems like NOW my fans come on just above 160F and the temp kind of runs between 160F and 180F (a bit higher when A/C is on) but the fans aren't cooling it enough to cycle off again very often. I haven't had much time to test it but I drove it for about 30 minutes and let it idle in my garage for a while and the temp was just kind of stuck right about 165F and the fans didn't stop after 15 minutes.

At this point I don't seem to be close to overheating anymore so I need to work on a couple other issues before I return to this. Thanks everyone for the help so far and I'll check in again later.

[ssdelorean]

Well here is what I learned today.

<<snip>>

It wasn't until I backed out and started driving that the temp started to climb, especially once I hit about 55 mph for a few minutes. Then the temp comes up to 215F and won't come back down even back at idle.

Any great ideas on what to check next?


Possible cogged heater core or radiator? <<snip>>

I was thinking a possible radiator clog or at least a restrictive flow than what normally is suppose to happen. Your mention of not happening until driving the car is what got me to think that. I had a slightly similar issue where my temp would go up at highway speeds (AC on or off, didn't matter) but driving at slow 25mph or idle speeds would be fine. Ended up being a clogged radiator.

[Bitsyncmaster]

You want the fans to kick on above the thermostat opening temp. You would also want the fans to turn off a little below the turn on temp. If you have the fans go on to low then they will run all the time your hot engine is running. But with most of us running AC all the time the fans run all the time anyway.