Running Hot

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I am experiencing an issue where my coolant temps creep towards the red line if I am idling in gear on a hot day with AC on, usually in direct sunlight. Usually this only happens after I have been driving for at least 30 minutes. When this happens, I usually put the vehicle in park, and rev the engine to ~2k rpm to blow the fan clutch until it cools down. I have gone in the engine bay and measured temps via laser gun, and it seems to agree with my temp gauge. I have performed a HG test- I removed a couple inches of coolant, drove the car until it got hot, let the gauge creep up, then tested. No color change. I am not experiencing loss of coolant either.

The following were replaced in 2020, all brand new OE Toyota where not specified:
  • Thermostat & gasket
  • All coolant hoses
  • Aisin blue hub, valve set earlier, drained and filled with 45-60ml 15k oil
  • Temp gauge modified with resistor mod
  • EGR bypassed/blocked
  • rear heater delete
  • Radiator cap

The heating issue started happening towards the end of 2021, and now it is very prominant.
A few weeks ago I attempted to fix it by replacing/performing (to no effect):
  • Radiator (TYC brand) & cap, old was CSF brass unit
  • Coolant flush with 30 gallons of water and prestone flush
  • Aisin Water pump
  • Fan shroud (used OE, uncracked)

At this point I am suspecting my OE thermostat is not opening fully. Either that or something funky is going on with my fan clutch.
I can hear my fan clutch when I rev the engine but it does not sound as strong as my 60's fan clutch. Not sure if that's because the 80 is more insulated or not... I did notice when I removed the water pump that the inside was a matte charcoal color. Will try to take a picture and upload.

My question to the gurus: is there anything else I could be missing? At this point I'm curious if there's something else going on, like similar to how a car runs hot when the valve timing is retarded.

I feel like I also have a loss of power, but I'm not completely sure.
 

80t0ylc

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Did you seal the radiator/shroud with foam rubber or equivalent when TYC was installed? In extreme heat it is imperative and necessary to get good air flow through A/C and engine radiators.
 
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Did you seal the radiator/shroud with foam rubber or equivalent when TYC was installed? In extreme heat it is imperative and necessary to get good air flow through A/C and engine radiators.
No but the gap is very small, my shroud is not warped- I had done this in the past before swapping radiators but did not see an appreciable difference. Also tried water wetter with the previous radiator, no noticeable difference. I may try some aluminum tape.

This rubber foam was not there from the factory, I feel that there is some condition present in my vehicle causing it to act abnormally, but I can't think of anything.

Also: no issues overheating on highway or while moving, just while sitting still.
 

80t0ylc

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Seal is also needed between radiator and body/mount. I believe that's even more important given it's possibly a bigger gap. Another thing to check: Does the fan clutch ramp up to be fully engaged (most roar or loudest) to move the most air when idling hot?
 
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Seal is also needed between radiator and body/mount. I believe that's even more important given it's possibly a bigger gap. Another thing to check: Does the fan clutch ramp up to be fully engaged (most roar or loudest) to move the most air when idling hot?
I have never been able to hear my fan clutch engage while idling in gear @ 650rpm :oops:

But it is also this way on my fj60 and every other fan clutch vehicle I've owned. Should I be able to hear it audibly at hot idle?
Can anyone verify this?
 
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I just finished a headgasket R&R. The cooling system was flushed, drained and refilled. All hoses were replaced. Since the head was removed and cleaned, I know it's flowing well. I have not replaced the water pump, solely just because its not leaking.

My newly repaired '95 80 is also running hot (203°F), compared to my (other) '95 80, which runs steadily at 176°F. Neither of my fan clutches are working; I have the fluid R&R on my list for both. I just bought a Toyota thermostat (90916-03117) to fit into the headgasket replaced 80. Prior to installation, I tested it several times, for function setpoints. My very accurate analog (mercury) candy thermometer indicated that the opening point (initial valve movement) was after 180° (the FSM acceptable range is 176-183°F). It was fully open at 203°F, however, it took most of the end (higher) temp range to get the valve fully open.

I have not tested my (cold) thermostat (sorry, but that's not going to happen). I'm hoping the thermostat is the temp rise root cause. I do not, unfortunately, know whether an overheating condition led to the headgasket failure, since I wasn't driving when it happened, and don't regularly drive it. When I pull the current valve, I'll test it and post the result.

Based on your list, I'd lean that way. I'm not sure valve timing on the 1FZ-FE makes an operating temperature difference. IME, it runs when the timing's right and doesn't, or at least not well, when it's not.
 
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I just finished a headgasket R&R. The cooling system was flushed, drained and refilled. All hoses were replaced. Since the head was removed and cleaned, I know it's flowing well. I have not replaced the water pump, solely just because its not leaking.

My newly repaired '95 80 is also running hot (203°F), compared to my (other) '95 80, which runs steadily at 176°F. Neither of my fan clutches are working; I have the fluid R&R on my list for both. I just bought a Toyota thermostat (90916-03117) to fit into the headgasket replaced 80. Prior to installation, I tested it several times, for function setpoints. My very accurate analog (mercury) candy thermometer indicated that the opening point (initial valve movement) was after 180° (the FSM acceptable range is 176-183°F). It was fully open at 203°F, however, it took most of the end (higher) temp range to get the valve fully open.

I have not tested my (cold) thermostat (sorry, but that's not going to happen). I'm hoping the thermostat is the temp rise root cause. I do not, unfortunately, know whether an overheating condition led to the headgasket failure, since I wasn't driving when it happened, and don't regularly drive it. When I pull the current valve, I'll test it and post the result.

Based on your list, I'd lean that way. I'm not sure valve timing on the 1FZ-FE makes an operating temperature difference. IME, it runs when the timing's right and doesn't, or at least not well, when it's not.
Good anecdotal evidence- thanks. I am suspecting my toyota thermostat 90916-03117 is operating how you described yours. It certainly seems like there is some bias. When I first start the 80, there are no issues within the first 30-60 minutes. After a long highway drive and pulling into a drivethrough, however, it wants to go into the red.

I do not actually suspect valve timing, but was listing it as an example of things that can also induce overheating in engines, just in case there was something weird about the 1FZ that I did not know about.

Question is, should I try another Toyota thermostat, or maybe an Aisin THT-015? They appear to be different based on their photos.
 

80t0ylc

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I have never been able to hear my fan clutch engage while idling in gear @ 650rpm :oops:

But it is also this way on my fj60 and every other fan clutch vehicle I've owned. Should I be able to hear it audibly at hot idle?
Can anyone verify this?
You can step on the gas pedal to run the engine about 1200-1500 rpm and see if it sounds like the "start up roar". That should tell you if it is fully engaged. Other than that, I'm not sure how you could test it.
 
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No but the gap is very small, my shroud is not warped- I had done this in the past before swapping radiators but did not see an appreciable difference. Also tried water wetter with the previous radiator, no noticeable difference. I may try some aluminum tape.

This rubber foam was not there from the factory, I feel that there is some condition present in my vehicle causing it to act abnormally, but I can't think of anything.

Also: no issues overheating on highway or while moving, just while sitting still.
FWIW, I've seen many 80s running well within temp range without a fan shroud, radiator skid plate or foam gasket. While that's obviously mot the best condition, I don't think it's the difference between "normal", warm and hot. Maybe you would see it on a digital gauge as a couple of degrees, one way or the other...
 
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You can step on the gas pedal to run the engine about 1200-1500 rpm and see if it sounds like the "start up roar". That should tell you if it is fully engaged. Other than that, I'm not sure how you could test it.
Yes when I do that, I do hear the fan clutch. That is how I've been cooling my 80 in drive-throughs... needle creeps up, turn AC off and rev to 2k RPM, fan is audible. Hold it for a couple minutes until temp comes down. Pretty annoying, and my thought is that it's not normal behavior.

Granted, I'm sitting in 105+ ambient temps in direct sunlight with AC on, but that still should not overheat a healthy system. My entire cooling system other than the engine is new at this point.
 
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FWIW, I've seen many 80s running well within temp range without a fan shroud, radiator skid plate or foam gasket. While that's obviously mot the best condition, I don't think it's the difference between "normal", warm and hot. Maybe you would see it on a digital gauge as a couple of degrees, one way or the other...
agreed, lack of foam gasket should not create a overheating situation... I'm suspecting faulty OE thermostat.
 
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Good anecdotal evidence- thanks. I am suspecting my toyota thermostat 90916-03117 is operating how you described yours. It certainly seems like there is some bias. When I first start the 80, there are no issues within the first 30-60 minutes. After a long highway drive and pulling into a drivethrough, however, it wants to go into the red.

I do not actually suspect valve timing, but was listing it as an example of things that can also induce overheating in engines, just in case there was something weird about the 1FZ that I did not know about.

Question is, should I try another Toyota thermostat, or maybe an Aisin THT-015? They appear to be different based on their photos.
I'd pull and check the thermostat functionally. I doubt it has failed due to the construction, but it, or the galley, may have some trash in it. You won't know for sure until you do, and it is an FSM function check for this condition. I can't recommend other than OEM thermostats; I've never used one. I do know the OEM is significantly beefier than the aftermarkets I've seen.
 
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Well, you do live in the high temp lab...
 

80t0ylc

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Yes when I do that, I do hear the fan clutch. That is how I've been cooling my 80 in drive-throughs... needle creeps up, turn AC off and rev to 2k RPM, fan is audible. Hold it for a couple minutes until temp comes down. Pretty annoying, and my thought is that it's not normal behavior.

Granted, I'm sitting in 105+ ambient temps in direct sunlight with AC on, but that still should not overheat a healthy system. My entire cooling system other than the engine is new at this point.
OP's problem occurs when idling or at slow speeds. IMHO that is a fan/airflow problem. If it was thermostat, vehicle speed wouldn't matter as much. And yes, radiator seal is essential for extreme heat performance - ask the AZ crew.
 
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Purely for the sake of idle curiosity, what year is your 80? And is this the OE head and gasket? If not, when were they R&R'd?
 
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Another observation:

On occasion when I stop for gas and start back up, the temp gauge will be in the red... it quickly comes back down once the engine is running, but still. What gives? Usually when I shut the car off the temp gauge will be about in the middle or a little above. But then while it's off it goes all the way to red. I know cars heat soak when shut off but I'd think it should get that hot! Looking for anyone with anecdotal evidence after temp gauge faker mod to know if this happens to them
 
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Purely for the sake of idle curiosity, what year is your 80? And is this the OE head and gasket? If not, when were they R&R'd?
1993. Not sure if original HG or not. No coolant consumption and no exhaust gasses found in radiator... I pumped the fluid for a good 5 minutes, stayed blue the entire time.
 
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OP's problem occurs when idling or at slow speeds. IMHO that is a fan/airflow problem. If it was thermostat, vehicle speed wouldn't matter as much. And yes, radiator seal is essential for extreme heat performance - ask the AZ crew.
Granted, I don't drive in AZ, now, but I have and you are correct, that's a different world. Big D is trying to be them this week.

Also, my temp is steady after 2-3 minutes from cold, no matter the vehicle/engine speed or load.
 
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Granted, I don't drive in AZ, now, but I have and you are correct, that's a different world. Big D is trying to be them this week.

Also, my temp is steady after 2-3 minutes from cold, no matter the vehicle/engine speed or load.
Temp gauge modded or not? Factory has a faker circuit that translates temp fluctuations into dead middle reading.
 
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Another observation:

On occasion when I stop for gas and start back up, the temp gauge will be in the red... it quickly comes back down once the engine is running, but still. What gives? Usually when I shut the car off the temp gauge will be about in the middle or a little above. But then while it's off it goes all the way to red. I know cars heat soak when shut off but I'd think it should get that hot! Looking for anyone with anecdotal evidence after temp gauge faker mod to know if this happens to them
I was just about to ask if you had adjusted the temp gauge. According to conventional wisdom, the US OE gauge won't move until it's too late for you to react; i.e., it'll read in the middle of the range at 176° just as well as 210°.
 

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