Overheating/Related Issues?

[Rowdog]

Hey all, I recently began to run into overheating issues on my 95 FZJ. Everything starts fine and maintains normal temp until about 30 minutes into driving in which the car's idle starts to slowly climb and the temperature starts to go up. I've put a new thermostat in and did a coolant flush, which kept the temp lower until about 30 minutes in. The one thing I've noticed that I'm wondering if may be related is that my IAT seems significantly higher than air temperature and climbs slowly along with the rpms. Would love to heat any input on what next steps I should take.
I realize overheat threads are plentiful, but I did not see any mentioning the high IAT and RPMs.
Thank you.

 

[jonheld]

Hey all, I recently began to run into overheating issues on my 95 FZJ. Everything starts fine and maintains normal temp until about 30 minutes into driving in which the car's idle starts to slowly climb and the temperature starts to go up. I've put a new thermostat in and did a coolant flush, which kept the temp lower until about 30 minutes in. The one thing I've noticed that I'm wondering if may be related is that my IAT seems significantly higher than air temperature and climbs slowly along with the rpms. Would love to heat any input on what next steps I should take.
I realize overheat threads are plentiful, but I did not see any mentioning the high IAT and RPMs.
Thank you.

IAT temp will almost always be significantly higher than ambient because it is measured by the temp sensor in the AFM.
When you say idle speed increases, what does it increase to? Idle speed should be 650 RPM at normal operating temp without AC.

Idle speed is controlled by the ECU/ISC, but the ISC has a limited range and it is based on engine temperature as well as AC compressor operation.

 

[Rowdog]

IAT temp will almost always be significantly higher than ambient because it is measured by the temp sensor in the AFM.
When you say idle speed increases, what does it increase to? Idle speed should be 650 RPM at normal operating temp without AC.

Idle speed is controlled by the ECU/ISC, but the ISC has a limited range and it is based on engine temperature as well as AC compressor operation.

When the temps are high and it's doing it's runaway idle thing, in drive is closer to 1200 and in park it will peak above 2k. I've got at least some of the overheat problems figured out, but still when the car is nearing 200 degrees, the same idle problems seem to appear.

 

[jht3]

for your increasing idle, make sure its not the throttle cable binding up. either reach down w/ your right hand and pull the pedal towards your, or use your toe.

i had an idle that would jump up like that, seemingly only when the engine was hot, and it was the cable. replaced it with a new one and no more problems

since you mention IAT, i'm assuming you are reading that and the coolant temp via OBD2 diag tool? what coolant temp is it telling you? people on this forum seem to freak out when the temp hits 190*F but that is far from HOT. at 225 i'd be worried, but not at 195.

 

[jonheld]

When the temps are high and it's doing it's runaway idle thing, in drive is closer to 1200 and in park it will peak above 2k.

As @jht3 said, that's a binding throttle cable. Pulling with your toe might not work because it would just slack the cable. I'd be under the hood looking at the throttle plate. You should be able to push it back to the idle position to verify.

 

[Rowdog]

for your increasing idle, make sure its not the throttle cable binding up. either reach down w/ your right hand and pull the pedal towards your, or use your toe.

i had an idle that would jump up like that, seemingly only when the engine was hot, and it was the cable. replaced it with a new one and no more problems

since you mention IAT, i'm assuming you are reading that and the coolant temp via OBD2 diag tool? what coolant temp is it telling you? people on this forum seem to freak out when the temp hits 190*F but that is far from HOT. at 225 i'd be worried, but not at 195.

I have noticed that pulling up on the gas pedal does usually drop the rpms roughly 200, but it's still much higher when hotter. I lubricated the throttle cable as thoroughly as I could, and it still sticks and is able to be relieved with my foot. Is it likely I just need to swap the cable anyway?

I have an ultra gauge. Temps when it was really an issue before I replaced the coolant, therm, fan clutch, and belts in that order would often get to 220 or just under before I would turn on the heater to relieve some heat. Peaked up around 236 or so when I first discovered how bad it was.

Since replacing the aforementioned items I haven't seen above 213, and when I do, the idle problem rears it's head, then as temps return to normal (who knows why,) the idle problem seems to improve. I'm hoping post coolant flush I've got some air bubbles that just need to work their way out before I get stable temps again.

 

[Rowdog]

Hey all, I recently began to run into overheating issues on my 95 FZJ. Everything starts fine and maintains normal temp until about 30 minutes into driving in which the car's idle starts to slowly climb and the temperature starts to go up. I've put a new thermostat in and did a coolant flush, which kept the temp lower until about 30 minutes in. The one thing I've noticed that I'm wondering if may be related is that my IAT seems significantly higher than air temperature and climbs slowly along with the rpms. Would love to heat any input on what next steps I should take.
I realize overheat threads are plentiful, but I did not see any mentioning the high IAT and RPMs.
Thank you.

IAT temp will almost always be significantly higher than ambient because it is measured by the temp sensor in the AFM.
When you say idle speed increases, what does it increase to? Idle speed should be 650 RPM at normal operating temp without AC.

Idle speed is controlled by the ECU/ISC, but the ISC has a limited range and it is based on engine temperature as well as AC compressor operation.

Also thought it was mentionable the IAT reads between 130-170 when fully warm on a 85 degree day. Speed doesn't seem to change anything other than that it climbs to those temps faster when not moving. That seemed remarkably high at highway speeds to me.

 

[lumbee1]

I recently replaced my snorkel however I drove the truck several times without the snorkel in place. My IAT was 120 to 140 however with the snorkel it's 70 to 95 depending on ambient. With the higher IAT, my Cruiser was at 190 water temperature which is a bit high since I'm normally 182 to 186.

 

[jonheld]

I have noticed that pulling up on the gas pedal does usually drop the rpms roughly 200, but it's still much higher when hotter. I lubricated the throttle cable as thoroughly as I could, and it still sticks and is able to be relieved with my foot. Is it likely I just need to swap the cable anyway?

I have an ultra gauge. Temps when it was really an issue before I replaced the coolant, therm, fan clutch, and belts in that order would often get to 220 or just under before I would turn on the heater to relieve some heat. Peaked up around 236 or so when I first discovered how bad it was.

Since replacing the aforementioned items I haven't seen above 213, and when I do, the idle problem rears it's head, then as temps return to normal (who knows why,) the idle problem seems to improve. I'm hoping post coolant flush I've got some air bubbles that just need to work their way out before I get stable temps again.

Have a read through this post:

Running hot and out of ideas....

For what it’s worth…

forum.ih8mud.com

 

[jht3]

Also thought it was mentionable the IAT reads between 130-170 when fully warm on a 85 degree day

those do seem high. i also have an ultragauge, but never really paid attention to IAT. i do on my turbo BMW, but on a NA motor i never do. i will now!

I have noticed that pulling up on the gas pedal does usually drop the rpms roughly 200, but it's still much higher when hotter. I lubricated the throttle cable as thoroughly as I could, and it still sticks and is able to be relieved with my foot. Is it likely I just need to swap the cable anyway?

i tried lubing mine as well, but with all the cracks and visible corrosion on the exposed innards, i just replaced it with a new OEM. much better. the throttle body now closes reliably all the time.

Since replacing the aforementioned items I haven't seen above 213, and when I do, the idle problem rears it's head, then as temps return to normal (who knows why,) the idle problem seems to improve. I'm hoping post coolant flush I've got some air bubbles that just need to work their way out before I get stable temps again.

at 213, i'd be concerned too. mine likes to run between 185 and 195. on the hottest muggiest days with the A/C on, i'll see it climb to 205, but then the thermostat opens all the way and the temps drops back to 195. somewhere in the FSM are the specs for the thermostat, which i looked up at one point, and my truck seems to track.

 

[jonheld]

somewhere in the FSM are the specs for the thermostat, which i looked up at one point, and my truck seems to track.

180F-203F