Overheating Uphill...

[lossgenius]

I have a 2000 4Runner Limited and just recently this behavior started. Going uphill the temp rises, I never let it overheat, I would pull over and let it cool off. It is fine driving on local/hwy roads.

Radiator is about a year old, thermostat was changed at about 170k (currently at 203K). I have a trans cooler to prevent the dreaded pink milkshake. There is no leaks, oil looks fine, fan clutch seems fine, no smoking and no loss of coolant (toyota red).

The thing that I find odd is when I turn it off to let it cool down, when I start it up I get the CEL. The code says the TPS is failing.

My question is, can the TPS cause overheating going uphill? I searched the forums and could not find anything regarding the TPS and overheating.

I may try changing the thermostat but wanted to ask for advice prior..

Thank you in advance.

 

[alumarine]

What does the temp rise to?

 

[lossgenius]

I didn't wait to see how high it would rise but it was about a half cm below red.

 

[heat]

I'd get a second opinion on coolant temp- Torque Pro, add-on meter/sender,
IR temp reader, something.

 

[lossgenius]

Second opinion from odb scanner read 248 for the coolant.

Sent from my Pixel 2 XL using Tapatalk

 

[pluton]

Conventional wisdom:
If overheating while driving(not stopped): Poor flow. Causes: Clogged radiator, clogged somewhere else(less likely), underperforming water pump.
Clogged rad can be caused by mixing 2 incompatible coolants, like orange DexCool and any normal coolant. Happened to me once.
T-stat--- maybe. Replace T-stat with actual Toyota unit.

 

[jgue467]

I have a 2000 4Runner Limited and just recently this behavior started. Going uphill the temp rises,... thermostat was changed at about 170k (currently at 203K). I have a trans cooler...

It should not get to 248 going uphill or under Any condition for that matter. How much of a hill are we talking about, yet it doesn't really matter, I've climbed many mountains, all at under 200 for both engine and tranny.

So are you by-passed? If so, I highly recommend Against that, trans cooling system was designed to run through engine radiator, extra cooling is fine but not 'Minus' cooling.

T-stat: was it installed with jiggle valve down to 6? They can stick partly Open (or closed depending on how you think of it!), causing over heating or over cooling.

Have you removed the forward skidpan and looked Up between the A/C condensor and radiator? When I off-road where tall grass exists, it manages to clog up the space between the two. Use some kind of thin, long tool to get it out.

Luck. :cowboy:

 

[phattyduck]

If you see the needle move from the center position, you are already well on your way to overheating (I've seen engine temps up to 210*F and the needle never moved). With a good running cooling system, it should be nearly rock solid around 187-193*F.

Make sure the thermostat is OEM and the jiggle valve is at 6 o'clock (upside down from the way they are normally installed). There may be other cooling system problems, since overheating is otherwise very rare (air blockage, weak fan clutch, bad water pump, etc.).

-Charlie

 

[gamefreakgc]

248 means your coolant isn't flowing, that's way too hot for a stock engine to ever get.

Are there any clues, such as after getting up to temp the top hose is hot but lower is cold?

I suspect either stuck thermostat or failed water pump. Try running it without a thermostat and see if that fixes it. Was a common issue for older 4Runners.

 

[nevada]

I have a 2000 4Runner Limited and just recently this behavior started. Going uphill the temp rises, I never let it overheat, I would pull over and let it cool off. It is fine driving on local/hwy roads.

Radiator is about a year old, thermostat was changed at about 170k (currently at 203K). I have a trans cooler to prevent the dreaded pink milkshake. There is no leaks, oil looks fine, fan clutch seems fine, no smoking and no loss of coolant (toyota red).

The thing that I find odd is when I turn it off to let it cool down, when I start it up I get the CEL. The code says the TPS is failing.

My question is, can the TPS cause overheating going uphill? I searched the forums and could not find anything regarding the TPS and overheating.

I may try changing the thermostat but wanted to ask for advice prior..

Thank you in advance.

I suggest another look at the fan clutch.

 

[nissanh]

How old is the radiator? If it is more than 10 years, replace it. I had the same issue going uphill in Sierra's and found out the radiator core was clogged with sediments.

If you plan to replace the fan clutch, stay with AISIN or OEM, else expect to hear loud wind noise at all times.

 

[DaMonkey]

My question is, can the TPS cause overheating going uphill? I searched the forums and could not find anything regarding the TPS and overheating.

I would say so. The only thing TPS does is meter 'tip-in' for extra fuel when you press on the gas. Basically same job as an accelerator pump on an old carb. But TPS can go in reverse too when you lift. That's all it does, MAF takes care of the rest of basic fuel curve.

So TPS adjusts fuel mixture to be more rich or lean based on what your foot is doing.

Overheating under load... the cooling system is the obvious culprit, and gotcha number one is usually ignition timing, but fuel mixture can absolutely overheat your motor under load.

If your TPS is intermittent it could overheat your motor. Take a look at your plugs should show you if you are running rich or lean.

Just a guess. Others here may be able to comment if overheating from rich or lean might throw other codes too like the o2 sensor stuff. But maybe it does not throw a code because it's expecting it to be rich or lean based on what the TPS is telling it.

Good luck.

 

[rickmum]

Damn.

I had my AT TEMP light go off once. 1998 Automatic transmission with tranny cooler bypass in 2nd gear, 4HI and OD was on - going up a very steep gravel road. I was driving like for for maybe 4-5mins straight crawling, and the light went off.

Thankfully I was at the top of the hill right when I got the light so I shut the engine off, popped the hood and let it cool off for 10 mins.

The coolant and transmission fluid was fresh 2 months prior.

I think I'm going to put a new radiator in and use the radiator + cooler and also add a transmission temperature gauge.

 

[lossgenius]

First off I would like to say thank you to all of you that shared your knowledge/suggestions... The culprit was the thermostat.. Thanks again for everything....

I'd get a second opinion on coolant temp- Torque Pro, add-on meter/sender,
IR temp reader, something.

I will look into purchasing one of these.

Conventional wisdom:
If overheating while driving(not stopped): Poor flow. Causes: Clogged radiator, clogged somewhere else(less likely), underperforming water pump.
Clogged rad can be caused by mixing 2 incompatible coolants, like orange DexCool and any normal coolant. Happened to me once.
T-stat--- maybe. Replace T-stat with actual Toyota unit.

T-stat was the culprit.. it was a OEM installed by the dealership.. I purchased a new OEM one and installed it..

So are you by-passed? If so, I highly recommend Against that, trans cooling system was designed to run through engine radiator, extra cooling is fine but not 'Minus' cooling.

I am bypassed, have been for over a year.. I will look into adding the radiator back into the flow.

T-stat: was it installed with jiggle valve down to 6? They can stick partly Open (or closed depending on how you think of it!), causing over heating or over cooling.

This was the culprit.. the thermostat was stuck.. I replaced it and it seems to be back to normal. I ran it up the mountain that I noticed it on and the needle stood below half.. Temp didn't exceed 189

If you see the needle move from the center position, you are already well on your way to overheating (I've seen engine temps up to 210*F and the needle never moved). With a good running cooling system, it should be nearly rock solid around 187-193*F.

Make sure the thermostat is OEM and the jiggle valve is at 6 o'clock (upside down from the way they are normally installed). There may be other cooling system problems, since overheating is otherwise very rare (air blockage, weak fan clutch, bad water pump, etc.).

-Charlie

Thermostat was the culprit.. the jiggle was at 6 o'clock and it was a OEM.. Replaced with a new OEM and everything is back normal..

248 means your coolant isn't flowing, that's way too hot for a stock engine to ever get.

Are there any clues, such as after getting up to temp the top hose is hot but lower is cold?

I suspect either stuck thermostat or failed water pump. Try running it without a thermostat and see if that fixes it. Was a common issue for older 4Runners.

Top hose is hard to squeeze when it was that hot.. stuck thermostat was the culprit.. replaced and back to normal

I would say so. The only thing TPS does is meter 'tip-in' for extra fuel when you press on the gas. Basically same job as an accelerator pump on an old carb. But TPS can go in reverse too when you lift. That's all it does, MAF takes care of the rest of basic fuel curve.

So TPS adjusts fuel mixture to be more rich or lean based on what your foot is doing.

Overheating under load... the cooling system is the obvious culprit, and gotcha number one is usually ignition timing, but fuel mixture can absolutely overheat your motor under load.

If your TPS is intermittent it could overheat your motor. Take a look at your plugs should show you if you are running rich or lean.

Just a guess. Others here may be able to comment if overheating from rich or lean might throw other codes too like the o2 sensor stuff. But maybe it does not throw a code because it's expecting it to be rich or lean based on what the TPS is telling it.

Good luck.

I will look into this still as it did throw that code.. thanks

 

[WYLDRNR]

Overheating problem uphill

So I have a similar issue on my 2001 limited 4Runner with uphill overheating. Things I’ve done to it so far.. radiator is 1 year old exactly 7/2024. I changed the fan clutch Aisin on 11/2024 and just changed the T-stat 6/2025 and did put it at the 6 o'clock position thinking that would fix the issue.. I’ve only put original Toyota coolant from Toyota and burped the system yet it keeps overheating.. any idea of what it could be????

 

[alumarine]

So I have a similar issue on my 2001 limited 4Runner with uphill overheating. Things I’ve done to it so far.. radiator is 1 year old exactly 7/2024. I changed the fan clutch Aisin on 11/2024 and just changed the T-stat 6/2025 and did put it at the 6 o'clock position thinking that would fix the issue.. I’ve only put original Toyota coolant from Toyota and burped the system yet it keeps overheating.. any idea of what it could be????

When you say overheating do you mean the gauge is going into the red?
Have you used an OBDII scanner to get the temp?