1996 Tacoma 2.7L overheats only when going up mountain pass

Hi,

Recently started having an issue where my 1996 Tacoma 2.7L with 211k miles overheats when I drive up mountain passes. When I drive on the highways in Denver it runs completely fine. I recently took it to an auto mechanic in town and they were unable to figure out what was wrong with it. The mechanic did say it could be early head gasket problems. Although, they couldn't find any proof of headgasket problems (doesn't leak coolant, doesn't have exhaust fumes in coolant). They also couldn't get it to overheat, because they drove it around town, and not mountain passes.

Recent things I changed

-Radiator cap
-thermostat

I have owned this truck for 6 years and only had one issue with the coolant system.

When I first purchased it, I thought the head gasket was bad, so I put the head gasket sealer in. (terrible idea, semi clogged my heater core, and flushed it out a bunch of times to heat) When I took it to a mechanic, the water pump was bad.

Below is a video I took when driving up a pass outside of Denver.

https://www.youtube.com/watch?v=KhMeIUJ5H74

 

I have found the gauge to not be a very reliable indicator of what is actually occurring. While I agree, the fact that is rises at all is concerning, it isn't really telling you much.

Going up a long grade will tax the system more, but the system should have enough headroom to easily handle the extra load. First thought is the radiator itself. They become inefficient with age and sometimes the lower half of the radiator's cooling fins can get plugged up with debris, making the system less efficient. Same goes for t-stats, they can become 'lazy', slow to react to changing conditions.

FWIW, You are solely relying in the idiot gauge. I believe your '96 is OBDII compliant which means there is a data stream that you can tap into for more accurate coolant temps (among other things).

 

There is no reason for concern. While the gauge doesn't indicate a temperature number, it doesn't rise much and not near the "red zone" or overheating.

At most, I' suggest to pull the radiator. Then have a radiator shop clean it out. This recommendation is only because you dumped a can of miracle cure into the system.

 

I would definitely hook up an OBDII reader so you can get an accurate reading of your temp. The dummy gauge on the dash isn't worth much except inducing panic when it decides to shoot up toward red.

Hook up to the OBDII port and see what your temp really is when climbing that grade. Around town you should see 188 - 190˚. The highest I've ever seen my temp climb when pulling up steep highway grades is 207˚, and that was carrying a lot of gear (plus supercharged, which introduces more heat).

Auto or manual trans? The auto trans trucks seem to run higher temp-wise going up long grades without trans coolers.

But until we know what temp you're actually getting it's all speculation. You mentioned putting that HG stop leak stuff in years ago, I wonder if it's coming back to haunt you again. Always avoid that stuff

 

Thanks for the replies. A few additional comments. This never used to heat up like this going up these passes. I also feel like it has been getting worse. My plan was to change the radiator, and possibly the water pump while I was close. To see if that makes a difference.

 

You've done the obvious stuff. Water pump is unlikely since it's just a spinning metal blade off of the drive belt. I'm assuming you don't have an air bubble either. If turning on your cab heater full blast helps cool it a little, I would point to the radiator not having the capacity it used to. You might have some corrosion and clogs in it. At the age of your truck I would at least try a reverse flush the radiator. Good luck.

 

It is a manual transmission. I will go pick up a ODBII reader to get an accurate temp.
That is also my concern. I have flushed the cooling system a couple of times since then, but I wonder if a bunch of it didn't come out.

 

1) Auto or manual transmission ?? , a slipping clutch orthe clutch pack/ bands in an automatic transmission are bad causing the transmission to slip which makes the engine work harder . Also if you've got an automatic and the trans temp getting close 250° or hotter . This extremely hot transmission fluid when passing thru the radiator trans cooler will superheat the engines coolant

2) clutch fan worn out not allowing air to be pulled thru the radiator


3) radiator cooling fins clogged with debris

 

I once had a similar overheating problem with my 2.4 96. It turned out to be a clogged radiator. If it's the original radiator, try a new one. Not sure if cleaning out the old one is effective enough.

 

It's a manual tranny, the shop did say the clutch has a slip, but it isn't causing power issues

 

Thanks, that is what I am going to try.

 

What color coolant are you using/ have you been using to flush?

Not exactly the same but close enough: I've run into electrolysis issues on older 22R toyota motors where they're using green coolant and it'll eat away at the water pump fins making em smaller and reducing their efficiency. If you don't know when the water pump was changed last and suspect it of being original I would absolutely change it.

Also you can test your thermostat by dropping it in a pot of boiling water and making sure it's actually opening up the way its supposed to

 

I changed the water pump 5 years ago, with one direct from Toyota.

Also, I believe the red coolant is in there now, and for the majority of the time I have owned it.

 

That's good, nevermind the second part then. Just for sanity sake I would still do the thermostat in boiling water test

 

Hi All,

I changed the radiator this evening and drove it up Floyd hill (a long pass). Didn't have any overheating issues, or temp increases. Thank for all the recommendations

 

if you havnt tossed the radiator already, pry the tabs that hold the top tank off and take a look. I am curious if the tubes are partially pluged. If so, upload a pic.

 

Here you all go. It's pretty nasty

 

I bet my heater core looks very similar

 

thank you.

 

Wow, seeing is believing. Glad you found the cause and were able to fix it so easily. It would have been interesting to have accurate before and after temp data, but alas, that would be purely academic at this stage. Once again, glad you're up and running.