lee

recently (as of the high temps) i have seen my temp guage rise significantly under certain circumstances.

here are the symptoms as i have observed them. i have been testing it out for the last 4 days and this is what i find:

the engine's temp guage only rises when the a/c is on in 90 degree + muggy weather. now this is a/c of any kind, including when the dial is set to the defroster. it will be fine at first then slowly rise. it does not really lower at highway speed, but rises quicker when in stop-and-go. it does lower when i put the heat on all the way (which is torture), and if i just turn the a/c off.

it usually takes about 15 mins into a normal drive (not necessarily stop and go, not highway) to start reacting in that 90 degree weather.

the guage does not rise AT ALL and stays PERFECTLY EVEN on days like today -- 70 degrees, light wind, etc in any environment (highway, stop and go, low or high blast, etc). i tested it when it was in the 80s yesterday and it was FINE

now, for reference:
-I changed out the thermostat
-I powerwashed the radiator, it looks good, no noticeable huge clumps
-I have not yet tested the radiator with an infrared thermometer... thats the next step.


any other clues or ideas here? this is horrendous when its 90s and humid out guys, i can barely drive my truck.

but it is PERFECT in the 70s and 80s.

thanks!

MTL_4runner

Hey Lee,

The temp guage should stay pretty near rock solid under all driving conditions (the thermostat is designed to keep the engine at optimum operating temp so you get the best efficiency you can). The fact that at a certain outside temp, even with assuming the thermostat is fully open, your cooling system is failing to cool the truck (I assume the truck is not running lean for any reason as well). I also assume the fan shroud is also in place and not damaged either.

My suggestion for things to look at:
1) Flush the engine (with thermostat removed) and change coolant if you haven't lately.
2) Inspect the fan clutch (if it spins freely is may not be providing proper cooling)
3) Check to eunsure you have good coolant flow with engine hot and running (squeeze coolant hoses and verify you feel coolant rush by and that both hoses are relatively hot). If not you may have a WP with a worn impeller.
4) Inspect the radiator for any blockages or sediment
5) Use a boiling pot of water to reverify the thermostat is opening properly

lee

thanks Jamie:

My suggestion for things to look at:
1) Flush the engine (with thermostat removed) and change coolant if you haven't lately.
coolant was changed about 2-3 months ago -- should i do it again now that i changed the thermostat?

2) Inspect the fan clutch (if it spins freely is may not be providing proper cooling)
2 ne4roc members and i tested it and we all agreed it looked good

3) Check to eunsure you have good coolant flow with engine hot and running (squeeze coolant hoses and verify you feel coolant rush by and that both hoses are relatively hot). If not you may have a WP with a worn impeller.
thanks, ill look at this next

4) Inspect the radiator for any blockages or sediment
i power washed it, but it is a lot of work to gain real access to it... i may just have to do this..

5) Use a boiling pot of water to reverify the thermostat is opening properly
explain this for me?

thanks again!

profuse007

how did you powerwashed the radiator? interior or exterior?

grimpy

Did you recently change out the t-stat? You may want to double check the T-Stat as others have mentioned using hot boiling water... When you toss it in the hot water, it should open up... Even new t-stats may be faulty... Also you may have air in your system...

hillbilly

I'd think if the T-stat was somewhat malfunctioning, the overheating would persist whether the A/C was on or off. Did you install the new T-stat with the jiggle value between 15º of 12 o'clock as Bob write-up recommends? Initially, my first thought was the fan clutch, but there's a chance the water pump may not be circulating as well as it used to either.

lee

through the fan. but i guess thats not all that precise it really doesnt look clogged up.

as i said, yes i JUST changed it a week and a half ago or so. I dont think the t-stat is the issue, but ill try the hot water test

yep, i installed the t-stat exactly as Toyota and Bob stated. it was a really easy install and everything worked great till it hit 94 here.

thanks everyone keep the suggestions or advice comin'

profuse007

dont know exactly how you washed it but the heat-sink fins suppose to be spaced out as default. if you powerwash it or pressure wash it, then all of the fins will close(bend) together. so having a fan pullin in no air is just as good as not havin a fan at all. this will give you an idea and not drw any conclusio from.

i did similar to ur but i caught the problem.

MudMonkey

I completely removed my radiator 2 weeks ago. Took the hose to it and removed about 5-10 pounds of dirt.

But, then again my S/N is MudMonkey...lol

lee

i didnt really follow... sorry.

i didnt powerwash on full blast, i just rinsed the radiator off... there really wasnt much to aim at, as there wasnt much gunk.

profuse007

in that case, my description doesnt fall into ur problem. so no worrie

montypower

Replace the fan clutch. Mine did the same thing.

Intrepid

When my taco did this same thing, it would go up with the AC or if I was just sitting in traffic. I hit the radiator with a hose at home, nothing, then a power washer at the car wash. It still did the same thing. I ended up hitting it with a steam cleaner, removed both the grill on the outside and the fan shroud from the inside (a lot of the radiator is blocked by that) and I was amazed by the amount of mud that came out. I probably stood these hosing it for at least and hour and it kept coming, and it didn't look blocked to me before. You just have to keep the power washer/steam cleaner a good distance away so that you don't bend over the fins.

MTL_4runner

Thermostat testing:
http://www.deserted1.com/FSM/Repair_.../ther/insp.pdf

For the fan clutch make sure there is no silicon oil leaking out of the fluid coupling. You may want to get a spare from a junkyard to try if you can find one handy (if that's not it, you can easily unload it on eBay).

It doesn't sound like a dirty radiator is an issue either.

If you have an IR thermometer, then I'd definately take some temps while running to see if the radiator temp gradient is large (ie take some temps near the top left corner of the inlet hose then a few temps down near the bottom right corner and compare).

lee

if i used a non toyota radiator hose when i changed it recently, would that be a factor? if so ill go change to a toy one ASAP.

also: why would a brand new toyota thermostat be the issue?

boogyman

that shouldn't be a problem as long as the aftermarket hose is the same diameter as the toy hose.

rimpainter.com

Lee -

How "high" does the guage go? Are we talking middle, 3/4, in-the-red, or what?

Knowing all the things you have done thus far, I would take a close look at the mechanical fan like Jamie alluded to. Does it spin by hand when the engine is shut off (and it's hot)? It shouldn't.

Does the fan roar at start up or when you first take off on a hot day? It should.

I also assume the coolant level is good, correct?

984RNR

i recently cured my 2 year intermitent overheating problem by installing a new radiator.
It would only overheat on real hot days or sitting in traffic. The traffic was due to a faulty fan clutch that i relplaced w/ an electric and the controller bamachem recomends. It still persisted to over heat @ highway speed. I assumed the radiator was blocked. Installed the new one and it has been cool sailing ever since. If you can swing it lay under the car and attempt to feel the radiator after it has been running it should feel to be a uniform temperature. Any place that is blocked will be much colder. 90% of the parts of the rad i could feel were ambient temp while the motor was hot.

sorry about the babbleing

lee

How "high" does the guage go? Are we talking middle, 3/4, in-the-red, or what?
as high as ill let it go it seems. i wont let it overheat, so once it gets a smidge below the red (which is also a bit above 3/4) i turn the AC off.

Knowing all the things you have done thus far, I would take a close look at the mechanical fan like Jamie alluded to. Does it spin by hand when the engine is shut off (and it's hot)? It shouldn't.
it does spin by hand. i was told it should, but it should give some resistance, which it does

Does the fan roar at start up or when you first take off on a hot day? It should.
yes it does

I also assume the coolant level is good, correct?
correct.. did a full flush and change about a month ago

lee

thats not babbling! thanks. i guess ill try it out. ill use an infrared thermo first.