[Mellow77]

I would like you to take a journey with me and offer your opinions as to what you think could be the problem based on symptoms observed. Think of it as a word problem on crack. Please read, vote and offer your comments. I will then post what I've since found out.

Observation - noticed the rig would begin getting hot sitting in the TX heat, AC on blast while in stop and go traffic or while parked someplace. On a couple of occasions I shut her off to cool down as it was apparent overheating would occur in short order unless I did so. I also noticed that turning off the AC made a considerable difference in whether or not the rig would start to overheat.

In preparation for an elk hunting trip to CO I made a few changes in an attempt to cross off the overheating worry from the trip list.

New Parts: KoyoRad, DexCool fluid, 170 degree thermostat, temp probe / fan relay / temp adjustable harness and SPAL electric fan in place of the factory fan and shroud. I also installed a Satoshi modified grill I had been working on at the same time.

Trip happenings:
Drove from TX to KS (to pickup my Dad), then drove from KS to Denver with no problems. Pulling into the REI parking garage I could hear a very slight pinhole in the radiator. Observed occasional drips in the middle the radiator underneath the electric fan. Found a nearby shop to replace the radiator that evening before closing (on Friday). Once the newly old KoyoRad was out it became apparent the fan mounting pads failed and the center hub of the fan rubbed a hole in the cooling fins thus causing the leak. This is where things got interesting...

New replacement rad in, new green coolant (that he swears was Toyota compatible), and supposedly some new tranny coolant (he also swears is compatible with the brand new Dexron VI I just had put in during a full tranny service 3 days before). He admitted letting 2-3 quarts run out because he didn't cap the hoses while replacing the rad. As he's buttoning everything up, I was in the office paying for the service performed. Once done I walk around the corner and observe him hooking up the electric fan relay and I see him arc the ground and notice the truck was running.

Nothing seems to be hurt as a result, fuses look good, shop closes and I roll out finally headed to the mountains.

I notice the truck getting hot as I'm leaving Denver and starting to make the first long pull up the mountain towards the pass. The truck is fine on flat ground, slight hills or going downhill but gets hot when pulling up a medium to steep grade. I pull over and it becomes apparent the electric fan is not coming on despite hot coolant temps. I had extra relay fuses with me but replacing the blown fuse did not cause the fan to work. Some shade tree mechanic analysis at the crappiest Conoco station I've ever encountered confirmed the fan itself was fine and still functional but the relay and adjustable fan harness were both fried.

I wired the fan directly, bypassing the relay, so that I could get the truck to someplace for additional parts. With my MacGyver skills exercised the fan was back in working order but required stopping every hour or so to shut the fan off and give it a break since electric fans are not made to run continuously. Babied the truck and got out to Glenwood Springs for a white water rafting trip on Saturday since it was already scheduled and non-refundable.

Head back into Denver (Sat evening) for the best chance at parts and/or a shop to help figure out what's up. I finally located a new harness and relay, after trying 6 different parts stores along the way, and rewired the whole fan (in the parking lot) to ensure no lingering problems could exist. Fan was back in normal working order.

Took off again for the mountains and experienced the exact same overheating problem while trying to pull the long climb over the pass.

Back to the O'Reilly's parking lot for additional troubleshooting. Walked through each component to sort out what could be causing the truck to overheat. Ran the truck w/o a thermostat, flushed and replaced rad fluid, burped burped and burped again...etc. Nothing seems to be helping. The truck runs nice and cool sitting in a hot parking lot with the AC on blast but it overheats under load when pulling a steep grade.

No dice on getting her fixed so I finally checked the rig into a Toyota Specialist on Tuesday.

Play the part of the specialist and vote/comment on what you think could be causing the problem.

[JohnsD90]

Thats easy, shut the AC off in the blistering heat in stop and go traffic.

Change the fan clutch, and change the radiator and go from there. This does not sound like the head gasket. Water pump and Theromstat wouldnt hurt either.

[agloukhoff]

May sound silly, but try idling it on a steep incline and see if your temp rises.

[mmml4]

My brother had a Jeep many years ago act in a similar fashion. His water pump had the wrong impeller pressed onto the shaft. The water pump was replaced and problem solved.

[Mellow77]

Originally Posted by JohnsD90

Thats easy, shut the AC off in the blistering heat in stop and go traffic.

Done enough of that business already....it's f'n hot down here.

Originally Posted by agloukhoff

May sound silly, but try idling it on a steep incline and see if your temp rises.

I guess I inadvertently did that while trying to ensure all the air was out by burping the old girl. Temp held steady even after 20+ mins of idling with the air on "COLD".

[JohnsD90]

It does sound like your truck overheats only in extreme situations, when its under load up a hill hot out with the AC on, other than getting the stock fan to work properly ie install that new fan clutch, i am not so sure there is an actual problem with your truck. 100*F outside, witht he AC on will certainly push a motor, now going uphill for an extended period of time will definetley push the motor hotter. I would fix the and really just expect that if you push the motor to its limits like that, that it will overheat, i mean the air cooling that coolant is at lowest whatever the outside temp is, and then you have the extra heat from the AC in the engine bay so that engine bay is probably close to 150-200*F, i dont know how you can expect the coolant to be cool when the air its using to cool it is stagnent engine bay air mixed with a little outside at 100*F. I'm not sure you will find many 3rd gens that wouldnt overheat in that situation.

[agloukhoff]

Has there been any test for exhaust gases in the coolant? Does the system appear over pressurized? (Puffy hoses, whistling rad cap, foam?)

My truck with shot HG/Heads will idle all day long at 190, once you start driving though, it's a matter of time till it will overpressurize, blow a hose/gasket/cap and overheat.

Also get an UltraGauge so you can get some actual numbers. The dash gauge is useless. It doesn't really start to move from the middle for me till AFTER 230F which is already well into way too hot to be working right.

[kball]

You replaced the radiator but what about the cap?

[Grenvilleter]

Originally Posted by kball

You replaced the radiator but what about the cap?

Good point ! Also...make sure you set the climate control to hot and make sure you fill up the heater core.

Being new to Runners, I'm not familiar with how it's plumbed but perhaps there is an airlock happening there that is preventing maximum circulation but adequate under normal workload.
Any other vehicles I've had/worked on were susceptible to heater core lock-up after loss of coolant.

Failing that, I'd hate to think water pump but obviously there is inadequate flow when the engine is under load.

Check all the cheap stuff first including "rad cap" but is it possible the new rad is faulty ?

That said, I voted " I DON"T KNOW"

[steezemcqueen]

Originally Posted by JohnsD90

It does sound like your truck overheats only in extreme situations, when its under load up a hill hot out with the AC on, other than getting the stock fan to work properly ie install that new fan clutch,

electric fan. ie no fan clutch.

I don't think it is your fan because i would bet that the truck moving at 50-60 mph is gonna move much more air through the radiator than the fan will with the truck stationary. If the original red coolant wasn't COMPLETELY flushed out, that could be the cause since mixing the green with red can cause gelling. I know you say you flushed and refilled again but what does your coolant look like? If it kinda brown, i would

[NOT ME OR SOMEBODY]

Bad thermostat, but stuck open and or too low of a temperature
Rating. Get a 190 degree one.

Reason ..... When stuck open the
Coolant does not stay in the radiator long enough to be cooled.

[agloukhoff]

Originally Posted by NOT ME OR SOMEBODY

Bad thermostat, but stuck open and or too low of a temperature
Rating. Get a 190 degree one.

Reason ..... When stuck open the
Coolant does not stay in the radiator long enough to be cooled.

No. That's not the purpose of a thermostat at all. The reason you have on is to keep the engine at optimal temp which is between 170-200. If you run with no thermostat in cold weather you may never reach 160+.

Running without a thermostat at all will not cause any issues in warm weather but you will probably still run too cold which results in poor fuel econemy etc

Your theory about poor cooling due to high flow rate is flat out insane. The higher the flow rate the greater the cooling capacity up until it maxes out the heat dissipation of the radiator at which point you get a bigger rad. Some track cars run with no thermostats at all (one less thing to fail).

[NOT ME OR SOMEBODY]

Originally Posted by agloukhoff

No. That's not the purpose of a thermostat at all. The reason you have on is to keep the engine at optimal temp which is between 170-200. If you run with no thermostat in cold weather you may never reach 160+.

Running without a thermostat at all will not cause any issues in warm weather but you will probably still run too cold which results in poor fuel econemy etc

Your theory about poor cooling due to high flow rate is flat out insane. The higher the flow rate the greater the cooling capacity up until it maxes out the heat dissipation of the radiator at which point you get a bigger rad. Some track cars run with no thermostats at all (one less thing to fail).

Geez dude. wow

will you feel dumb when that is the solution?

optimal temp for a 3rd gen is 190. ( the OP has a 170 )

a track car is not a 4runner

It's not cold weather it's hot

Bigger rad thing is also not the case here ... not even going there you obviously wouldn't understand.

ps your kid needs a haircut.

[Grenvilleter]

Originally Posted by NOT ME OR SOMEBODY

Geez dude. wow

will you feel dumb when that is the solution?

optimal temp for a 3rd gen is 190. ( the OP has a 170 )

a track car is not a 4runner

It's not cold weather it's hot

Bigger rad thing is also not the case here ... not even going there you obviously wouldn't understand.

ps your kid needs a haircut.

You should take a welding course then start up your own garage !

[agloukhoff]

Originally Posted by NOT ME OR SOMEBODY

Geez dude. wow

will you feel dumb when that is the solution?

optimal temp for a 3rd gen is 190. ( the OP has a 170 )

a track car is not a 4runner

It's not cold weather it's hot

Bigger rad thing is also not the case here ... not even going there you obviously wouldn't understand.

ps your kid needs a haircut.

A 170 thermostat will not result in 170 engine temp. Even my "kid" who is dumb as a brick can figure that out.

I am not saying he needs a bigger rad or that it's cold - those were examples that I hoped would help you understand how cooling systems operate to maintain optimal engine temperature and how the thermostat plays a role. Clearly though my efforts were lost on you as you'd rather insult me than consider what I have to say.

Fact is that a stuck open thermostat cannot physically result in overheating without other issues with the cooling system. Seriously, the worst thing a stuck open thermostat will do is keep your engine temp lower than optimal – never ever higher. It’s physically impossible.

Not saying his thermostat ISN'T the issue - it may be stuck closed, opening late or not fully opening - it's certainly NOT stuck open.