I recently bought a 91 runner. It was running a little cool most of the time which has an effect on overdrive shifting and performance. I bought a new thermostat and when I went to install it found that a previous owner has removed the thermostat all together. No wonder it was running cold ! I finish the job and didn't get 4 miles from home before I am overheated.
80 degree day, no A/C, 60 MPH. So here is what I have checked since then;
-No mud or debris blocking air flow.
-Fan clutch ok and pulling air the proper direction
-Water Pump is circulating coolant.
-Thermostat checks out OK on stove with a thermometer.
-Inside of radiator looks clean and coolant in good shape.
-No coolant in oil.
A couple more observations and then I need some help!!
Found a small amout of what appears to be pieces of black RTV circulating in the coolant. Any ideas ?
With no thermostat shouldn't it be running very cold instead of close to normal ?
Also what are the protocols that operate the electric fan ? I can only get it to come on when the A/C is turned on.
This is the V6 model.
I am:

 

Maybe its a dumb question, but do you have the right thermostat?
I once had one (aftermarket stuff) that was too long and didn't open fully when mounted in its housing.

 

Ive had that problem before when changing thermostats. My conclusion is that you get air trapped behind the thermostat and then it wont open up so the vehicle gets hot. I usually just let it warm up then shut it off a time or too and itll eventually open up. Is your top hose getting hot? I think that will tell you if your thermostat is opening up (I think). Just my 2 cents

About the electric fan, I think from what others have posted it is only supposed to come on when the ac is on. The engine could be on fire and that fan wouldn't know any better

 

Make sure the thermostat is in the right way. I also had a problem with an aftermarket thermostat not working correctly. A Toyota thermostat is definitely higher quality. If it runs cool without a thermostat the thermostst is the problem of the overheating.

 

The thermo I put in is an aftermarket but it does open at 180 and has the same physicial shape as the one drawn in the service manual. I installed it per manual diagram with the jiggle valve up. Wouldnt that jiggle valve let enough coolant seep through to fill any air voids ? Thanks for the electric fan info.

 

This idea may sound a little odd but the RTV brought it to my attention. Wimpywade had a problem because of some gasketmaker. Here is the thread. His post about what happened is the 7th post down.

What did you do to check the water pump?

Try this. Run the vehicle until is gets hot and try to feel around on your radiator. If you feel any cool spots those are places where the lines are blocked and no coolant is flowing through there. If the whole thing is cool I would look at the water pump again.

Just my $.02



EDIT: I posted a link for another thread...oops .

 

Hey ag, Gig em' ! I got a kid down there now gettintg out next Dec.
I did a visual check of pump function by not completely filling the radiator and cranking up. Circulation appeared to be robust. I wasn't able to follow your link to wimpywade's post. Could you do it again. Thanks.

 

When I said backwards, I ment with the spring assembly facing the front plastic dome instead of into the block. I did this on accident with an aftermaket one. The stock thermostat can only be installed the right way. Another thing I had to do is pour coolant back down the upper hose after replacing my thermostst. It got an air bubble around the thermostat that would not come out without filling from the top tube. Mine overheated badly when it had the air bubble in it also.

 

I finally got a chance to work this issue again. This time I took the time to let it heat up and cool down several times (about 8) to see if any air voids would fill up. My results are very consistent :
-Approx. 3 minutes to reach normal operating temp.
-It would hold steady there for about 3 or 4 minutes and then start climbing again to the transition area between white and red.
-It would hold steady there for about 3 more minutes and then start climbing into the red. The only thing that would keep it from pegging is heater on high.(Which has burned in my fan switch so it is stuck on high!)
If I just let it sit and idle the temp would hold steady at normal.
Due to daily driving needs I removed the thermo (for the umphteenth time) and started trying to block off part of the radiator with cardboard to see if I can make the temp go up. The first piece about 10 x 12 made no difference. I am going to try a larger piece and see what it does. If nothing happens then I know that I have a circulation problem somewhere. Radiator blockage or pump. Right ???

 

Mine is controlled by a thermocoupler jammed into the radiator fins. I do not have the AC control hooked up. Works fine this way.

 

I think Mark is talking about the AC fan, not the engine cooling fan. In his first post Mark said he checked the clutch fan so he still has the original fan.

Cruizin has the two mixed up because, yes, the AC fan only comes on when the AC is turned on. But, aftermarket electrical engine fans have the fan controller that uses the probe that gets jammed into the radiator fins.

 

Ooops! Forgot about the ol' AC fan. :pat:

 

I dont think I have an answer for you, but something that happened to me is when I had head work done, the shop put the head gaskits on BACKWARDS. Yes, it can be done. This caused an overheat situation something like yours. The shop that did the work thought it was an air pocket and took it to a place that had purged others. The end result was the other shop cut the middle of the thermostat out. This allowed it to run at proper temp during the summer (when I got it back) untill the fall. Then it acted like yours and would not fully warm up. When I found the cut t-stat, I was livid. My mechanic swore he had nothing to do with it and would fix it up for me. End result was that the head gaskits were on wrong and plugging up a coolant passage. They replaced the gaskits properly and got it all setup at no cost to me. So, has it had headwork done to it before you got it?

Also, the RTV in the radiator seems to get there whan the front cover has to be taken off I guess. I found a couple in ours also.

 

Is the rad cap the right one and is it holding pressure? Someone before you may have installed the wrong one or it could be worn out. I too have found black rtv floating around and I can't find the source. Could be you have a blockage somewhere of built up rtv? let me know if you find the source.

 

Wow, that is really interesting.
I know of a few who had complained of overheating problems and had put multiple thermostats in the vehicle only to have it do the same thing again. I won't let anyone touch my truck because it is such a headache to track down a problem like that.

 

Well this is all very interesting. When I sent in an email asking Toyota if there were any outstanding Service Campaigns on this VIN their reply included;

SSC#: V06
SSC Name: V6 Engine Headgasket
Dealership: Millennium Toyota
Date: April 10, 2000

Could a Dealership have installed these wrong ?
If this is the problem, what do I do ?
a. Replace head gaskets again on my own.
b. Twist Toyota's arm to redo it ?
c. Live with it ?
I cannot be certian what happend to this vehicle between April of 2000 and the time I purchased it this September.

Right now I have the radiator partially blocked so that the engine will get up to temp. It takes longer to reach operating temp but seems to hold ok after that

 

The toyota dealership here in my town were the first ones that told me that they could be on backwards. The service manager admitted that he had seen that happen there in their shop once or twice. If you dont pay attention, its easy to screw it up. So if my local dealership admitted to doing it, im sure others might also.

What to do......
IF it is in fact the gaskets, the place that put them on backwards IS liable. Now, theres no way I know of to find out if they are backwards for sure, except to pull the heads.

I assume that what you found out means that the gaskets were replaced in april 2000. Thats how I read it. I could be wrong though. You cant track the previous owner? Did you buy from a dealer, or an individual? Keep us posted.

 

I know this sounds crazy but I bought my Runner off of Ebay from a dealer. Flew into New Jersey and drove it home to Texas. The title only listed the dealers name. Carfax showed only two previous owners and I have no idea how to get info on them. The truth is I have no idea what the truck went through from April 2000 till I bought it in Sept. 03. Other than this perplexing issue it has been a primo truck. I'm not sure what to do now. With the radiator partially blocked it gets up to operating temp in about 7 minutes and holds a good temp.(Meaning guage shows a good temp and the O/D shifts correctly) I guess I am somewhat satisfied with this and may not pursue it any further unless I am removing the intake for other reasons.

 

I would call the Toyota 800 number and bring the issue up with them. They were the ones that paid Millennium Toyota to perform work and it is apparent that something is not right about the vehicle and thus the work is potentially suspect. The problem existed before you bought the truck......this is obvious because someone removed the thermostat so it would run well enough for them to drive it and also for you to buy it. I would put it into Toyota's hands and see what they say. I presume that Millennium is probably not near you or I'd say to start there. How good of a relationship do you have with your local Toyota dealership? They would be glad to get Toyota to fund the work again.

David