Water pump or t-stat?
 

I was driving to work today and my 88 4runner V6 started to overheat. I turned the heat on and it came out cold. After about 30 sec the heater started working again and my car temp dropped to where it normally sits. I drove for an hour without problems. Driving home from work it did the same thing after about 15 min. any ideas?

try changeing the t-stat first then go from there

is the fan clutch working properly?

also is it full of coolant?

id say its low on coolant

Yes, I top up the coolant before every ride. I'm either losing coolant threw the overflow when it overheats or internally. I could have wrecked the hg the first time it overheated because i do periodically have white smoke. fan seems to be working fine. If i turn the heater on get no heat even though my truck is overheating, does that not mean that the coolant is not circulating. Thanks,
jon

Your system could be air-locked, preventing adequate coolant circulation. Refill the system and properly bleed all the air out to see if that helps any.

How does one properly bleed the system? Ive read bits and chunks about "burping" the cooling system but have no idea what that is or entails....

Ill have to do it in about a month when my top end rebuild is done.

It appears crazy at first, but warm up the truck, heater on full - about 10 minutes - radiator cap off. Parked on a hill or slant - nose forward so they say.
It starts to errupt like a volcano so you will loose some coolant - have the 50/50 mix ready to top off and a pan underneath to catch. Skid plate off too.
For some reason, I was still affraid to do this even after I read all the threads on it. It appears that it will not stop so the tendency to to quickly put the cap back on - don't. I then squeze the upper hose a few times and check to see if it is circulating inside the radiator. Use a rag to squeeze - its hot.
It then settles down and you can see it circulate in the top of the radiator - top off again and check the overflow bottle and top that off to the proper level.
I admit, the first time I put the cap on, then did it again and only one small erruption occured. No more air pockets...

wait the nose is pointed up or down?

white smoke...wouldnt that indicate a BHG? you shouldnt have to top off your coolant before every drive...

Sorry Bumpin -
Front end up. From what I read, an air pocket can get stuck under the water pump and under the thermostat, putting the front of the vehicle up helps this? Anyway, it worked for me.

okay, its been awhile. I did what you said for getting rid of air pockets and it worked great for a few weeks. However, about every 2 to 3 weeks i run into the same problems again. Why do i get air in the system. HG? Cracked head? Not sure. I have no oil in coolant and no coolant in oil and i only have white smoke for a short period when things are overheating. After the last bleed it's been fine for almost 5000 km but i'm just waiting for it to go again. Any ideas?

Burping the coolant on the 3.0 is actually quite hard cause you have to get the front end so high up.

Here is what I do:

http://www.4x4wire.com/forums/showfl...t=1&PHPSESSID=

i can get it to burp but i'm wondering why i keep getting air in the system every few weeks. Thanks for the link though.

You have a coolant leak somewhere. Start the truck up and have buddy hold the engine at 4k rpm and you get your ass under there and look for any drips. High RPM will pressurize the system so a smaller leak will hopefull show up.

Have a shop test the coolant for exhaust contamination (rule out HG)

My advice.

you can also use a pressure tester on the system to find leaks. If you keep getting air there is probably a leak, or its burning. Does the coolant recovery tank end up empty or no?

I had the *same* symptom on the 1990 V6 that I owned.
As it turns out the water pump was failing.. The bearing on the water pump was starting to fail. It'd get stop turning and then suddenly start again.
No noise, no real notification.
Check the easy stuff first, of course...

the recovery tank always empties and the coolant level always drops to just under the opening(about a half inch) at the top of the rad. once its there it doesn't really go anywhere for weeks. no signs of leaks what so ever.

Maybe you have a bad rad cap. When under pressure it lets too much coolant out.