Cooper04

I have a 96 4runner sr5. It is a 3.4L V6. I have a problem with my cooling system. The only way the truck will not run hot is with three holes drilled in the thermostat. A normal thermostat does not work. Any one have any ideas or suggestions?

cubuff4runner

I don't understand why a new thermostat doesn't work. After reaching a certain temp the thermostat should open.

Cooper04

I have no idea. The new thermostats are not bad thermostats. They are opening in boiling water , but not in the engine ?

wimpywade94

you could have a clogged return line to the radiator, causeing pressure to build up when its hot and the thermo dosent open up soon enough, or you could have a head gasket leak causeing pressure in the system?

thats what teh problem on my 94 was.

later
wade

cubuff4runner

Where did you pick up the thermostat? I have had problems with thermostats from Checker Auto, AutoZone, etc. I would only use Toyota Parts.

protech03

As a Toyota tech I can say that all aftermarket thermostats seem to be crap. Use Toyota replacment with new seal. I have always drilled a small whole when replacing any thermostat. Reason being it greatly limits the hastles of purging the trapped air from the system when the thermostat has not opened yet. It also lessens the likelyhood of getting a "Hot spot" in the head as even with the thermostat closed there is always some flow. Third benifit is it lowers the operating temp a few degrees as well as stabilizing the temp guage reading by lessening the fluctuations as the thermostat opens and closes. The hole size should be about 1/64" or slightly less. I do not remember the exact size I use but I know where it is in my box and use it often. As stated by others...restricted radiator or head gasket problems are also a possibility and should be checked as well.

Take Care!
Brian at ProtechEZLift.com

95_4X4Runner

Also, remove the radiator, and reverse blast the A/C condenser coil and the radiator with water, to blow the built-up debris out of it. This is a common fix for 3rd Gen Supras with cooling problems.

TechWrench

I'm not sure of the specific layout of your thermostat housing, but one possible problem could be an air pocket in the housing which would prevent proper contact between the thermostat sensing coil and the hot water. Most vehicles now have a water bleed valve some where on the engine to purge air from parts of the system that are higher that the radiator and might develop air pockets. Another possibility is that someone installed the thermostat backwards by mistake or a piece of the sealing gasket is interfering with its operation. And, as others have already mentioned, it might be a problem with the thermostat itself, not all aftermarket units work as well as the original.

Good luck