hey guys so my 4 runner has had problems with overheating for a while. First it was a bad radiator cap so i replace it and then after the radiator developed a small leak.

i replaced the radiator a couple days ago and have burped the system 2-3 times

so when i burp it and idle it w/o the radiator cap on it hold temp in the middle of guage fine.. but when i put the cap on it will slowly overheat.

is this because of the radiator cap or is it a problem somewhere else?
this cap is about 1 years old.

ive searched and no smoke from the exhaust or oil in coolant so im pretty sure my hg is ok.

what really stumps me is that it overheats with the cap on.. and it seems that one side of the radiator gets hotter with the cap on but with it off it seems even heat wise.

 

Might want to put a pressure test gauge on the radiator and see if the system is holding pressure OK, if there is a high pressure leak or if the system is over pressuring from and exhaust gas leak into the cooling system. Might also have the radiator rodded out so see if it is partially clogged.

 

hmm do you have to get a pressure tester at autozone? does this require pulling the rad?

dont think this rad is bad tho since it is brand new. it just seems that the cap isnt letting the coolant circulate while its on?

anyone ever hear something like this?

 

Something like this:
- http://www.autozone.com/autozone/ino...tingAndCooling

How-to:
- http://www.cdxetextbook.com/engines/...gpressure.html

You could see if it is a pressure related thing, because there should be no significant pressure building in the system with the cap on until you start getting up over the boiling point. So you could see if it is "pressure rising then temperature rising" (not normal) or is it "temperature rising then pressure rising" (normal).

 

thanks. i will be doing this tommorow and posting an update. hopefully this can tell me something..

 

Try a new cap. If the cap isn't relieving the pressure then essentially the system becomes a pressure cooker.

 

so im not able to find a pressure tested that in my radiator's neck size which was really wierd. they were all 1/2 inch wider at the neck. but i did buy a napa radiator cap to go with my napa radiator and now it slowly overheats when just idling but goes down when you give it gas/start moving.

is there still air in my system? i burped for at least 15 mins a couple times

 

If it overheats sitting still, check out the fan clutch (if you have the stock setup):
- http://www.barneymc.com/toy_root/techneek/fan_clch.htm

That is what keeps air moving through the radiator when you are stopped. Maybe the clutch is not locking up, could be the bi-metal spring is not rotating the shaft in the middle. I found on mine I had to use a pair of pliers to free up that shaft as mine was sticking a bit. You can also put in a thicker silicone oil to make the clutch stiffer:
- http://www.4crawler.com/4x4/Docs/FanClutch.pdf

 

hmm but wont the fan spin faster/slower based only on engine temp?

the engine temp is going down when i rev it at a stop and the fan clutch from what i read isnt affected by engine speed.. its something else no?

 

Fan has a fluid filled clutch that has a bi-metal spring that turns a shaft that controls internal valving. It is supposed to sense the heat of the air coming through the radiator and as that temperature rises, the spring twists the shaft and that makes the internal valve close making the clutch stiffer. So if all is working right, the fan will pull less or more air at a given RPM depending on how cool or hot the air through the radiator is.

And with higher engine RPM, the clutch will spin faster, but the fan may or may not. When it is loose, the clutch pumps the silicone oil around inside and the fan has very little torque and moves very little air. As the spring turns the shaft, the valve closes down, making the clutch stiffer and thus the torque to the fan is higher and it'll spin faster and move more air at a given speed. In a vacuum, the fan would spin the engine speed, but in air, the faster the fan spins, the more air it moves and the more drag there is on it. So with a loose clutch, the fan spins slow and with a tight clutch, it spins faster.

Bit if the clutch fluid has leaked out or is too thin or the spring does not twist the shaft, the clutch is loose all the time, so never locks up and pulls lots of air. So you need to check and see if the fan actually moves sufficient air when stopped, can be done as noted on the link above, basically with a thin string to hold the fan still then see if it'll lock up and break the string or use a shop rag to see if you can stop the fan. It'll either be good or not, if not fix or replace, if good, it is something else.

 

hey guys sorry for the late update but its been working perfectly now

lesson learned here is use the right radiator cap with the right radiator. had a huge headache with this because i thought oem cap would be fine on a napa radiator.

also toyota systems take a lot of effort to rid air of completely.

BIG THANKS for 4crawler and rerun for fast replies and a solution.