81 sr5 pickup, 22r...still working on getting the carb tuned up proper...in the meantime, i noticed that after i start it and let it warm up, it starts to blow coolant into the overflow reservoir, and the upper radiator hose feels VERY firm...i don't ever remember having this issue before. I checked other threads, couldn't find anything...could it be something as simmple as a thermostat?

 

Sounds like you don't have an OEM two stage thermostat. Good info here:

http://www.4crawler.com/4x4/CheapTri...tml#Thermostat

 

I would pressure test the cooling system. Put a gauge on the radiator and see if it is over pressuring. Could be the radiator cap is worn out, letting coolant out to easily. Or you may have exhaust gas leaking into the cooling system and over pressuring it.

 

Didn't know oem called for a two stage thermostat...I literally just got home from the parts store, I figured ten bucks was nothing if it wasn't the problem...or money well spent if it was. How can you tell if its 2 stage?

 

Two valves. OEM thermostats are far superior to any aftermarket brand and they're only a few dollars more.

 

4crawler...overpressurizing is really only caused by one thing, a head gasket, right? I'm new to 1st gen yotas, but I've been wrenching a long time.

 

Typically that is the cause. If the pressure rises due to heat then that is normal vapor pressure. But if the temp. goes up before the coolant gets hot, especially if it rises and falls with engine revs/load, then it is likely an exhaust->coolant passage leak. You can also pick up a chemical test kit at NAPA to check for exhaust gas contamination in the coolant for around $20. Might also be worth pulling the t-stat and drop it in a pot of hot water on the stove and see if/when it opens, use a candy thermometer to check the opening temp. I always test t-stats prior to installing them.

 

Ok folks...I'll try that and post the results. Thanks for the tips. Good idea on testing the new t stat, 4crawler...just did a tune up on a 96 exploder, started running terrible soon after...7 days of scratching my head, 2 o2 sensors, and a sledw of other attempts later, I find out its a faulty brand new plug. Never take new parts for granted.

 

Yep, in my book "new" only means a part is not used, says nothing about it being good or not. Have run across a few faulty "new" t-stats in the past. I usually throw the old one and the new one in the water and test both side by side. I've even put the old t-stat back in when it tested fine and the new one would barely open, for example.

 

true dat ... I have run into this issue meny times .. test the thermo , just makes sence to me



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I had the same problem a while back. The head gasget was the culprit. small hole between cylandar and water jacket pushing air into the cooling system. Good luck!

 

Ok, some jackass put the thermostat in upside down...I replaced it properly but am still getting serious pressure in the upper rad hose...my head gasket kit should be here tomorrow. Going to do that. I've heard of reverse flow engines, but this isn't one, is it? Will update as I build...and thanks again.