theluxy1

91 toyota p/u, 22re, base model. i just did a head gasket, timing chain and guides, waterpump, t-stat, radiator, and all coolant hoses except the heater hoses. fired it up, set the timing, adjusted the idle, ran it up to temp, started overheating, shut it down, checked some stuff out. long story short, napa gave me a 195 degree thermostat, which is too hot, so i got a OEM stat from rodland, and it still overheated. not while sitting in the shop idling, but when i took it on a test drive. so i brought it back to the shop, got a 180 from napa, threw that in, ran it up in the shop, temp was perfect, the stat popped at exactly half a gauge and stabilized at about 3/8 gauge. test drove it, temp stayed steady at about a quarter gauge, which was lower than i expected, but i called it good and sent it home on friday. monday the customer called, said it was overheating and had a surging idle. so i had him bring it back in, and did some more testing. radiator has good flow, no cooling system leaks, runs at 1/4 gauge sittin in the shop and 1/8 gauge on the road test with no thermostat in it. i reinstalled the original 190 t-stat that i pulled out on my initial teardown, it doesnt overheat in the shop, but it fluctuated for probably about 45-60 minutes between 3/4 and 1/4 gauge, it finally stabilized at about 3/8 gauge. i havent had a chance to test drive it yet, but thats first on my list for tomorrow. every single t-stat i put in this thing acts like its lazy.

additional info: the truck currently idles at about 1200rpm, diagnostics lead me to a bad auxiliary air valve. i currently have the passage in the throttle body plugged so that i can get the idle down to where it needs to be (750-800). i also did this exact same repair, minus the radiator and a couple of hoses, to my personal vehicle (86 toy p/u, 22re, sr5 4x4). i ended up putting a 180 degree stat in it, and it runs perfect, never overheats, gauge just south of half.

anyone got any ideas? if i cant get to the bottom of this by the end of the day tomorrow, i'm gonna rip the head back off and start from scratch. this truck hase been a nightmare for me, i have never had so many issues working on a 22re.

snobdds

The guage is not well known for it accuracy, so to find the real temp of the coolant, an IR pointer is needed. Stock thermostat should be 88*C or 193*F, so a 195* is correct. You may just need to burp the system reall well.

However, it sounds like temp guage overshoot. The return from the heater core dumps right in front of the thermostat, tricking the thermostat to close, when in reality the coolant is hot. It's a pretty common problem. Get a dual stage thermostat, part number 90916-03070. Here is some more details
http://www.4crawler.com/4x4/CheapTri...tml#Thermostat

theluxy1

i did have some question about the gauge accuracy. as far a burping the system, i use an airlift to vacuum the system down, that eliminates about 90% of the air in the system. it only sucked down about a pint of fluid out of the recovery bottle last night. i'll try that p/n for the thermostat, see what that does for me. the only issue i have with that is that when i run the truck up initially, i have the heat on high only until i get hot air out of the vents, then i shut the fan off, so the heater core isnt doing any cooling. hot water goes in, hot water comes out.

lobukbuild

were the t-chain guides all worn down? if so all that plastic goes into the pan and gets sucked into the screen, causing a clog and slightly lower oil pressure.low pressure can cause more heat. very simple fix just pull pan clean screen off ( and clean out pan ) and put pan back on with a sealer.just an idea i had. worth while to check it out. sounds like your air bound though or possibly bad clutch fan.