Topic: weird overheating problem

[-Matt-]

hey everyone. i have looked through many forums and even looked all throughout the Toyota repair manual and have found nothing to help me. my 85 runner has always ran a little bit above average on the thermometer (tinny bit above half way) when i first bought it the engine was blown and was full of corrosion. i replaced the engine with another very clean/runs awesome engine, i used the same radiator since the guy had just replaced it thinking it would help the blown engine and it was still good and clean. after i replaced the engine, the gauge would do weird things every so often like rise up fully in the red for probably 1 minute and then drop back down to half way. (thermostat opening and closing). i let it go for it only did it once every now and then. thinking maybe it was my thermostat or radiator i replaced both and it did nothing at all. my heater core was a POS ever since i have owned it due to the buildup in my old engine, the other day it finally stopped working to i decided to replace it. after doing so the problem with the gauge going in red and then dropping got worse. which doesn't make sense since it should be the other way around. (but the heater works great and burns hot as hell) it doest it all the time now just driving around town. i thought that it could be the thermostat so once again i replaced that and again it did nothing. today i decided to take my top radiator hose off and flush my system. i noticed that the engine would start to get hot and the thermostat would open-releasing a good amount of water. it would do this for a minute would pretty much stop flowing for a good 5 minutes. this process would keep repeating while i was flushing it in my driveway. at the time the gauge never left halfway. this doesn't make sense to me because form what i know is once it warms up the thermostat will open and will start a continual flow even at idle. i know that if your going up hills and fully getting it the flow will be heavier but i assumed that it should always be somewhat flowing. i would consider it being maybe my sending unit for the thermostat, but i felt that the probability of that went away from how i saw the water flowing , then stopping  out of the hose when it was being flushed. (which is why my gauge does weird things). i ran it around town without a thermostat and it barely even read a temperature on the gauge, so i know its not the radiator, heater core, or water pump. its just weirding me out because i have replaced 3 thermostats, one radiator, and 1 heater core. and its always stayed the same if not get worse. without it if obviously ran way to cold but with it in it does weird stuff and runs hot. i would think that this would have nothing to do with it but when i put the new engine in i put the more advanced 87 in with all the crap for California smog, but i used my old wiring harness from my 85 so it would match up and also eliminated the fancy smog crap to match up with the 85 engine. i unplugged the sending unit that it attached on the piece that hold in the thermostat and that seems to do nothing (gauge still read) so i really don't know y its even there, but the one that is sending the temp information is the one by the fuel rail that is attached to the block, it is attached by a small blue clip. iv asked many people about this and no one really knows whats up . if you have advice, tips or hints, it would be greatly appreciated.

[79coyotefrg]

that last part  ..... 

i unplugged the sending unit that it attached on the piece that hold in the thermostat and that seems to do nothing (gauge still read) so i really don't know y its even there, but the one that is sending the temp information is the one by the fuel rail that is attached to the block, it is attached by a small blue clip. iv asked many people about this and no one really knows whats up

.............

sounds like the temp sensor wire is attached to the oil pressure  sensor,  and  maybe the oil pressure guage wire  is attached to the temp sensor in the  thermostat housing

[-Matt- [OP]]

hmmm that actually is a very good idea im gonna go check that thank you, il get back and let ya know

[Tallchevy]

Replace the t-stat. When I first got my 89  with a 22re a few months ago I found the radiator was leaking. I replaced the radiator & bought a t-stat from Napa back in 10-07. The water pump went out the follwing month so I changed it but didn't do the t-stat since it was new. The engine would do the same thing your is doing so I checked for a blown head gasket & it was ok but would still get to the red for about a minute & cool down after the t-stat opened. I decided to change the t-stat again but this time I bought it from another parts store. Now the temp gets upto about 1/4 & stays, problem solved.

[-Matt- [OP]]

hmmm thanks thats interesting. i would have thought that something like that would be so simple that all new ones would work but that would completely make sense, because iv done the pinpointing and it has to be the t-stat. the new one that i just bought was a pos 5$ pep boys special.. know i know..but all i had was 5 bucks. was the good one that you picked up from napa?

[jimbo74]

is it possible your issue is temp guage overshoot?

http://www.4crawler.com/4x4/CheapTricks/index.shtml#Thermostat

[Tallchevy]

was the good one that you picked up from napa?

Nope

[WHITE_TRASH]

Why not put a GOOD temp gauge on it.  The stock ones tweak around a bit sometimes.  Put a good name brand gauge on it and see whats really happening.

[Doof]

thanks so much jimbo im almost positive thats what the problem was. before u sent the article i had the idea of drilling 2 medium size holes in excess metal around the t stat and to my surprise thats what the article recomended and that fully fixed the problem. that article helped me to much, now i fully understand what was going on thank you

[Doof]

Why not put a GOOD temp gauge on it.  The stock ones tweak around a bit sometimes.  Put a good name brand gauge on it and see whats really happening.

im gonna take your advice and get a real temp gauge better be safe than sorry thanks

[Doof]

btw that was clownman, he forgot to log off my sn and tye his in... but ye... fo sho

[Tallchevy]

Some t-stats comes with valve/breather to let the air out when filling with coolant. I forgot to mention that I used my side cutters & cut off the breather. Now I have the hole they are talking about without drilling. Also a guy that owns a radiator shop told me that the hole should point to the front of the engine.

[79coyotefrg]

that breather  shows  its a good quality tstat,  NEVER BUY A STANT

[-Matt- [OP]]

haha very good to know thanks