89 Silverado 350: overheating or faulty temp sensor?

[775stepside]

So I just finished the truck and I started the truck and I let it warm up, filling it with coolant as well letting all the air escape. It got up to I want to say 180-185? (Keep in mind I got a 185 tstat) so once I let it idle for about 10 minutes I drove it around the block to the front of my house and noticed the temp guage started spiking all the way to 260 or whatever it maxes out too. I drove it back to my garage and turned it off.

I put the key on engine off and the guage spiked back down to 140 or so, turned it back on and it stayed under 210? Is the reading false on these moonshape guages?

[775stepside]

This is after it got up all the way to 260 I turned the key on engine off...



Turned it off and did it again and it went back down and it stayed around 170-180 idling.

[TennesseeZ]

Get an aftermarket guage to be sure what the dash guage is doing. IIRC you can get a Sun or Autometer for probably $25, easy install and removal if you want.

[speedygonzales]

When filling the coolant, you have to top it off after the thermostat opens while the engine is running. Once it's topped off you close it up, shut it off and let it sit over night and check it next morning. If it's low (most likely) next morning, you fill it up and you're done.

Incidentally if you replaced the sensor near the thermostat, it has nothing to do with actually keeping the engine cool. I saw your other thread. In fact neither sensor has anything to do with cooling actually. The other sensor is used for the gauge. That one most likely could be the problem since your gauge is fubar. But I think you are only air bound.

Cooling is strictly mechanical. Fan, coolant and thermostat.

[775stepside]

Yes I know the guages don't keep it cool, what I was trying to say was if the guage/sensor was faulty and giving me false readings.

I did have the engine running and kept topping it off, I believe the thermostat did open because I saw the coolant significantly drop fast so I topped it off. I'll be checking it here shortly and just going to buy a aftermarket guage to make sure

[775stepside]

Hey guys so I just read on other forums about my truck getting hot, I saw that someone said that the clutch fan has little like ball bearings? I noticed one laying on the floor when I was working on my truck and I was curious where it came from? Could it be from my clutch fan? It's somewhat hard to turn by hand when engine is off? Could this be why it's getting hot?

[775stepside]

How can I test the fan clutch?

[speedygonzales]

Usually there is a lot of drag when you try to spin it. When they fail, it becomes very easy to spin by hand. If you have any doubt, compare the strength it takes to turn yours to a new one at the auto parts store.

In some rare cases, I've seen people bolt the fan directly to the pulley with a spacer to see if it then cools adequately.

[775stepside]

Ok, I was reading retarded timing can cause the engine to overheat too? I haven't got a chance either to set timing on it

[dragginmetal]

Lately mine has been doing basically the same thing, but it only gets to around 230*. I pulled the therastat and it stays around 150*. I plan to get a new therastat and drill a small hole in it. There are several threads that talk about that. Don't know if that's your problem or not. Just something to think about.

[775stepside]

I just put in a new thermostat, and before I put new heads the truck never got hot. I try to squeeze the top radiator hose when hot and it's really hard, seems like i got a lot of pressure and notice some leaking at the cap

[dragginmetal]

Well keep us updated. I'm curious to see what the problem is.

[775stepside]

Hey guys, so I just went out and started the truck, let it warm up to 180-200 and shut it off since it didn't go back down. I went to grab the top radiator hose and it's cold as hell still and there was a little steam coming out the radiator cap? Is this a bad thermostat? Keep in mind I put in a new one.

[775stepside]

Fan clutch doesn't wobble or move, I shut the truck off and the clutch fan stopped right away. I didn't replace the water pump or radiator cap. Is this a faulty thermostat I got from the store? Either way I'm going to take it apart and get it replaced

[95 S_Trucker]

The top hose was cold because the thermostat didn't open. How long was the temp at 180-200? 10 seconds or 20 minutes? Now would it have opened if you let it run 30 seconds longer? Its hard to say.

I would start it up again. Let it warm up. Shut it off if it gets too hot. But feel the upper hose when its above 200. Normal operating temp is 195-215 on these trucks

And are you using the gauge to determine engine temp? or a scanner or an IR thermometer.

[95 S_Trucker]

The only purpose to drilling a small hole in the thermostat is to help bleed the air out when filling the cooling system. It prevents air from being trapped under the thermostat

[775stepside]

I'm going off the guage from the truck, and I have let it idled before as my previous posts, drove it around my house and the temp spiked all the way up. The thermostat I got is also a 180 so it should have opened sooner. I believe it did get around 200 because it was just about to 210 halfway point.

[775stepside]

So right now when I let it warm up it was hot enough, went to grab the hose and was cold and it didn't feel like there was coolant just pressurized air

[95 S_Trucker]

Was the hose hot? Most likely the air is from not filling the cooling system completely. Did you burp the air out of the upper hose? Did you run it until the thermostat opened(with the cap off) and then top it off?



Was your cooling system in good condition? Do you see floaties and gung stuck inside the radiator? Is the coolant brown? Is there dirt and debris in between the radiator and A/C condenser?

[775stepside]

No the radiator hose was cold still, and it seems like their is small spots of oil inside the radiator when I pull off the cap, besides that the coolant is green( I put 2 gallons of 50/50) and there isn't anything between the radiator and ac. It never overheated before this.

[775stepside]

I believe the oil in the system is from when I had it apart and left the lower radiator hose uncovered

[775stepside]

So I took the tstat out and tested it, it opened, not sure at what temp. I just boiled hot water and dipped it in, but it opened to one side and not straight down? Could this cause it to not open when it's supposed too? I took pictures. Also I double checked the top radiator hose and its warm towards the tstat housing and it's cool as soon as it's by the fan shroud?

[775stepside]

Well I put a 195 tstat let it warm up turned up the heater and the tstat finally kicked in, drove it around the block and it stayed at 210 on the factory moonshape guage, got in the garage and it spiked up, gave it gas and it went back down.

[rickpilgrim]

Getting hot at idle and cooling down at rpm/speed is normally an airflow problem.
I know you checked your fan, is it in the shroud? Also have you made sure your radiator fins and core is clean? When idling warmed up with radiator cap off can you see fluid circulating? How much oil got in the coolant? Oil can coat the inside of the radiator and limit the heat transfer.
1/8" holes in the T-stat are done not only to bleed air they also allow some coolant to circulate and can help cooling. Of course in cold climates it takes longer to warm up then.
Is your belt clean and dry, in good shape? These are common things to check when servicing your cooling system.

[775stepside]

I'll take off the fan shroud and check the fins on the radiator, I didn't have a problem before this. Only think I can think of right now is to adjust timing since I haven't done that yet, it seems to idle lower then it should so if I adjust timing to idle faster it might cool better? Seems to want to hesitate when it's warm and it barely give it throttle. I'm thinking it's because my timing is off?