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Engine Still Running Too Cool

arrowshooters

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arrowshooters Enthusiast

arrowshooters

Posted
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A few months ago I replaced the 5.7 in my 98. Everything is new from the radiator back. Since then the temp guage will raise to 195 when warming up then drop to 165 and stay there. I have been through three 195 degree thermostats, the latest is a top of the line Stant. All did the same thing. I even put my old one back in and it went up to 210, like it used to, but then it would also drop to 165 degrees.

 

I have spent a lot of time reading about how it could be the guage or the sending unit, even "that's how the thermostat is supposed to work". Also, the best check would be to hook up a scanner and read what the temp is, but I'm too cheap.

 

Today I used a tempertature probe and held it to the thermo housing with the engine warm and running. I'll be darned if it didn't say 163 degrees.

 

So what's next? Is the new Rad working too good with out any clogged tubes? Hate to think I'm going to have to go the NASCAR route and duct tape my grill. LOL

jro909 Senior Enthusiast

jro909

Posted
Posted

you going off the temp guage or the performance of the motor? your guage might be broke...or off

thearborbarber Enthusiast

thearborbarber

Posted
Posted

He checked the temp with a prob that matched the temps his gauge was reading.

 

To the OP you have 2 simple options. Change the thermostat with a new 195 degree unit or live with it. The engine will still go into close loop at 165 degrees. Your rad is not the problem because the stat should be closed not allowing coolant to flow in the rad.

dlewis1111 Senior Enthusiast

dlewis1111

Posted
Posted

So if your temp goes to 195 and then back down it tells me that your thermostats are all working like they are supposed to. Even your original that goes to 210 and then back down is good. The problem is not your thermostat. You either have an over efficient cooling system or something is not letting the thermostat close when it cools down. Is your heater valve stuck open? Does it stay at 160ish during all driving conditions? What does it do when you turn on the AC? Did you swap in a gigantic aluminum radiator in place of the crap factory version? Do you have a clutch type fan or electric? And is the fan clutch bad causing it to pull air all the time, or is the electric fan running all the time. Just my random thoughts. You said you were too cheap to plug in a scan tool and check the temp. -- you weren't too cheap to drop in a good dime for a new motor, so why are you now? I would want to know exactly what the system thinks my temp is as part of the puzzle to fixing this problem.

arrowshooters Enthusiast

arrowshooters

Posted
  • Author
Posted
So if your temp goes to 195 and then back down it tells me that your thermostats are all working like they are supposed to. Even your original that goes to 210 and then back down is good. The problem is not your thermostat. You either have an over efficient cooling system or something is not letting the thermostat close when it cools down. Is your heater valve stuck open? Does it stay at 160ish during all driving conditions? What does it do when you turn on the AC? Did you swap in a gigantic aluminum radiator in place of the crap factory version? Do you have a clutch type fan or electric? And is the fan clutch bad causing it to pull air all the time, or is the electric fan running all the time. Just my random thoughts. You said you were too cheap to plug in a scan tool and check the temp. -- you weren't too cheap to drop in a good dime for a new motor, so why are you now? I would want to know exactly what the system thinks my temp is as part of the puzzle to fixing this problem.

 

LOL I'll start from the Bottom. Too Cheap because I shot my wad on the motor and the "war departement" has me on a tight leash. Stock mech. fan and clutch which breaks loose after a minute or two down the road. Single tube/stock type rad. Haven't ran the AC so can't answer that one. Yes it stays 160ish all the time after warm, under all driving conditions. Think I got it all. :thumbs:

GPSilverado Enthusiast

GPSilverado

Posted
Posted

OK, I'm just thinking out loud here. I know some of these things have already been covered.

 

If the temp goes to 195, then starts to cool, that indicates that the thermostat is probably OK (especially considering how many thermostats you have tried).

 

IMO, since the temp isn't getting too hot, it pretty much rules out the radiator having anything to do with this. A proper cooling system could maintain 195 with a 50 gal radiator, since the coolant isn't moving without the thermostat letting it through.

 

There are a couple things that I thought of here. If there is a bypass in the system somewhere keeping the thermostat from being able to regulate flow, it could keep the system from reaching the proper temp, but I don't know how it would be reaching the 195 initially before cooling back off. I would check to make sure the heater hoses are connected to the proper place for the type engine you are using.

 

The other question I have would be a water pump that is pumping too much coolant, but there again, the thermostat should hold it regardless of how much water pressure is trying to push through.

 

What happens if the thermostat is installed backwards? It may still open up, and once open would have a hard time closing back up against the flow.

 

Some of this may not be correct in my thinking, but those are the things that come to mind right away. Maybe my thoughts will trigger someone else with the answer.

clemsonblozz Enthusiast

clemsonblozz

Posted
Posted

you can't have an over efficent cooling system.. The engine circulates coolant within it's self until the temp gets to the t-stat rating, and then it starts to open.. The t-stat will be fully open about 20 degrees above the rating..

 

If the t-stat is backwards,,, it will overheat,, as the thermal part would be towards the radiator..

 

Try a mechanical gauge.. Temp probes are made to really measure liquids, not a contact type application..

 

Gotta step outside the box on this one..

GPSilverado Enthusiast

GPSilverado

Posted
Posted
If the t-stat is backwards,,, it will overheat,, as the thermal part would be towards the radiator..

 

Try a mechanical gauge.. Temp probes are made to really measure liquids, not a contact type application..

 

Gotta step outside the box on this one..

 

 

I agree with you. I wasn't sure if the engine could get warm enough for the hot coolant under the thermostat to heat the water on the top side enough to get the thermostat to open. If it could, then it might cause something like this. In fact the thermostat would open at a slightly lower temp at the spring when backwards due to the water pressure trying to push the spring, but I doubt there is actually much pressure there, ,maybe 2-3 psi I would think.

 

But I am with you on verifying that the temperature is accurate. If there was a laser thermometer available, I would use that to check the temperature of the heads and the water outlet.

arrowshooters Enthusiast

arrowshooters

Posted
  • Author
Posted

Looks like I got some brain scratchin' going on here. I thought that since the "probe" was essentially getting the same reading as my guage at the same time it would be good. I think I can get a Laser Temp gun at Harbor Feight for about $20. Should be acurate anough to get a good idea.

Rat4go Enthusiast

Rat4go

Posted
Posted

Hmmmm....seen temps cycle between 200 and 165 before with a thermostat that was supposed to but didn't have a small bleed hole it it to let air thru and to flow some water near it so it could regulate, but never one that peaked then fell to a constant low level. How confident are you that all the air is out of the cooling system? I've seen trapped air do strange things.

 

Good luck and let us know what you find!

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