Cooling System Question

85TrailRunner

85TrailRunner

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Joined
Mar 16, 2007
Location
Monroe
I've got an '85 4Runner that I beleieve to be overheating, I've never done any work to the cooling system so theres no telling how old some of the components are. The temperature gauge inside always reads a little under the halfway mark even after its ran for over an hour, is that normal?

Only reason I think something is wrong is because sometimes when I let it sit & run after 30 minutes or so you'll hear the coolant in the radiator boiling & even the overflow reservior will be very hot, that happened this this past summer. Yesterday I drained the coolant from the radiator(which quite possibly could be the orginal radiator) & refilled & let run for 30 minutes with the radiator cap off & every once in awhile coolant would overflow out of the radiator but then it would stop & you couldn't even see any coolant in the radiator anymore? And every few minutes a little steam would come up from the radiator? Am I not getting good coolant flow or is the thermostat sticking?
 
The first thing I would do is verify that your gauge is reading correctly and that there is no air in the system. Sounds like you may have air in the system.
 
I used a funnel that attaches to the top of the radiator so I was hoping that would have gotten the air out of the radiator while the engine ran. How could I test the temperature switch/gauge? Think the gauge could possibly be sticking when it reaches that certain point?

Also, sometimes when I turn the key to "key on engine off" position the temperaure gauge will go to the highest position that is always goes to as if the engine is warm(a little below half) & stay there even though the engine hasn't been started in days, but other times when the engine is started it starts out cold & makes its way to the highest position it'll ever read like it should.

Any ideas?
 
Regardless of whether or not your gauge is reading correctly, you should not hear boiling in your rad. Another possiblility, is it boiling or air bubbles? BTW, a funnel will not prevent air from being in your system.

When you run the engine with the cap off, you need to not let the coolant level get below the top of the rad core. If it overflows and you dont keep the rad full, it can potentially pull air into the system. To assist in the escape of air, you can jack up the front some so that the rad is a few inches higher.

You should notice flow through the rad when the temp gauge gets close to operating temp and the thermostat opens.
 
I haven't actually heard it boiling since this past summer when it was 100* outside & it probably had more water than actual coolant in the system & I believe the coolant level was low back then also, I've since drained & filled with non-mixed coolant.

I ran it for a good 30 minutes yesterday with the funnel on top of the radiator with it full of coolant ready to go into the radiator so its not getting ran with the coolant level falling below the radiator core & it quit air bubbling after a few minutes but still a little steam at times. When it stops steaming you can increase RPMs for 5-10secs & let off & it'll steam a little again. I can see the coolant moving through the radiator. I also noticed that after it runs then shut it off it'll put coolant back into the funnel. Even without the funnel & the radiator cap on it'll force coolant out the radiator cap.

I'll try jacking up the front end to help. Is it the top radiator hose that should be hot & the lower hose cool when the engine is running & warm?
 
85TrailRunner said:
Is it the top radiator hose that should be hot & the lower hose cool when the engine is running & warm?
Click to expand...

Yes, that is correct.

In regards to the coolant level rising after shutting the engine off, I *think* that happens because the engine is still heating the coolant (because it's still really hot) and the coolant is expanding. There is no coolant or air flow to remove heat from the system, but there is still heat added to the system for a short period of time.
 
:confused:If none of this works then it could be a blown headgasket or cracked head....but think simple to complex
 
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