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almost overheats after coolant flush

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Hey all,

Did a coolant flush on my 2000 GT this weekend, got rid of the evil orange/red dexcool and replaced with yellow/green Prestone.

Drained the system by removing the thermostat housing and the lower rad hose. Went pretty well, and have been adding coolant every morning a little bit at a time due to there being (I assume) air in the system. I do seem to be required to add less and less every morning (its been 2 days so far).

However, every morning my temperature spikes to around 100C on the gauge (212F) for about 30 seconds, at which point it drops back to normal which is around 92-95C (198-205F). After this it stabilizes and dos not overheat at all.

My theory is that there is still an air bubble in the thermostat housing, causing a flow issue as the thermostat opens.

Or it could be a defective thermostat (which I did not replace).

Will be bleeding the system again tonight using the bleeder screw on the thermostat housing.

Also may have a LIM gasket leak on the backside on the LIM. (Not leaking into the oil).

I did use 3 coolant sealing tabs as I filled the radiator.

Thoughts?
Thanks
Terry in Winninpeg
 


Did you happen to fill the coolant from the LIM first, then the rad?

Lots of time when not done that way, air pockets can form and they are harder to get out.

I'm sure another bleeding of the cooling system can surely help.
 
It probably is an air pocket trapped in the coolant passages in your block, try bleeding the system with your car on a bit of a hill or slope, front end being higher than the back, that's how I do it and I never get air pockets anymore, in spite of filling from the filler cap :D
 
Flush it again and get those sealing tabs out of there. They will do no good but to clog up your rad and heater core. You have an air bubble in the system. Open the bleeder on the thermostat housing to get the air out when the car is warmed up.
 
dsmuts said:
Flush it again and get those sealing tabs out of there. They will do no good but to clog up your rad and heater core. You have an air bubble in the system. Open the bleeder on the thermostat housing to get the air out when the car is warmed up.
Click to expand...

That never works for me.

Just drive the piss outta it and fill it as needed.

Also drilling a small hole in the t-stat is probably a good idea.

Takes a wee bit longer to heat up but helps with bleeding and prevents rapid thermal expansion in the winter when it finally cracks open.

Many t-stats used to come with a little hole with a one way valve that opens when air is below it and closes when water pushes on it. Seems its something that has fallen out of practice now though.
 


matt5112 said:
That never works for me.

Just drive the piss outta it and fill it as needed.

Also drilling a small hole in the t-stat is probably a good idea.

Takes a wee bit longer to heat up but helps with bleeding and prevents rapid thermal expansion in the winter when it finally cracks open.

Many t-stats used to come with a little hole with a one way valve that opens when air is below it and closes when water pushes on it. Seems its something that has fallen out of practice now though.
Click to expand...

I did the same thing when I replaced the LIM on mine. Drilled a 1/8" hole in the T-Stat and then filled it from the housing, topping it offfrom the radiator and finally filling the over flow. It bled itself and never had any issues after the fact.
 
On the sealing tabs,every manual (including haynes) says to use them. They are made by AC Delco, and used in the factory to address small leaks, just like I have on my LIM gasket. So why would I flush them out? Once in water, it breaks down into a fine powder, no chunks like in Bar's leak. I can't see it causing issues, especially since endorsed by GM. If it was aftermarket crap, I'd be totally with you, but I know too many people who have successfully used them to dismiss their usefulness.

But I'll bet the jap manufacturers are laughing at the fact that they have to be used in the factory... :)
 
you need to re bleed the engine.

the way i do it is to open the rad cap, let it idle till the fans come on, with the a/c off.

when the fans come on you know the t stat is open, then bleed it, top it off, cap it.

fill as needed while waiting for the fans to come on. if it burps out the rad cap hole while waiting dont worry about it.


and the way i flushed my engine was to pull the lower hose off the water pump, remove the top hose from the rad, then remove the t stat, put the housing back on with the hose on, but no t stat, put the lower hose back on the w/p, fill the rad with water, start the car, leave the hose running in the rad start the car up, now you are filling the rad with water and its pumping out all the old crap out the top hose into a bucket.

now pull the lower hose again to drain the water. put your t stat back in, hose on the upper rad. then i just dump a gallon of coolant right into the rad, and top it off with water and bleed it.

i have never pre mixed my coolant. in any car ive ever owned. it all turns green in no time.
 
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