I have been wrestling with my LT1's coolant system (68k miles) for a while now. I've replaced the t-stat (correct 2-way extended length), two different new radiator caps, radiator, water pump, and fresh 50/50 Dexcool. I've ensured that coolant flow is unrestricted through all of the hoses and the heater core. I have followed Shoe's refill/flush procedures to the letter. I have bled this thing so many times it's nuts. I filled the water pump to the t-stat inlet and so forth. Anyway, here is what's happening...

I bled it once more this morning (I was finally able to get a nice stream out of both bleeders) and took it out for a drive. The temp stayed very normal (185*-190*) and I thought I had it fixed. I decided to shut it off to see if I would get any overflow into the resivoir. Sure enough, as soon as I turned it off coolant poured out. I turn it back on and the temperature starts rising, I limp it home. (shutting it off every now and then to ensure I don't run it with the needled pegged.) I tried to bleed more air off when I got home but all that would come out is steam, no liquid. I have read through all of the 'bleed', 'coolant', 'overheat', etc... threads. I figure my problem is being caused due to boil and have narrowed the cause to one of two things:

1) Leak in the coolant system. I'm almost positive this isn't being caused by a blown headgasket. My exhaust is normal and the oil is not milky. I do not see any leaking coolant or hear any obvious hissing in the bay. I'm going to borrow a pressure tester early this coming week to test this theory.

2) I've still got air in the system. I have bled this thing for literally hours, over and over again. I've done it the heat on, heat off, etc...

What would shutting the car off do to the system to cause it to begin overheating after a seemingly normal temperature ride? Sorry for this long-winded post but I am really at my wit's end here. Any recommendations would be greatly appreciated.

 

you dont smell it while driving?

 

No, not really. I've gotten a few whiffs, but I believe it's just burn off from where I've been bleeding it. I've checked the passenger side floor and it's dry, so the heater core's intact.

 

check for evidence of overflow on the overflow cap.

 

Sorry, I guess I wasn't clear enough in my initial post. Coolant pours out of the overflow (resivoir).

 

you must have a blockage somewhere or your cap is crap. get a GM cap, 10 bucks

 

I've tried two brand new 18psi. caps. Granted, they're not GM--I got them at Napa--the GM cap doesn't have any special characteristics does it? I'm almost positive there is no blockage, the whole system is spotless.

 

well, everyone seems to say that AM caps are worthless. looking at the GM cap that i just got today, it looks totally different...sooo...there must be a difference somewhere

 

Well the caps I've been trying are cosmetically different than the GM one. I really don't think they have any function other than to keep the system under their rated pressure and provide blowoff in over-pressure events.

Any one else have any suggestions?

 

I had the same problem, I used a rich coolant mixture this time and i've been fine since. I followed the instruction in the driver's manual, pouring coolant into the radiator (not the reservoir) little by little until i got coolant coming out of the lower bleed screw. I could nto get it coming out of the upper bleed screw, I tried adding a bit of coolant for like 45mins.

Then I started the car and poured in coolant into the radiator until its level would no longer fall. Shut the car off, put the cap on, checked the reservoir, did not need to add more, and the car has been fine ever since. I used maybe 65% coolant, 35% water, as this gives it about 10 degrees celcius more before the water starts to boil.

I have been told by a buddy that I should change my coolant temperature sensor, he says the coolant should not boil until about 125 degrees celcius, but the guage shows shows 105 and its already boiling out. Thats something i'll look into if i get coolant boiling out again.

 

I had a similar problem. My fix was the hose that connects the overflow to the top of the radiator. It is an aluminum tube that goes down into the overflow. Mine was cracked and it would overflow like a volcano. Just something to look at.


Tim

 

I'll try getting the GM cap. I've taken out my resivoir out and checked the hose, seems to be ok. I may also try increasing the coolant ratio to prevent boiling. Looks like the pressure test is my next step though...

 

Water has much better cooling properties than coolant. Drain your coolant/water mixture, run 85% water and 15% coolant and post your results.

Straight water would cool the best, but you need some coolant in the system to lubricate it and prevent rust.

Give it a shot.

Also, check the front of your radiator for leaves, etc.

 

it has better cooling properties but boils at a lower temperature.

 

curiosity question....why would the sensor have anything to do with that?