Zrout

I don't think I'm an idiot, I've replaced engines, I've diagnosed dumbest weird little problems, but I don't "get" this one...

'95 LT1 - runs perfect , up until few weeks ago it would barely reach 210 degrees , usually sat at 190 all day long even on hot summer days, never have I seen it go past half on the temperature gauge

example: I can fill the system up, use the bleeder screws to let air out and everything is fine, overflow has the proper level in it, engine has coolant and "low coolant" light is off... I can then drive it for about 2 days or even 1 day and low coolant light comes on.

If I stop , let it cool and look in the radiator there is about 1" missing which makes sense, the top sensor then claims the coolant is low.

so I refill it again... and in 1 more day same thing

- engine does not smoke at all
- there is nothing in the oil
- 0 leaks, I've parked this thing on brand new pavement when hot, overnight etc... not a drip anywhere.
- both fans work
- new radiator cap too.
- it has 190,000 miles , water pump was replaced around 100k and most hoses have been replaced too due to blowing/cracking/falling apart

I think the coolant overflows into the overflow bottle but cannot come back when the engine gets cold if that makes any sense, I'm not too familiar with LT1 cooling system but doesn't the overflow also act as a source of coolant if radiator gets low (so the pressure would suck some into the radiator?)

just to complicate the matter, sometimes, like this morning I saw the temp creep up to 200-210 and I stopped at work, by the time I got out of the car the overflow was spitting coolant all over the parking lot

any help would be greatly appreciated.

shoebox

Make sure you have a good radiator cap and that the pipe from the radiator to the remote reservoir does not have a hole in it. It can leak under the battery, onto the front fascia and dissipate before it ever hits the ground.

6SpdLT1Z

I had a similar problem. My '94 Z would boil coolant out the coolant reservoir. I did a bunch of random little things and never had a problem with it again.

-Radiator Cap
-160* Thermostat
-Flush with new 50/50 and water wetter
-Tuned fans to kick on sooner

Your car is getting hot, and when it gets hot it is boiling. I'd replace the thermostat with a 160*, put in a new mixture of coolant (to ensure that your boiling point isn't too low) and pick up a manual fan switch/tune your pcm to kick the fans on sooner.

Also check the system for air (bleeder screws) and check for debris on the underside of the radiator

Zrout

dumb question, the bleed screws should only be used with the engine off right? so it doesnt' suck in more air...

showbox, thanks, I will check the hose but it really isn't leaking.

6speed - I'd go to a lower thermostat but this car is driven all year round in NE, if/when I figure out the issue and fix it I will need heat again in the winter

cap is new, I need to test when the fans kick in, I wonder if they come on too late. I found a nice instruction page on shoebox's page

shoebox

You may not know you have a hole in that pipe until you remove the battery. If there is even the smallest hole, it may allow coolant to go TO the reservoir, but it will never come back during cool down because of the vacuum leak. Therefore, you loose coolant in the radiator over time.

Zrout

good point, I will look into that.

BIG SHAFE

Same problem, I had to get a whole new battery tray/overflow tank.

Zrout

if i remember correctly it's those retarded metal/rubber hoses embedded into that battery tray right?

I'll ghetto rig it with just rubber hoses for now and see if problem goes away. I could use a new battery tray though so down the road that can get replaced.

BIG SHAFE

Yes, the metal hose can be removed I think. I actually had a leak between the tray and the tank. The plastic had a hole in it, not any of lines in/out.

SnakeOiler

I had the same problem. I replaced the overflow hose/tube and the grommet. Problem solved.