elvisizer

so, about once a month I have to top off the coolant tank. The engine is not leaking coolant anywhere, and there is no evidence of coolant and oil mixing when you check the dipstick and the cap on the coolant tank. My first guess is that the coolant is getting into the combustion chambers and burning up, since there's no evidence of it anywhere else. There's no white smoke from the exhaust though.
Would a leak down test tell me more?
It has been about 180,000 miles since the head was replaced, bottom end of the engine has about 230,000 miles on it. I had a compression test done as part of my PPI last year, and one of the cylinders was about 20 PSI less than the other three, which isn't good . . . . .
Is it time to rebuild the whole thing? or just the head?
Are there any other diagnostic tests I could do (or have done) that would narrow down what's actually needed?
maybe it's time to get a little loan and get a 951 instead . . . . . . .
hard to decide . . . . . .
any advice/ideas appreciated . . . . .

elvisizer

Luis de Prat

Have you ever replaced the expansion tank cap? It's supposed to hold a certain amount of pressure to prevent coolant vapor from leaking out.

elvisizer

no, i haven't. that's an interesting idea. would a month be enough time to leak from the full line down to the minimum line?

Flight_951

The full line is actually the maximum line. When the car is cold the level is at the minimum, or near there. When the car is hot the level goes up to the maximum line, or near there. Are you filling the car to the max line when cold?

Luis de Prat

If you take out the cap and look at it, you'll notice it has a built-in spring and rubber flap. If it's the original cap on the car, it's likely that the flap has lost sealing ability and is letting just enough vapor out to lower your coolant level over a month's time. BTDT.

Big E

I had the same type of problem - coolant seemed to be disappearing, but there were no leaks that I could find, no puddles, etc. Just magically disappearing. Expansion tank cap fixed it. My cheapest fix ever!

Devia

Luis, if that spring is weakened, can it let water pour out!?

I had a nice little waterfall over my coolant tank last night, from under the cap. Trying to figure out if it's the cap, or the waterpump.

She didn't overheat in traffic, no water anywhere, until I shut OFF the engine!

After the water quit pouring out, I discovered the cap was loose.

Any ideas?

Peckster

Cooling system pressure often peaks right after the engine is shut off, the heat from the cylinders is still travelling through the metal to the coolant, but the coolant isn't circulated through the rad to carry the heat away.

Many cars blow weak hoses a minute after they've been shut down.

If your cap was loose, it's probably not a problem.

elvisizer

flight_951, yeah, i've been filling it when cold, but not up all the way to the max line.
i think i'm going to check the cap. might as well give that a try.

Devia

Peckster, that's something I didn't know, about the heat temperature peaking after it's turned off. Usually my cooling fan will kick in, until cool enough to touch.

It is possible some moron thought they'd check my coolant at the garage, when I wasn't looking, freaked when he saw the oil floating in the tank, and didn't screw it back on right.

But the 225s look better in the wheel wells!

- Julie

Granite 944

If you have access to a coolant pressure tester, you can check the expansion tank cap, and manually pressurize the system and see if it holds pressure (no more than 15lbs). If not, you leave it pressurized, and start looking at all the hoses, waterpump area, heater core, and you may very well find the leak, if it is an external leakage problem. I'm betting on the cap being no good. I purchased a tester, for the same reason, and it also works very well for bleeding your cooling system with. This was the only way I found out that my heater valve, and core hose was leaking. Good luck!

jabbadeznuts

Have you noticed any dead animals in your area lately?

austin944

I have a very slight leak around the gasket for the water temperature sensor that's screwed into the radiator, just need to find time to work on it and get the other car out of the garage.

I would second the recommendation for the pressure tester, it's a great tool to have. I got one at Pep Boys for $60. You may want to leave the tester on there overnight and check it in the morning for a very small leak like yours.

Devia

Only read it if I want to be a show off.

Nope, no dead animals - I watered down and washed the overflow away!

I checked from where I turned into the townhouse complex, and there was NOTHING leaking at all, not even on the freeway (in heavy traffic, I might add).

I am going to try and replace that cap first.

But she still gets a time out, after I did preventative measures on her!

elvisizer

guh? what about base 6?