GM 3800 Series II coolant loss - but where?

[demarpaint]

This brings back a funny memory I have helping my FIL with a 4 cyl K car that had a coolant leak. We looked high and low, then I suggested the pressure tester [that is one tool that has saved me a lot of time finding leaks over the years]. Anyway I put it on the radiator and started pumping, the car held pressure for a short time and it slowly started dropping. Great we have a leak, where is it? We had no AF in the oil that we could see, and nothing external. I said lets pull the spark plugs. I took out the first 2 plugs, on the third plug I got a face full of water. I removed the plugs with pressure in the cooling system, had I relieved the pressure we might not have seen the water.

The only thing I could think of as to why we saw on AF in the oil was because the leak was very slight, and the engine was either burning it off in the cylinder or blowing it out the exhaust. This was before the UOA days, so checking for AF in the oil wasn't as simple as sending a sample off to a lab.

 

[mrsilv04]

Just read the results of the UOA from Blackstone, sent via email this afternoon.

Wherever that quart of Dexcool went, I still haven't figured it out.... but it isn't in the oil.

This was on Platinum 10w-30 after 5,200 miles, no oil added.
Oil filter - AC Delco (non-ecore) oil filter
Air filter - AC Delco air filter.

Here's their comments:

Quote:
Everything looks good in this initial analysis of oil from your Park Avenue's 3800. Universal
averages show typical wear levels for this type of engine after about 4,700 miles on the oil. This oil was
used about that long and metals read in line with levels in the universal averages file, which suggests no
problems brewing inside this engine. The low silicon and insolubles show sound air and oil filtration, and the
slightly low viscosity isn't a concern at all. Some viscosity shearing is often a normal find. No coolant or fuel
found. Nice report at 75,950 total miles.


Considering the known issues with this engine, I may continue to do UOA's on it. The oil is changed in this car twice a year.

 

[Drew99GT]

If you have the time, try pulling all the plugs. It's a pain to get the back 3, but it can be done. Perhaps that might indicate a head gasket leak that's leaking right into a cylinder and the coolant is getting burned, hence no drips or puddles and none in the oil.

Or maybe try an exhaust gas analyzer at the fill neck of the rad to detect any exhaust that's leaking into the cooling system.

 

[mechanicx]

What was the sodium level in your UOA? You could still have an external intake manifold leak, but I think you said you saw none. Your manifold can also leak internal into the intake, but seems like that would show up in the oil.The waterpump weep hole and the heater core are about the only other likely culprits.

Sometimes the nonpressurized reservoirs evaporate some coolant away, so maybe you don't really have a leak. I would get a coolant pressure tester like DemarPaint mentioned and see if system holds pressure.

 

[ls1mike]

I had a 98 Bonneville that was losing coolant. I would have to add some to overflow once every 2 weeks I couldn't find the dang thing. It was leaking past the upper radiator hose hose clamp to the thermostat housing(factory clamp). It would do it after I shut it off and went inside, by the time I would come back out in the morning it would be gone. It finally got bad enough that immediately after driving you could pop the hood and see it.

 

[highmilegeguy]

I had a leak in my 96 riviera with the 3.8 engine.

First I pressure tested it and found it was holding pressure. So I put it back on watch since no leak was initially found,
even though I had noticed the coolant resevior level dropped a bit.

A couple months later I noticed the level had started dropping again so I went to AZO and rented the tester again.

This time I actually heard the leak under the upper intake manifold. I took off the vacuum hoses on the throttle body and there the sound was clear.
It was a leak around the EGR stovepipe. Very common area to leak at.

The moral of the story is that leaks can happen and then seal themselves up, at least in the short term. If you notice a drop and still can't find it, even with pressure testing, keep a close watch. It'll reappear. Leaks can be kind of devious that way.

 

[HyperJinx]

Can you smell coolant in the engine compartment after you drive it? I have seem those "weep" coolant from around the water pump area and heat from the block evaps it.