Coolant loss - can't determine source

[milty]

Yesterday I noticed my overflow tank was empty - I checked my radiator and it was down about 2 to 3 cups of collant. I filled the radiator and overflow tank and ran engine until I could see flow through the radiator. I capped the radiator and ran the car for about 20 minutes. I could not detect any leaks at the radiator, hoses, heater core, temp sensor, or anywhere around the engine. No weep hole leaks. Oil looks clean - no water. No green fluid on the ground. I do not smell collant outside or inside the car. The exhaust does not blow white smoke. I assume my next step is either to rent a pressure tester or take the car to the shop to have a pressure check done. I am really hoping its not a blow head gasket, or intake manifold gasket. I drove the car to work this morning - temp gauge normal. Trip is an hour on the highway. I popped the hood and the overflow tank is empty. I did not uncap the radiator. Engine has 139000 miles on it. I'll check the level at lunch time.

Do you guys have any other thoughts on my loss of collant?

[J Wikoff]

The most likely culprit, if there's no signs of leaks, is the LIM gaskets allowing coolant to leak into the intake ports and it gets burned off. You can pressure test and/or pull the spark plugs to test. Any plug burning coolant will have white/grey crust on it that other spark plugs do not. Head gaskets aren't impossible, but are unlikely.

LIM gaskets I could do in a couple hours.

[milty]

I'll pull the plugs after work - once engine cools - are any docs available for the LIM gasket replacement?

[1fatcat]

Check the techinfo link on the top of the page, just below the banner.

[milty]

I found the doc - thanks - I'll let you guys know the results once I pull the plugs.

[milty]

I found the doc - thanks - I'll let you guys know the results once I pull the plugs.

[J Wikoff]

The one in techinfo is for a Series II. While it's similar, there are some marked differences. I can outline them for you when I get some time later.

[GM Collector]

Here is a PDF showing intake manifold gasket replacement for all 91-97 engines. Scroll through the PDF to find your engine.

http://www.mediafire.com/download.php?yju4itjtrzz

[RJolly87]

Other points to consider is it is possible the coolant bypass system is leaking. The leak would only be present when the car is starting to warm up, but the thermostat is not open yet. When the thermostat opens, the leak stops. It is often overlooked. The plastic nipple likes to crack and break, not to mention the bypass hose is often forgotten. To get to and see this stuff easily, the alternator has to come of normally, but you can see the leak if you are watching for it after a cold start with everything in place.

[lackawanna1701]

Im having the same problem with my 93 SE... I cannot find the leek. Im almost convinced its the intake gaskets... pep boys quoted me 465.00 for upper and lower.. Im unsure if I could repair this myself!

[J Wikoff]

Don't be worried. Just dive in. It's a little intimidating if you haven't done this kind of work much, but that fades quickly.

My two suggestions are:
Drain the coolant to a level below the heads so you don't spill coolant into the lifter valley.

Be very careful if/when you are removing temp sensors from the LIM. Slipping a deep well socket over them is a good way to break the connectors off. Good thing they're cheap though.

I haven't forgotten about the article differences. I just didn't have the time last night.

[milty]

I pulled all the spark plugs and they are identical in appearance. I checked the bypass hose as mentioned above - it is not leaking. I did find two leaks in the overflow tank hose that runs behind the battery heading to the radiator. I have replaced it and so far no other leaks or loss of collant from the overflow tank. Keeping my fingers crossed - I'll be taking the car on the highway tomorrow heading to work - I'll post an update.

Questions - I have a 93 - haven't looked real close but the plenum/upper intake manifold appears to be metal - I thought some of the years were plastic?

[RJolly87]

Some did get plastic. If it is grey, it is metal, if it is black, it is plastic. I have the plastic on mine.

[J Wikoff]

Late 92's were updated with the plastic, so your 93 should have the plastic as well. Do you have an EGR valve perched on the right hand end of the front head, with a tube running down to the front exhaust manifold, and another tube running up to the upper intake manifold?

[milty]

Yes, I do. Is it your recommendation that since my car has 135,000 miles on it as a preventative maintenance I should replace the UIM and LIM gaskets and plenum? Or should I not fix what isn't broken?

[RJolly87]

The series 1, as was said, is not as critical as the series 2, however it is recommended those gaskets get changed every 100k miles or so anyway. It can't hurt anything, as long as nothing gets broken, and the plenum is a little stouter too. If it looks okay, no cracks or faults of any sort, I see no reason not to keep it.

[J Wikoff]

I can't remember any Series I UIM failures. The gaskets can still eventually fail though.

[milty]

thanks for the info