A quart every 400-500 miles is pretty much the same symptoms I had with a LIM hole. If you've got the CEL coming on, you almost are certainly burning coolant in small quantities. Not enough to make the exhaust smell to most people, but enough to cause misfire or knock problems, triggering the CEL.

Do the lower intake.

As said above, I'd be willing to bet the CEL is an internal coolant leakage-caused misfire, probably on cyl 6 and/or 4. Get your hands on the scanner if you can, and check that out.

If you want to get those LIM gaskets done for $500+, call a shop or dealer. If you want to get 'em done right for like $100 in parts and fluids, 3 hours, and some beer, shoot me a PM

But don't delay...all the while you ingest leaked coolant through those LIM gaskets, you run the risk of contaminating your engine oil with coolant and causing serious crankcase bearing damage.

EDIT: sorry, double post

I hooked up the scanner today, thanks to Chris for making up the adapter cable and shipping it quickly. Excellent workmanship on the cable which arrived today. After setting up the scanner, i read the codes; but none were found. More and more it looks like the intermittent check engine light (CEL) is due to a coolant leak in the LIM gasket.

I've got a new APN upper manifold this week, but the gaskets from GM-Direct weren't shipped because the VIN on our 95 didn't match their off-line catalogs for the new LIM gasket with the aluminum frame. I plan on running Dex-Cool compatible phosphate free anti-freeze in all our cars, no point in not upgrading to the newer gasket if possible.. Is there any reason the newer LIM gasket would not fit/work on a 95 SE? I played phone tag with GM-Direct for almost a week on this issue, we finally agreed to cancel the order today.

I planned to replace the O2 sensor, the coolant temperature sensor, the injector O-rings and the coolant elbow while doing the LIM gasket and installing the APN upper manifold. I know the recommendations are pretty strong on using GM parts for the O2 Sensor and the LIM gasket and at this point I am willing to pay dealer prices for those two items if the rest can be had at Napa, Kragen, Autozone and will work as well. The only O2 Sensors in stock locally at those stores are Bosch, couldn't find the Denso sensor.

Recommendations?
-sp4149

Get your front O2 sensor from Rock Auto:
http://www.rockauto.com/catalog/raframecatalog.php
DENSO Part # 2344012 , $34.79; or,
ACDELCO Part # AFS75 {#25312184}, $46.79

Note: search this site and you'll probably find a discount code for Rock Auto

You can get the aluminum LIM gasket set from either:
http://www.zzperformance.com/grand_p...ducts.php?id=0
http://www.intense-racing.com/
(search these vendor sites under "gaskets" and you'll find them for about $50)

Note: The only difference between the 1995 and the later years on the LIM gasket set is that the later year engine block has locating holes for pins in the side seals. All you have to do is snip off the plastic pins on the side seals and use a little extra RTV.

Question: what makes you think your coolant temperature sensor needs replacing? IMO that'* a pretty bullet-proof part (unless you've broken off the plastic connector...)
If you really need that sensor, post in the Wanted section and I'm sure someone here can get you one cheap.

The temperature gauge is reading low after warm-up, say 150 degrees and much lower than it used to. I'm thinking the thermostat right above may be stuck open, but even then the coolant temperature wouldn't be so low. I figure while replacing the thermostat, do the sensor as well, it'* a $20 part. A few months ago I replaced one on my wife'* early 944 where you can't get a wrench on it and it'* covered by the headlight lift mechanism. I also replaced a radiator hose and tried for a couple of hours to get the thermostat out, but failed. By comparison on this engine those parts just beg to be changed. On the 944 it is a temperature switch that controls the fans, while it sounds like on the 3800 engine it is a temperature sensor that produces a signal in response to coolant temperature, much like a pilot generator in a furnace. Build-up on a pilot generator will reduce output voltage; maybe the same thing is happening with the coolant sensor and the result is a reduced reading on the temp gauge due to a lower voltage produced by the sensor.
I'm sure there are other things that could cause a low reading on the instrument panel temp gauge, including oxidized connectors on the instrument cluster. I'm open to suggestions. For me changing the sensor is a lot easier than dealing with the instrument cluster; I always seem to have to pull the steering wheel and defeat the air bag circuit, that'* a lot of work. But I also have found that exercising the connectors increased gauge readings and illumination on the instrument cluster.

-sp4149

Sensors can go bad, however the typical fix for not heating up is replacing the T stat.

And if the car never warms up, you will have a gross polluter on your hands.

Well, I'll be darned...the ECT sensor is pretty cheap at Rock Auto:

ACDELCO Part # 21377 {#25037332}, $13.94

That would be me. So far we have identified several possible problems putting this car on the gross polluter list:
massive vacuum leak - Vacuum line to HVAC air distribution severed
leaking LIM gasket triggering intermittent CEL
low engine temp
plus possibly original O2 sensor.

Since the leaking LIM gasket needs attention first, my thought was to replace the ECT and thermostat at the same time. I really don't know if I have a stuck thermostat or a bad ECT sensor; but they are cheap parts and it'* a lot easier to replace them as part of the LIM job than later.

On other lists thermostat brands can generate heated discussions, any brands recommended? or ones to stay away from? I used to buy only brass construction versions, is this still recommended?

TIA, -sp4149