Hi, I just bought a 1994 Buick Regal Custom with a V6 3.8 engine for my son. We bought the car from a private seller who said the car was in great shape. He had notes in his Haynes manual showing all the repairs and parts replaced and oil changes over the past 5 years he has owned the car.
Anyway we test drove the car and it seemed to run just fine. He said it would smoke just a little if it was left idling for a long time and that it had an oil leak he thought was the valve cover or oil pan gasket but that it was a very small leak.

We drove the car about 100 miles to get it home and started checking it over a bit better. Something we had forgotten was to pull the radiator cap off. When we did it was covered in a brown gunk. So was the filler neck in the radiator as well as in the tank. WE pulled the thermostat and it too had some brownish residue on it as down inside the intake was brown.

We drained the oil into a white drain pan and it looked brownish to normal with no water in it.
We drained the radiator and no sign of oils mixed in the coolant though it was brown.

We performed a chemical exhaust gs test on the radiator and the chemical turned a green to light yellow after the engine got warm and the thermostat began opening and closing. Yellow is supposed to indicate exhaust gas in the coolant. We repeated the test several times and used the new bottle of chemical as well as an old one we had at the house with the same results.

We found the coolant to be a little low once home but my son said the temperature gauge never went over 210F.

We performed a pressure test on the coolant system and found coolant leaking out between the lower intake on the back side by cylinder 6 as well as coolant seeping out from somewhere under the throttle body. WE could not see under it but could see it where the lower intake meets the block. If I understand from my research that is a common failure on the 3.8 v6 engines.

Nest we decided to do compression and leak down tests. We ordered a OTC leakdown tester from the parts store and already had a compression gauge. The first results were somewhat confusing and we learned that the new leakdown tester hose would sometimes leak around one of the crimped on hose ends but if turned just right we could not hear it leaking.

Here are the results from those 2 tests. We had warmed the engine up and pulled the spark plugs but by the time we got to the bac cylinders by the firewall, the engine was much cooler..
Test was done starting at the front cylinders 1,3,5 and then the rear 2,4,6
Cylinder 1 - compression = 164 - - - leakdown = 55%
Cylinder 3 - compression = 182 - - - leakdown = 11%
Cylinder 5 - compression = 180 - - - leakdown = 15%
Cylinder 2 - compression = 190 - - - leakdown = 22%
Cylinder 4 - compression = 195 - - - leakdown = 5%
Cylinder 6 - compression = 195 - - - leakdown = 4%


The next day we removed the serpentine belt, coil pack, radiator hoses, thermostat hosing, and several other parts to clear working space and repeated the compression test. This time with the engine cold (couldn't start it because some of the plug wire connectors had come off while removing the wires on the rear cylinder.)
We tested it cold and dry and then added some oil to each cylinder and repeated the compression test.
Oddly with the engine cold, cylinder 1 compression had gone up compared to the previous day with the engine warm. We had also replaced the O-ring on the adapter and used a ratchet and socket to snug the adapter in a bit more then we cold by hand.

Cylinder 1 - dry compression = 180 - - - wet compression = 210
Cylinder 3 - dry compression = 182 - - - wet compression = 210
Cylinder 5 - dry compression = 182 - - - wet compression = 200
Cylinder 2 - dry compression = 191 - - - wet compression = 205
Cylinder 4 - dry compression = 192 - - - wet compression = 210
Cylinder 6 - dry compression = 195 - - - wet compression = 205

Since we had to return the leakdown tester with the defective hose. We removed the schrader valve from the compression tester hose, set the air compressor regulator to 100 psi, and applied air to each cylinder with each cylinder on TDC. We listened for air from the exhaust pipe, throttle body, valve cover with fill cap removed, and oil dipstick tube and here are the results.


Cylinder 1 - moderate air from dipstick, valve cover, throttle body
Cylinder 3 - ok no air
Cylinder 5 - slight from dipstick, moderate from valve cover and throttle body
Cylinder 2 - slight from dipstick, moderate from valve cover and throttle body
Cylinder 4 - slight from dip stick, valve cover, and throttle body
Cylinder 6 - slight from dip stick, valve cover, and throttle body

Ok so sorry fro the long post but i wanted to get all the facts down from the testing we have done so far.
What other tests should we do and should we go a head and start dissembling the top of the engine to have a physical look at everything?

As mentioned when we did the first set of tests we started with cylinder 1 and the engine was warm. The next day it was cold.
After doing a wet test created a problem going back to re test the cylinders, particularly cylinder 1 that i wanted to re check. So we added gas to the cylinder and spun the engine over a few times in an attempt to wash the oil from the cylinder. we did that twice and let it set over night. Today I checked the compression on cylinder 1 and it was 180.

What are your thoughts?
could the brown in the coolant system be a stop leak? There is a new water pump on the engine that is not written down on the repair list.
Could the reason for the week #1 cylinder when the engine was warm be a crack that opened up when warm and sealed when the engine is cold?
Can gasses from the EGR in the plastic intake enter into the coolant if the seal is bad for the coolant to the throttle body?
Help
Thanks
Anna

I had similar issues in my cooling system. I suspect it is a result of improper maintenance. Coolant flush helped greatly.

The coolant leak is likely from the UIM. It'* not the failure that the series 2 is known for, but likely ends up with replacement most likely.

No telling if it'* stop leak or anything though.

I ended up pulling my thermostat and shoved the water hose in it, and started flushing until the water ran clear.

No telling on the rest, but I wonder how many other vehicles running fine return similar results.

If you go to fix the leak, I recommend planning for a full LIM gasket replacement teardown, and include valve cover gaskets too.

I would pull the heads and go through them and reinstall all with new head and intake gaskets.

I wouldn't pull the heads. LIM, probably. Heads? No.

If there'* an issue, I'm thinking it'* in the bottom end of cylinder 1.

I doubt it'* a big issue.

I suspect we may have thrown way too much science at it.

Lower intact is a must in this case. I like to rebuild the heads and install new exhaust studs and chase all the bolt holes. The lower end on these can run buku miles.

Thanks guys for the replies! Sure makes me wish it was my moms 77 Chevy truck... We got the upper intake off and ready to loosen the bolts and remove the lower intake..
WOW there are lots of electrical connectors!

I forgot to mention the engine has 128k on it.

We are trying to get the belt tensioner off but there is a pipe (believe its a coolant line) that comes out of the rear of the timing chain cover. it has a support bracket welded to it that fastens to the lower rear bolt on the belt tensioner. how does that pipe come out? it is loose and we can rotate it as far as the bracket will let us but it wont pull out of the timing cover.

No signs of water with the upper intake taken off. The port on lower intake manifold with the upper intake off, is much cleaner then any of the other ports.

Thanks
Anna

Oh, I just checked and the pipe comes out of the timing cover and connects to one of the heater hoses.

When I did it on the Park Avenue, I don't remember that pipe being welded to anything like you are describing. It was held in with a bolt and collar at the timing cover, and would pull straight out. Years of corrosion had worked wonders though, so it took sme convincing, but it was ultimately just the friction of a o-ring holding it in. It was also quite a pain going back in with a new o-ring

Haven't sized up the job on the Regal yet, but it'* possible the WBody had a mind of its own. Some of the plumbing does seem different

My 1997 PA also a 3.6 had a similar issue same symptoms with one port clean, it turned out to be the plastic intake plenum. Dealer said it was somewhat common if the engine had the slightest over heat. That happened at 136k, ran it to 245k sold it saw it around town for a long time after.