: 1998 STS engine full of mystery sludge?!

07-17-09, 12:41 PM
I have a customer with a 98 STS. The vehicle has 116,000 on it however the engine was replaced at 70k with a brand new, straight from GM unit. He has his oil changes done with us and we always use 7.5 quarts of Mobil 1 Full Synthetic 10W30 per his request/vehicle specification. The car doesn't get driven very much and he brings it in once a year, which equates to 5k miles to get the oil changed.

Yesterday I recieved a call from him saying "My car is at the Cadillac dealer, they say you put the wrong oil in it which caused it to over heat and it cooked the head gaskets!"

I am familiar with these cars (I own a CTS-V and I am looking for a 2000-ish STS for a daily driver) I know that the Northstars eat oil and headgaskets as part of their normal diet. Even so, I went back to check his invoices and I spoke with the tech who worked on his car to verify that we didn't drop the ball somewhere along the line. Everything checked out. We changed his oil 5/08 at 110k and again at 6/09 at 115k. I am 100% positive that we put the correct quantity of the correct oil in the car when it was here. So that's good for us, but what about my customer?

This morning I headed to the Caddy dealer (same one that services my V, great guys there!) and took a look at the engine which is now torn down. The heads, timing chain, tensioners etc. were covered with a thick, black, gooey substance. It looks like black Vaseline. It is viscous(oily) but it doesn't smell like oil. Infact it has no smell at all. It also doesn't look like oil that has coolant in it. If you rub it between your fingers it will disperse and become more liquid but you can pick up "chunks" of it. It looks kind of like engine assembly lube, but there is TONS of it in the engine and the motor has 40k on it now, any assembly lube should have flushed through by now.

In talking with the customer, he said that a couple weeks after leaving our dealership he checked his oil and it was low a quart, so he topped it off with Mobil1 5W30 (he knows it had 10w30 in it, but he didn't have any handy) 600 miles later his low oil light came on again and he added another quart. There were no puddles or drips on the ground, which means the car was consuming a massive amount of oil!

I know we didn't put anything other than Mobil 1 in it. The customer swears he didn't use any oil additives, or "stop leak" type stuff. The Caddy guys haven't done anything engine related to the car for a while. So the question of what the hell the black goo IS and how it got into my customers engine remains a mystery.

Has anyone else run into this? Is it something to do with the head gasket issue? If the customer repairs his head gaskets, can he be confident that he won't have oil circulation issues down the road caused by this sludgey stuff?

It's in the Cadillac dealers hands now. We are sending an oil sample out for analasys to see if maybe we got a bad batch of Mobil oil or if something else was dumped in there by someone.

Sorry for the long read guys, I hope someone can shed some light on this! This guy is a great customer both here and at the Caddy store, so we all want to make sure he gets back on the road in his beloved STS soon!

07-17-09, 05:08 PM
Never heard of anything like that before. I'd be very leary of putting it back together without cleaning out every oil passage. I do hope that they Timesert every bolt hole before they put it back together or he may be back again.

07-17-09, 07:55 PM
I've heard of 10w-40 Dino oils turning to pudding when the additives wear out, but this is the first I've heard of it with 10w-30 synthetic. So it's very odd.

Synthetic is not that great for the flat tappet hydraulic lifters in the engine anyway. They lack the ZDDP needed to keep the friction down to keep the cam lobes from wearing and the lifters from cupping. There's a lot of stuff to read here on the forums about it. This is where I learned about it: http://www.cadillacforums.com/forums/northstar-performance-technical-discussion/156784-anyone-ever-do-headgasket-car-5.html

07-17-09, 08:06 PM
I've heard of 10w-40 Dino oils turning to pudding when the additives wear out
That was back in the 80's. I have experienced it, but it was not from additives wearing out. The car had 3K oil changes. I think todays oils are much better, but I still have too bad of a taste in my mouth to ever use a 10W40 again.

07-17-09, 09:44 PM
There are some engines known as "sludge monsters", such as the Chrysler 3.9 (I think it is) and some Toyotas, and a few other cars. Toyota has been replacing a bunch of motors so I'm told. The main culprit is a hyperactive PCV valve, which is just how those cars are made. Never heard of it happening on a N*, but it could be a faulty PCV valve just the same. Also with the low number of miles put on the car it's possible that the oil sludged up from not getting up to temperature but I rather doubt that would happen with Mobil 1. Any chance there is still some oil in the pan that you could send to a lab for a UOA?

07-17-09, 10:03 PM
Any chance there is still some oil in the pan that you could send to a lab for a UOA?
I think he said that the dealer is doing that.

07-17-09, 11:08 PM
The oil sample will come back showing excessive moisture and acids. Good chance the PCV system on the crate engine was never hooked up and/or the car is driven in a short-hop fashion and never allowed to warm up to operating temps.

07-17-09, 11:35 PM
Sounds like STP to me. I've seen engines where well meaning people try to treat an oil burner with a couple quarts of STP and the engine winds up looking like it's full of stringy sludge.

07-20-09, 07:49 AM
Wrong oil caused it to overheat? More like overheating caused it to cook the oil...

I never use Mobil 1 oil. Quaker State 10w30 and nothing else. Not to say it's better, I've just seen good results with it.

I would not re-assemble that engine without cleaning every part and washing out all the passages and galleries. I do hope they stud that engine... 3 GM dealerships have already stated they would never use an insert again after using the studs.