traces of oil in coolant

[RichardS]

Hey everybody,
Yesterday I picked up a 2003 Buick Century. It was a snowbird car, with maintenance done religiously by the dealership. It's at a lowly 104k miles, so I already have a list of to-dos, but noticed about 1/4 teaspoon of what oily residue on the radiator cap.

This engine is known for it's upper intake manifold leaks, but that always gives you coolant in the oil, of which I can not see any. The oil isn't milky, and through the fill hole, the engine is extremely clean. I'm sort of hoping that it's just gunk from 13 year old dexcool, and have a radiator flush as the first thing on my list.

Assuming it is oil, any ideas? I was thinking it might be a leak in the radiator itself. As far as I can tell, both the transmission and oil run through there for cooling.

Thank you.

 

[Robenstein]

Might very well be old dexcool slime. I have also known some real lazy mechanics that use one drain pan for everything....oil, coolant, atf, ect. And I have seen those same lazy mechanics dump oil contaminated coolant (after a hose change) back into the rad.

Maybe something like that happened if is not dexcool sludge.

 

[The_German]

I think Rob is correct. If it isn't the reason I'd be surprised if you don't see chocolate milk in the crankcase when you change your oil...

Also old Dexcool is a LOUSY product.

For fun I'd run a UV dye in the engine oil to see if it migrates by the end of the OCI into the Rad.

Oil might get pushed through a HG leak under heavy load and the PSI of the Rad might be the low (receiving side) of the leak but that is a bit of a reach.

Re-using old coolant from a dirty oil change pan is such common practice... How else do you think those pans get cleaned (lol)?

 

[fonecord2]

I wonder if it's harmful to the cooling system?

 

[69GTX]

Originally Posted By: The_German

Also old Dexcool is a LOUSY product.


ANY old coolant beyond its useful life is a lousy product.

Nothing wrong with DEXCOOl other than lazy people who don't keep an eye on their cooling systems. Dexcool beyond 5 yrs is asking for it. My Camaro had 13 yr old factory DexCool in it when I bought it. The inside of the system was perfect even if the coolant was a nasty brown color. Dexcool doesn't mix nice with some other coolants and can cause sludge. It also doesn't like air being introduced into a less than full coolant system. Otherwise it's a great coolant. If you plan to switch coolants, ensure you get every bit of old DexCool out of the system. It might just be easier to stick with DexCool. It's a fine product that the 3.8L V6 gasket witch hunters don't care to understand...an issue resolved years ago.

Old DexCool sludge is a brown/dark orange color. If the stuff under cap is a whitish, waxy substance, that's probably not DexCool sludge. Consider other sources of oil contamination into your coolant from PS/transmission coolers, if your is so equipped. Those will usually give you reddish floaters if leaking into the coolant.

 

[Donald]

I think someone used a contaminated funnel or drain pan.

Obviously keep an eye on it.

I had a 1980 or so diesel VW Rabbit with a bracket block. I changed the water in the cooling system weekly to deal with the oil. Traded it to a dealer.

 

[Lubener]

Old Dexcool. Seen it many times when car shopping. Needs flush and refill again with fresh Dexcool. BTW- nothing wrong with Dexcool if the cooling system is maintained.

 

[The_Eric]

Originally Posted By: Lubener
Old Dexcool. Seen it many times when car shopping. Needs flush and refill again with fresh Dexcool. BTW- nothing wrong with Dexcool if the cooling system is maintained.


Yep. It's an excellent product in a properly maintained system.

The trick is to make sure ALL the air is bled out and to use a new OEM radiator cap, then overfill the overflow tank by several inches to assist refilling when the engine cools back down.

 

[RichardS]

I've already drained all of the coolant out, and replaced with a flush and distilled water.

The power steering fluid is black, so I'm thinking it's not that. There are transmission lines into the radiator, but the fluid in the trans is a lovely pink and properly filled.

The only low fluid is the engine oil, but the pan is covered in oil, so it could just be a leak from there. I'll snap a photo of the radiator cap, and hopefully that will make it easier for everyone.

Any suggestions on a favorite UV dye? It's due an oil change, so I can just dump it in when I do that.

 

[RichardS]

I had previously wiped a majority of it away, however that's the goop that was on the radiator cap, and to a small extent, in the overflow.

What are the chances that the a/c system sprung a leak in the radiator, and that's just the lubricating oil from that? As of now, the A/C is the only system that's non-functioning.

 

[Virtuoso]

A/C systems aren't tied into the radiator... but the auto transmission usually has a cooler in the end-tanks.

Chances are that's just old coolant. Change it out, run a UOA and keep and eye on it. Oil in the coolant is real bad for the hoses. It breaks them down and eventually they will weaken and start weeping all over. I had an SOHC 1.9L Saturn that had a head crack and load the cooling system with oil. Saturn's directions were to replace the head, all hoses and flush the system with Cascade dish detergent.

 

[RichardS]

Thanks everybody!

I'll update if the dye shows up anything funky.