Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Pontiac 6cyl 3L build up of sludge in radiator

I keep having sludge build up in radiator and car runs hot. I know these vehicles have a known issue with intake gasket leaking so I;m aware of that symptom but here is the odd thing; The oil in crankcase seems fine, no milkyness, and I’ve drained and checked the transmission fluid which also seemed perfectly fine. So it seems that whatever is leaking into coolant fluid is not cross contaminating, and coolant isn’t getting into oil or tranny fluid. Is it possible that this still could be bad intake gasket? Or possibly the inner core of radiator where tranny fluid cycles through is leaking? If I have to say that any fluid levels go down more than the other it would have to be oil, but Ive driven the vehicle several thousand miles like this and just have to flush radiator system very regularly to stay on top of it

year, model, mileage?

I have one question: Do you use Dexcool in this vehicle? If you do then I think you have your answer.

Agree. You have to be super careful with Dexcool and change it out on time. Also have to make sure you have no leaks that can introduce air into the system. I’ve been lucky and mine has been fine but I was the reservoir to make sure the color is not changing on me. I think you’re going to need full scale flush and that may not do it.

That’s called Dexcool sludge.

Enter that into your search engine, and then click on images and you’ll see the scourge.


Yes…this is a real thing… What puzzles me is that nobody has the definitive answer as to what causes it. Some say it is mixing with other types of coolant…some say not…

The problem is real however…and probably why its nickname is DEX-KILL


It’s caused when air is able to enter the cooling system for some reason.

Dexcool is an Organic Acid Technology coolant or OAT.

This coolant turns acidic if it’s exposed to air which in turn eats up just about everything that’s involved in the cooling system.

I remember when Dexcool first came out.

Their advertisement statements claimed that Dexcool could last 5 years/150,000 miles.

They never said that Dexcool would last 5 years/150,000 miles.

There’s a big difference between could and would.


If I have to say that any fluid levels go down more than the other it would have to be oil...

Seems like oil is getting into the coolant, possibly through a head gasket breach or leak in the engine oil cooler (if you have one).

The OP states it’s a 3 liter Pontiac. Pontiac never used a 3 liter that I know of. Correct me if I’m wrong.

It’s a 3.1 liter.


@Tester That’s what I figured but if it actually is a 3 liter I wondered if it even WAS a Pontiac.

I don’t know?

When I walk up to my truck and it has Nissan badges all around it, I figure it must be a Nissan?


My neighbor had a succession of 3 large GM station wagons. The Chevy wagon had a 307 Olds engine, his Olds had a 301 Pontiac, and his Buick had a 305 Chevy engine .

Names and badging can get wonky sometimes. GM’s Geo line got confusing…it was Toyota under the hood. GM did play a lot of games with their engines and which department it came from for sure. Same goes for Chrysler when they got in bed with Mercedes. That Toyota Subaru collaboration is another confuser… One is badged Subaru one is Toyota but they both have nothing but Subaru under the hood… of course owners should know this.

This stuff is kinda getting commonplace…but those in the know…know who the mfg is in bed with…and they really dont keep this info super classified either. But yes confusion could arise…and rightfully so.

Most know what they have when they buy it tho…Then again…seeing some of the simplistic questions we see on this site suggests that what the owners know and or do not know is any ones guess


I have done extensive flushing of system every 3000 miles or so now- this is not average build up- trying to find out if it’s possible for oil or tranny fluid to get into the coolant system while both of those systems are not getting coolant cross contaminating back and forth- yes 3.1 liter

There is no oil Cooler FYI -only hoses going from radiator to tranny for cooling

And yes I’m using dexcool- though I have been contemplating using only water in order to determine which fluid is leaking in since the tranny fluid is also reddish coller and oil would just be grey gunk- I guess that might be the way to find out for sure which fluid is contaminating

There is no oil Cooler FYI -only hoses going from radiator to tranny for cooling

The radiator does have an internal oil cooler for the trans…so yes you can get trans fluid in your anti freeze. Not that common…but sure it could happen…it flows through the coolant inside a copper or aluminum tube to cool itself

You sure this isnt the Dex-Kill sludge that occurs when it contacts air as previously discussed? Oil is pretty easy to spot.


If your dexcool is clouding up in three weeks, you need a new radiator cap. If you have a bad intake manifold gasket, the coolant will leak into the manifold, then get into the combustion chamber where it burns and exits the engine as steam. It won’t necessarily contaminate any other fluids, but you would be loosing coolant at a measurable rate.