Hello,

Last year I replaced the radiator and flushed out the cooling system. At that time there was quite a bit of sludge in the reservior.

Over time, the sludge came back until it filled the reservior. Today, I took the car to a shop with a special cooling system flushing machine. The mechanic needed 2 passes on the machine to clean out the sludge. He thinks it was caused by engine oil but is not sure.

This sludge is black/green in color, odorless, oily, and has a pudding-like consistency.

If it is caused by engine oil, I would expect to see some coolant mixed with oil in the oil pan. But I don't. There is no funky milkshake stuff on the oil cap either. Nor do I see white clouds of steam out the exhaust when I start in the morning. Bad head gasket? Cracked head? Ouch!

Transmission fluid could mix with coolant through the heat exchanger. But I replaced the radiator last year. I used a schluko replacement so I can't rule this out.

Is there any way I can confirm the source of the sludge; engine oil or transmission fluid?

Are there any common problems with this car that would make all of this sludge?

Is this car on borrowed time?

Thank you,

JSP

 

what is the radiator made of? what kind of fluid additives are you using? I doubt it's engine oil from the symptoms. maybe some sort of wierd chemical/thermal reaction of the metal and additive or water that results in the buildup.

 

Hi Sliviaks2nr,
The radiator is plastic with an aluminum core. Looks just like the one I replaced.

I have been using Prestone ethylene glycol based green coolant as specified by Nissan. The radiator shop also used green coolant after the flush. Not sure about additive content though.

Forgot to mention that the car runs well in every respect. No overheating!

Cheers,
JSP

 

some coolants shouldn't be mixed or they will congeal, not sure that's your case if you've always used the green coolant.

i doubt it's oil even though it's oily, coolant is also a lubricant so that explains the oily part.

it actually sounds to me like it's pieces of your hoses that are rotting away. have you replaced them at any time or are they the ones that came with the engine off of the assembly line?

 

Its probably your automatic tranny fluid mixing with your coolant! there is a tranny cooling line that goes from your tranny to your radiator and back into your tranny, check your tranny fluid.

 

Timing chain assembly eating into the coolant line is the most common cause. Replace your front cover and timing chain assembly.

 

Thanks for all of the ideas. I did some more investigating this week.

Changed the oil - used 1/2 quart in 6000 miles over 6 months. The oil was dirty but contained no oil/coolant mixture sludge.

Removed rocker cover to replace leaky cover gasket. The inside of the cover was very clean!

Checked the transmission fluid level using the procedure in the factory manual. Level was at the top of the full marks and the fluid was clear.

All hoses major hoses were replaced last year. Some of the small heater hoses were not. Given the volume of sludge in the coolant reservior, I would be very surprised if the decay of a small coolant hose could be the cause.

I will keep an eye on the coolant and advise when I learn the cause.


Sincerely,
JSP