There is a small brown sludge oil layer in my coolant tan...

Q: There is a small brown sludge oil layer in my coolant tank.

asked by on November 17, 2017

I recently had my water pump changed. After a little while I noticed a thin brown sludge oily looking layer in my engine coolant reservoir. The bright red coolant is still in there and separated from the sludge layer.

My car has 100000 miles.
My car has an automatic transmission.

Often times, sludge in the radiator is an indicator of a leaking cylinder head gasket, which can lead to major engine damage if not checked out soon. A blown head gasket may cause a number of different symptoms. A head gasket that fails between cylinders will generally cause a misfire and potentially compression leaks from one cylinder into another. Low compression will eventually result in a rough idling engine. When the head gasket fails between a cylinder and the coolant port, coolant may leak into the cylinder causing it to be burnt with the fuel charge in the combustion chamber. This often results in misfires on startup, especially after the engine is run, turned off and restarted and in some cases may result in the engine not maintaining enough cylinder compression to even run or start. You may also notice a slight bit of steam like smoke being produced from the exhaust as a result of the coolant being burnt inside the combustion chamber along with the fuel charge. This type of failure may not always show with a compression test. I would recommend having an expert from YourMechanic come to your location to properly diagnose the symptoms you describe.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Audi Q5 gets short of coolant in the reservoir and when I turn on my air conditioning it seems to drain 2012 Audi A5 Quattro

Hi there, unless the "coolant loss" you continue to see is the result of an incomplete coolant bleeding procedure, there is still a coolant loss somewhere is the cooling system. Hopefully, the "temperature rise" you mention did not cause overheating...

How do I use the engine block heater in a 2012 Nissan Altima?

If your car is equipped with an engine block heater, this is an important safeguard to use during severe cold weather. Here’s how to use it (if your car is equipped with one): Make sure the engine is off....

How safe is it to drive with a torn caliper boot?

Hello, thanks for writing in to YourMechanic. If the caliper boot is torn open then you will get dirt, debris, water, and road salts in the caliper piston surface. The caliper may seize or tear the caliper piston seal causing...

Related articles

A Buyer’s Guide to the 2012 BMW 7-Series
When When power, performance and luxury are at the top of your list, the 2012 BMW 7-Series is sure to be a perfect fit. From the stylish design to two length options for enhanced comfort, three available engines and two...
A Buyer’s Guide to the 2012 BMW ActiveHybrid 7
The The only thing better than a hybrid car is one that is designed with luxury and performance in mind. The 2012 BMW ActiveHybrid 7 nails it in all of these areas, and considering that it clocks in with a...
A Buyer’s Guide to the 2012 Subaru Forester
People People love SUVs, but more and more people have been looking for an alternative to the large models that suck up a lot of gas. One of the best options to consider is the Subaru Forester; it’s a great...