Q: White goo/gunk under radiator cap

asked by on

A/C wasn't working this summer. Changed thermostat. Air working. Recently flushed radiator, and noticed a white gooey substance on cap and in fluid. Car does not overheat, and cabin heat working fine. No signs of leaking externally. Also changed radiator cap. Not sure what to do with this.

My car has 104000 miles.
My car has an automatic transmission.

Hi, thanks for writing in. I’d be happy to provide my insight.

This is often times a sign of a blown head gasket, however if this were the case your car would be overheating. I would recommend checking the oil in your car to see if it looks milky or has a white color to it or any signs of water. Also, check the coolant to be sure you do not see any signs of oil in it. If either of these are true, you may have a blown head gasket.

If you would like help, consider having an expert automotive technician from YourMechanic come to your home or office to inspect this substance for you, and make or suggest any repairs as needed.

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
  1. Home
  2. Questions
  3. White goo/gunk under radiator cap

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

Q: Can I add water or fluid to the reservoir till I can get a flush and fill?

Yes, you can, and should, add coolant to the reservoir to make sure the engine cooling system does not run low. Add only a 50-50 (water-antifreeze ratio) coolant mix to the overflow tank, particularly if it is winter season. If...

Q: I have a mazda 3 2007 and I do not know where the TCM is. It is not under the battery, so where else can be?

The transmission control module (TMC) is located directly on top of the transmission under the battery tray. If you need further assistance with replacing the TMC, then seek out a professional, such as one from Your Mechanic, to help you....

Q: Belt hanging down

It needs to be determined which belt has been thrown, or has broken. One belt drives the alternator, and the other drives the AC compressor. A thrown belt is generally caused by a seized peripheral - such as an alternator...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...