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'06 Mountaineer Hissing sound/leaking coolant

I recently got my oil changed & the auto body shop told me that my coolant is leaking and that I needed to fix it ($800) I took my car to private mechanic & he said I was simply missing a cap, replaced it ($25) & that the issue would be resolved. After driving it for a few weeks I can tell there is still a problem, I hear a hissing noise, on the passenger side that appears only while accelerating & after I turn the car off (for about 5 seconds). Also, after I turn off the heat I hear a loud gush of air for a few seconds. The car is slower to accelerate these days. I am strapped for $ and DON’T want to take it to an auto body shop (too pricey). Is this a potentially serious problem? Should I get it fixed immediately? How expensive are we talkin’ here? I am a female who is not car savvy & neither is my boyfriend! Thanks!

You need the cooling system pressure tested to locate the leak and have it fixed. The test is easy for a good shop to perform. Auto body shops are not recommended to do this. There are special Cooling System shops that will tell you within 10 minutes where the leak is and what should be done about it. No need to go to the dealer for this.

Thank you!

The noises suggests there is air trapped in the cooling system. It is hard to get all the air out of the cooling systems of some vehicles. Also, if you have a small leak in the system, it is possible that air will be sucked into the system when the engine cools off.

You need to have the system pressure test to verify that it is not leaking.

Make sure the coolant reservoir (aka “degas bottle”) is filled properly (this is the translucent plastic bottle with the “radiator cap.” Refer to your owners manual to make sure you know which one it is and the proper type of fluid to add. If the bottle is not properly filled, it can let air into the system when the fluid cools down.

If you don’t have an owners manual, you can download a copy from:


thank you!

Look in the yellow pages under “Radiator Shops”. Or “Radiator Repair”. Those places have the experts to diagnose this kind of problem. Although most any inde shop should be able to also. You might ask your normal mechanic for a recommendation of the best local radiator shop.

In the meantime, be sure to keep your eye on the coolant level frequently, and when driving, keep an eye on the engine temperature or any indication on the dashboard that the engine is overheating. If it does, the first thing to do is turn on the heater to max and the heater fan to max. It may make it too hot inside, so open the windows if necessary. This will remove some heat from the engine temporarily, but if it persists you’ll need to pull over and have the car towed. Overheating can cause very expensive repairs.

Thank you!!!