Hi all. Know this place is kinda a ghost town these days but figured I'd give it a shot.

Hello everyone. I drive an 05 Pontiac sunfire 2.2l automatic with ecotec. 250xxx miles, I've had it for about a year.

Recently my coolant level has been dropping over time, usually takes about 2-4 days and coolant overflow tank is empty or close to it. My engine has no radiator cap, it has a pressurized tank where you check/add coolant.

I have checked several times under the car while hot and running, and see no signs of any fluid coolant leaking anywhere. I see no white smoke from exhaust on startup, and I cranked the car with the coolant tank pressure cap off and there are no bubbles or pressure coming out the coolant tank, nor is there pressure buildup when I cover the tank opening with my palm.

However the car does have a weird misfire upon cold startup, it skips for about 3 or 4 seconds then smooths out to normal idle, and doesnt misfire again while driving. I did have a more severe misfire problem a few months back, but replacing the coil pack and spark plugs fixed that.

The engine temp has never been in the red zone since I've had the car, and the coolant temp always stays around 190 while driving. It did get to about 220-230F a few weeks ago one night when I forgot to check the coolant leaving work, but again never went in the red zone, and the next day when i left for work and refilled coolant it stayed at 190F as always.

I've just been topping off the coolant tank with 50 50 premixed antifreeze every few days, and continue to drive the car.

Now for my newest issue:

I had to let my mom borrow the car a few days ago to drive to work.

When she got home I checked the coolant level in the tank, it had not dropped much but I noticed oil residue floating on top of the coolant , as well as some milky buildup under the tank cap.

Tonight I rented a combustion leak tester from the parts store and tested the engine. I let it idle until it was at operating temp (190 F) and sucked the air from the coolant tank, making sure I didn't suck any coolant up in the process.

I'm not sure if it will let me post pics/video, but the test fluid stayed blue the entire 5 minutes I squeezed the test bulb, which indicated that there were no combustion gases in my coolant.

Now, I'm glad that I dont seem to have a blown head gasket, but I'm kinda stumped as to where the oil is coming from.

I dont believe my engine has any kind of stock oil cooler setup. It's just a cartridge oil filter housing that spins off to access the oil filter.

The only modification I have made recently is adding a simple inline transmission fluid cooler, the type with a tube and fins. No coolant interacts with the cooler in any way.

The only other things I can think of would be a crack inside the stock transmission fluid cooler on the inside of the radiator, or possibly a cracked head or block allowing oil to seep into the water jackets. Though I'm not sure how to test for any of this, especially on a tight budget?

Are there any other easy things to check that I am missing? Would it be a good idea to flush the cooling system and then check for oil buildup again in a few days to see if it was just a fluke?

Thanks for your help.

Get the uv dye kit to find the coolant leak.
Thermostat may be stuck closed. That would cause a leak and why the temp went up to 220°F. You need to fix before you ruin the engine.


"Are you sure your A/F ratio is correct? That hole in your Block custom?"

Buy a new resevoir cap


"Are you sure your A/F ratio is correct? That hole in your Block custom?"