First post here, I have a 98 ek with a d16y7. I replaced my thermostat because it was stuck closed. ever since, ive been slowly losing coolant. I dont have a blown headgasket, I have even compression across, and no milkyness in my oil. When i open my radiator cap when the engine is warm, i get a rush of air/coolant into my resovoir. Not sure if its air or coolant. Any ideas on whas happening? ive done a full bleed/burp aswell.

 

Aftermarket or oem thermostat?

 

Get the system full. With the engine cold, take the radiator cap off, start up engine and rev it. If bubbles continually come out of the radiator, there is likely a slow leak in the head gasket. This, and losing coolant with eventual overheating, are the only symptoms of a slow leak. You can confirm this with a block tester.

 

Thermostat is OEM Honda, And when i was bleeding it i checked for bubbles during high idle and reving and there were none, anychance it is my rad cap?

 

That is a possibility. You can rent a pressure tester and test both the system and the cap.

OEM thermostat should be good, some of the after market thermostats have problems with the rubber gasket fitting properly or other fitment issues, so that's why I asked.

The other place you can start losing coolant but not have much evidence is the heater core. If it has a pin hole leak, it will get worse, but initially the only sign is you can smell coolant inside the car. Usually when you kick the blower fan on with the heat.

The pressure test will tell you if the system has a leak as it won't hold pressure. Finding the leak can be quite the challenge.

 

I do smell coolant i the car, but only when i temporarily tirn the heat fan off. Its winter here in BC so i have heat 24/7. When heat is on i dont smell coolant

 

The system depends on a slight vacuum being able to draw coolant back from the tank to the radiator every time the car is parked as the engine cools off. If the seal in the top of the cap is bad or there is even a tiny air leak in the hose between the tank and the radiator, the coolant will move to the tank and not come back. The pressure tester does not test the top seal in the cap. Inspect it visually or just replace the cap.