My car has been running fine but yesterday the car began to overheat. It goes to 3/4 and stops. It won't get any hotter than that but I did notice it would go back to near normal temp at times. About 15k miles ago I did the timing belt, headgasket, water pump (with metal impleller), and changed out the oil cooler so I'm ruling those out for the moment. I pulled the thermostat and tested it in boiling water and it was opening. While the thermostat was out I felt the water pump impeller and it felt fine. I also ran some water through the radiator and it was going through. I put the t-stat in, bled the coolant and it's still overheating. I am getting heat so the heater core isn't clogged either. Any ideas?

BTW I also checked the coolant temp sensor and it was blue. I've read that the black ones are known to be faulty and are replaced with a green one. What about the blue one?

 

We need your car's details. I'm assuming it's a 1.8T because otherwise you'd have had to tear the engine down to get the t-stat out. I'm also assuming you checked the t-star recently, and that you had replaced it during the timing job. Have the radiator pressure-tested somewhere after you get the car to temperature and feel it. You may have a partial internal blockage, which you'll know if you find irregular heat in different areas of the face of the radiator. Also, it could be your fan clutch. Did you run the car and feel/hear the fan engage? It'll freewheel all the time, when it's not engaged, but you'll know it when the clutch engages. If its not, you likely need a new fan clutch.

 

Sorry, it's a 1.8t

I can't remember if I changed the t-stat when I did the timing belt. I checked it last night in boiling water and it did open. I got the car up to temp and it was overheating, I felt the radiator and it was hot near the top radiator hose and significantly cooler at the other end. The bottom radiator hose was cold.

Right now i'm leaning towards a radiator blockage which I wouldn't doubt because the oil cooler went bad and got oil in the coolant. I'll try changing the t-stat because it's cheap and easy. I'm kinda hesitant to buy a new radiator when i'm not sure thats the problem. I'm not sure what else it could be though

 

The radiator shop near me will pressure-check and clear out blockages for around $35. Well worth it, I think. You can probably find a similar deal near you as well.

 

Well I changed the t-stat and filled the radiator with CLR and let it sit overnight. Flushed the radiator this morning and the water seemed to flow through it freely. I'm stumped at this point, the only thing left at this point is the headgasket but I just changed the oil last week and saw no signs of coolant.

Btw both fans are working

 

It could be the HG and show no signs of mixing fluids - it depends on where the tear is. You'll only see it mix if the tear is between a coolant channel and an oil channel. If the tear is between a coolant channel and a cylinder, it's definitely going to overheat. The cylinder will be pumping hot combustion gases into the cooling system, overwhelming it (this happened on my wife's Civic a few years back). There is a test kit available that checks the coolant for combustion by-product gases like CO2, which will confirm or dispel that possibility. Well worth trying it before you rip the head off the engine.

 

A compression test should reveal this also, no?

 

That'll tell you a cylinder is leaking down somewhere, but it won't differentiate between HG, ring, or valve problems. It's a good first step though, and if you have low cylinders, at that point put a teaspoon of oil into the low ones, redo the test, and see what happens. If the numbers increase, it's a ring problem. If not, look into a leakdown test (checks valve sealing), and the HG test kit.

 

Well I think I rule out the headgasket. All cylinders were within 5% of 150psi.

The radiator is still only getting warm near the top hose so I think I will focus back on that.

 

I found the problem... Well I guess I should say the problem found me. On a test run the oil cooler coolant hose exploded. I replaced it and it runs at normal temps now. I'm guessing it had a small leak becase their didn't appear to be a loss of coolant or a visible leak when it first overheated. At least it wasn't something more serious.