I am pretty familiar with components of cooling systems and so forth and I haved searched but this seems to be a strange problem. I am working on my friends sc300 and am trying to help him figure out what's going on with his car causing it to lose coolant and overheat.

Its losing coolant and overheating. I drove the car today and it didn't overheat at all. But I can get the temp needle to go up close to the Hot mark. I managed to do this by reving the engine at 3000 rpms for about 2-3 minutes and the temp needle was rising slowly but surely up to the "hot" line.

He has already replaced the radiator (due to a leak), replaced the thermostat, had the coolant flushed, and the radiator cap has been replaced. The only thing left to be done is the water pump. The car is not leaking coolant from what I can tell. There are no puddles of coolant under the car, the car's coolant is full when it is overheating. The fan is working properly... There is no milky substance on the oil cap, no bubbles on the dipstick. No abnormal noises coming from the water pump.

I am out of ideas. I did a compression check and all the cylinders were within spec. and were all about the same. I though if a water pump was bad it would make a noise and or it would leak coolant.

The one thing I did notice is that when it was hot in traffic I let it cool down a little bit at a red light. (Turned off the engine and the temp needle went from 3/4 from the H mark back down to the half-way mark within a matter of less than two minutes.

Also, about five minutes later I got to his house and popped the hood and you could hear a hissing noise coming from the radiator style cap. Anyone have any suggestions? I'm thinking the water pump, but that doesn't explain the coolant loss unless its evaporating. I did smell coolant, but I didn't see any steam coming from anywhere. Sorry about the long post I was trying to be very descriptive.

I should also add, his car has very little heat coming out of the vents. Mainly just cold air.

 

have u tried burping the system?

 

i had a similar issue when i did the timing belt, water pump, thermostat, and front seals last year. there is a certain way to put in the thermostat. the little weep hole on the thermostat has to go in at 1 o'clock position. if its installed any other way the car will over heat after about 5 minutes of driving. the only thick that i noticed is that when you face the thermostat to the 1 o'clock position and install it, it will shift over to the 3 o'clock position and still over heat. i positioned the thermostat to the 11 o'clock position and put it in. i did it in november and til now, about 10k and several drift events later no problems.

good luck with that. i hope this helped in some way.

 

radiator cap, if it's hissing it's bad. A water pump usually makes a sound/leak coolant. Look at the engine from underneath, it'll usually tell you if it's leaking coolant.

If the thermostat is bad, then it would be stuck closed, and if that's the case, the car wouldn't be losing coolant. But I would replace it anyway just to be safe.

 

Turn the car on and take your radiator cap off and see if you can see bubbles. You could have a blown headgasket. Make sure the fan is working, the clutch could be bad causing it to heat up.

 

All very good info. Thanks. So the radiator cap shouldn't hiss at all? Even if the engine was in between the half mark and the Hot mark. Its like a pssssssss....................... sound. I will check/replace his thermostat to make sure its installed correctly. I'll also double check to make sure there's no air in his system.

 

Sounds like you have bubbles in the system. Turn the heater to high while the cars on and check the coolant level. Add more if necessary. As mentioned, the radiator cap should not be hissing. If the caps bad, def get that replaced.

 

heater core?.. do u smell sweet coolant smell inside the car?.. Check up under the dash on the passenger side for wet spots.

 

i had the same issue w/ my nissan. compression showed that it was fine, oil not milky, etc., but it was indeed a blown headgasket.