Coolant Problem

[andycrowther]

I have read through the problems with the cooling system and my car seems to be quite different.

Car.... Toyota Yaris 03 1.3ltr

Problem....  I drive on the motorway at about 50 or 60 mph no problem. I drive at 70mph and above when I come off the motorway the radiator fan is running constantly, when I get home the coolant expansion tank is full and it has obviously blown coolant out. I fill the system again getting rid of all the trapped air and it runs fine so long as I stay below 60mph.

What I have done... the engine coolant has been checked for hydrocarbon contamination, nothing. I have changed the radiator cap 3 times. I have changed the thermostat twice. There is a new water pump. There are no leeks anywhere. I have flushed the coolant system thoroughly 3 times.

Can anyone help?

[Notoyboy]

You certainly seem to have persevered with most of the possible offenders, particularly replacing the rad cap & thermostat for 2nd/3rd time.

How's the radiator? Any chance you have a partially blocked radiator?  Remove to flush/back flush?  Or radiator matrix blocked externally (eg. road muck, leaves, corrosion etc)?

Clutching at straws now, but in the past I have read that it's possible for a flexible brake line to collapse internally, with no outward sign.  Likewise, is it possible that one of the main hoses could have collapsed internally?

[andycrowther]

I could take the radiator hoses off, when I have taken off they seemed clear enough, I will have a good look today. The radiator works well, I tested by waiting till the thermostat was open then manually turning the fan on and monitoring the temperature using my phone engine app. The temperature drops OK. I also monitored the temperature when the fan cut in and that seems OK. Thanks for coming up with a fresh idea anyway.

[bathtub tom]

I'd flush the radiator with a hose in the engine compartment, thus pushing out any debris that could be blocking the air flow.

[andycrowther]

I have checked the hoses and they are OK. I have a cheap usb keyhole camera so I had a look in each cylinder, never used it before, only cost £10. Anyway cylinder 1 shows very small amount of contamination, the others where  spotless. So the head gasket has gone but only revs above 4000 ish. How odd is that, when its cold and running temperature its fine but when it gets hot the pressure is enough to blow the radiator cap.

[Notoyboy]

I'm no expert as to whether to trust the camera's view showing cylinder contamination, or to believe the lack of hydrocarbon contamination of the coolant means HG is OK.

As another long shot, I was going to ask if the car has a doubtful history, could someone messing have wired the fan to run the wrong way.

A temporary expedient would be to continue running at no more than 60 mph, with fan manually switched at/near this speed.  I'd guess the problem will only get worse, the more you use the car.  No knowledge of Yaris as to whether HG is an easy job, and how much.

Good luck.  Typical it happens in winter 

[bathtub tom]

I've experienced some very weird symptoms in the early stages of head gasket failure, but they soon develop into classic failure indication.