3TJ Fan problems and overheating

[CMSMJ1]

Are you sure the rad cap has a good seal on the rad?

You are pissing in all directions without really eliminating one thing at a time.



the bottom line - if the bike is overheating and boiling it's coolant away - then turning the fan on all the time is masking the problem.

Your problem seems to be that the pressure in the system is low and as a result the fluid can boil at a lower temperature. << IS that about right?

So - your rad cap is fucked or not fitting right, or you have head gasket issues or a cracked block.

The fan is not the solution.

I'll go for a rad cap/rad interface issue.

[MarkT]

Thanks was a new cap, does the same with old cap, yes definitely lack of pressure so sounds as though I'm in trouble then to say the least!!

[CMSMJ1]

Absolutely sure it is not the top of the rad itself? I had a hybrid and it had a leak, biloing over etc - same as you describe. It was a badly fitting cap..sorted that out, little tweak on the alloy where it mountes and it was fine.

[MarkT]

I have wondered about that but visually it looks ok? But everyone's first thought it is rad cap!! That's why I bought a new one. If you watch the expansion tank when the engine starts it runs until the temp gauge gets nearly half way and the tank starts filling, following shortly after it starts boiling. You can quite easily pinch both the bottom and top hose together without much if any resistance.
Lack of pressure would explain low gauge reading? And the fan cuts in just too late, when the water is boiling but soon stops it boiling!

I have no real idea how to test the radiator seal all I have thought is to put a thinnish bead of silicon around the seal of the old cap and allow to set. Then try it with that cap? If it stops the boiling then I know what it is?

[CMSMJ1]

The expansion tank should not start to fill and certainly not boil til the motor is really hot.

If you take the cap off, fill it with water and run the bike - can you see the fluid rise and fall as you blip the throttle?

Sounds a touch like an air lock - so if you brim it, run it and then squeeze the hose - does the bike burp or does it have the coolant out the top of the rad?

Use water for this testing, it is a better actual coolant than coolant and is cheaper...

The bottom line is that either due to rad cap/seal issues or airlock you are not getting enough pressure in the system to prevent boiling.

[MarkT]

Yes it rises and falls, no burps. I agree about it should be very hot before it fills the expansion tank, and a radiator specialist recommended a racing cap that would be 1.6 bar compared to 1.1 as standard?

[Evilchicken0]

Well we know you have a 1WG in a 3TJ and no exup.

The engine overheats when you ride slow but not when you go faster. Maybe the engine makes more heat because it flows more mixture low down or the mixture might be a little weak, in which case you could look at it being undercooled ....
It might be the engine is higher in the frame than the 1WG again that might affect how much heat builds up.
If the surface area of the cooling pipes is larger then the pressure will be lower.
It could be a conbination of these which just pushes the numbers a bit to high.

Short term. If the fan cutting in at a lower temp means you don't boil the coolant then has to be good for the engine.
Medium term. Check the seating of the rad cap or fit the uprated one. Maybe get the mixture checked on a dyno which is easier now you can ride it there. You could vary the amount of anti freeze / water ratio, more antifreeze will push the boiling slightly higher (a 2:1 66% mix should raise the boiling point 10% against water only).

[CMSMJ1]

water pump might also be fecked.. might be missing blades and so the flow is not moving fast enough...too much heat soak...

[Evilchicken0]

I think he checked the water pump.

[Taggyd]

i asked if he had the correct rad for the engine aswell, if it's already the wrong engine for the frame, i'm thinking maybe if it is wrong it might be the cause of problems perhaps? assuming the pump is working fine, could opening the 'drain' screw on the pump housing help to check thatthe air is all out from lower down?