Hi I thought it could be the headgasket. I own a 150 honda carb model. the haed was milled and a reprifield cam was added , and a weber 36DCD carb with couls air intake was also added. it started a while agao to run warm when doing WOT on the high way. But now it ocours more often. When driving in town the heat seems fine and it doesnt overheat, but as soon as yoy reach the highway and go all out it tends to overheat, but by putting on the heater the temp seems to drob. had a look in the overflow bottle and it was full and overflowing and rad, needed topping up, so every one suggested, that the headgasket was shot. Well i emptied the overflow bottle and went for a drive, bottle didnt filled up or over flowed, didnt top up the radiator. When i topped it up the rad, the bottle was again filled over its max. level after a hard drive. Could it be a blocked rad or is it the head gasket? termostate was replaced and the cap and all hoses.

Goint ot to a pressure test today
Need help please

 

it is most likely the head gasket. The compression from 1 or more of the cylinders are leaking due to a bad head gasket. The air then is forcing the coolant to go where ever the easiest escape is, which would be to the reserve and then out of the reserve.
The easiest way to check this is:
1. Fill up your radiator leave the cap off.
2. Start the car, and use the throttle body to rev the car a little don't rev it real hard or you'll blow coolant all over the place. Just keep a higher then idle rev
3. Look to see if the coolant is bubbling in the radiator.

This could be caused by both a cracked block and a bad head gasket. It is more likely that its a bad head gasket.

The exactly same thing as you explained has happened to me twice.

 

Hi, thanks for aal the info. It seems as it wasn't the head gasket but the radiator. Took it out over the weekend and took it for a good clean-up. There was a lot of dirt in it. Put it back yesterday, bleed the system and went for a drive, no overheating, then in town after stop and start driving for a while it suddenly overheated, stopped, and let it cool and topped it up again. This morning took it out and it didn't over heat. So I guess it was a bloked radiator.

Now I need some info. Is there a way to wire the Radiator tempswitch so it good let the fan run on for awhile after shutting the engine off?

Thanks again for all the info.

 

you could just wire the fan to run all the time (when the engine is on). Make sure your system is bleed completely. Run it again til its real hot or over heating, and crack open the bleeder screw, see if air comes out, if there is air keep topping off your radiator and bleeding. - just a suggestion

 

Thanks for the info doublejz, did wire the fan to stay on while the engine is on / ignition, with a switch , but would like to know how to if the ignition is off. About the bleed. Should I take the radiator cap of while i am opening the bleed screw when the engine is hot, and top it up or must i let it cool down and then top it up.

I bleed it and closed the screw, started the engine and let it run, and topped it up while it was getting warm, the fan came on twice, i topped it up again and closed the radiator, and shut it down...is that the wright way or is there another way.

Thanks

 

get a new radiator cap. The problem you describe is EXACTLY the same as mine. A new cap and you will be in heaven.