77 overheating

[Arizona240z]

Got a guy at work with his 77 FI (looks fairly stock) overheating.... It's hitting the 250 mark in about 5-8 minutes (it's in the 90's today). Replaced the cap, put in some stop leak and still no better. What do yo guys think? It is holding pressure (I bumped the over flow bottle and the cap flew off. The water wasn't super hot, I was able to hold my hand in the water as it shot out.

Could it be a stuck thermostat? A little water was forcing itself out through the neck of the new cap. Hoping to get this solved ASAP.

[peterc]

Easy way to find out is to remove the thermostat and run the car without it. If it still heats up, try runing the car with the rad cap off (make sure the engine is cold before you remove the cap). If you don't see water flowing then the pump is worn and needs replacing. If the water is flowing then likely the rad is clogged, restricting the flow.

Hope this helps.

Cheers,

Peter

[JEFF]

A blown head gasket between a cylinder and the water jacket

will put HOT exhaust in to the cooling system. When that happens the thermostat gets 'steamed'. It will make the temp. guage skyrocket. Test the coolant temp. in the radiator with a cooking thermometer.

If you did put 'stop leak' in the radiator then I suggest replacing the thermostat anyway.

Why is there pressure in the overflow bottle???

- Jeff

[2ManyZs]

If it's pushing water over into the overflow bottle, I'd say it's either a blow head gasket or a bad radiator cap that is causing it to build up too much pressure in the radiator. If it's just a bad cap, it could be causing air pockets in the cooling system that is causing the pump to cavitate and cutting down the flow through the radiator.

Put a new cap on it and see if that helps any... if not.. then it's time to do some more testing.....While you are at it, flush the system with a good cooling system flush.. Stop Leak will only make the problem worse....

[Alan Pugh]

If it's a blown head gasket between one of the cylinders and the water jacket, it would have to be a fairly big leak to overheat the engine in 5 to 8 minutes and you would notice some rough idling.

Remove all the spark plugs and check for the one that is either showing rust or is very clean. This is always a good sign (not a good thing) that water is getting into one cylinder, which in turn means you are virtually pumping the water out of the engine by displacing it with air.

Another tell tale sign of this is to drain the block and radiator and collect the fluid in a bucket and check for rust granules. A bi-product of filling the cooling system with combustion gasses is rust. This rust circulating through the system then in turn reduces the impellor on the water pump to nothing but a flat disk.

For a car to overheat so quickly is quite strange and I would be interested to find out the final cure.

Alan.

[Arizona240z]

He had it towed into he shop so we'll see what was the issue.... I'll let you guys know.

Thanks