87 B2000 Overheat

Well finally got to work on the truck. Replace the thermostat and filled it up. Still no water in the coolant or vice versa.

It seems that the cap is leaking will need to replace that, but I am hearing a hissing sound from the exhaust side of the engine. I though I saw some dripping near one of the freeze plugs, but is seems to be coming from higher up.

Anyway it builds up pressure and is forcing the water out of the cap an into the overflow tank and then out on the ground. Pretty sure the water pump is working, but it is suspect. I can stop the fan clutch with the engine running at operating temp with my hand. Pretty much no resistance. Not sure if that is a good sign.

Truck runs great otherwise.

Allen

Question. Do the heater lines run under the exhaust manifold? I am wondering if one may be leaking.

Also is the water pump down be the lower hose? I may go ahead and replace it.

Still considering a diesel swap too.

I bought an 86 b2000 myself about 4 months ago and I had have the same problem. I put on an electrical fan to eliminate the stock and to help cool the motor, but had no luck. I replaced the thermo. and no luck there. There was no sign of water in the oil and I had good compression in all four valves showing that the gasket is safe. After running through a tank of gas to pinpoint the problem I blew a pin hole in the heater core hose coming out of the firewall. I have been reading and researching but these motors are famous for over heating. I am told to either go with an aftermarket radiator or get the stock one rodded and this should eliminate our problems. A lot of people remove the thermo. to make the truck run cooler, but in my instant for living in CA I will have problems smogging it. Hope this helps.

Did y ou find anything out?