We recently brought my 1978 F150 351M back to life after sitting for 15ish years. All was well until we saw a little white smoke coming from somewhere around the driver side valve cover. We immediately turned the truck off and assumed the water pump or thermostat was bad. I changed the thermostat, and we worked on flushing the block. We took off the fan and pulley from the water pump and spun it by hand to see if it was working, and it is. But we’re still having the same issue. Any ideas?

 

Are you actually overheating where the engine is boiling over, showing HOT or are you just seeing this steam from the valve cover area? What area on the valve cover, front, middle or towards the firewall?

 

I haven’t ran it long enough to see it boil or get the temp gauge up to hot. The steam seems to be coming towards the back of the valve cover/firewall. It’s also pumping white smoke from the exhaust, if that helps the diagnosis.

 

If the exhaust doesn't have a sweet smell to it, it's doubtful that it is coolant but worth checking. At this point, I would either borrow from the parts store a pump to pressurize your cooling system or have someone do it and see if the cooling system holds pressure. I do not recall anything at the rear of the engine which could leak other than a freeze plug or head gasket begining to leak which could help explain the white smoke out the exhaust..

 

sounds good! I appreciate it! I’ll update soon.

 

One of those telescoping little mirrors might help you to identify the hard to see spot.