Help please, I have a 1992 F250 with a 5.8L. A few days ago I replaced the thermostat becaused I noticed the temp. go from cold to almost hot in a few seconds ( truck had been running about 10 minutes, blowing cold air with heat on). In the morning I plan to drill a hole in the new stat to allow the air to pass through. What would be the cause of the vapor lock? (bad hose, radiator bad, crack in the block)?? Any and all help would be great. thanks Mike

 

Vapor lock is a fuel system concern, you probably have an air pocket due to an incomplete fill.

Try the small air bleeder hole at the top of the thermostat to see if you can get any remaining air expelled from the system.

Steve

 

I did drill a small hole in the thermostat today, it does seem to be working so far (the temp gauge was consistant [I drove around for an hour or so] and did not overflow any to the ground). I had the system full, I though, then I checked it tonight after the truck cooled down and added another half gallon. May this will be it, fingers are crossed.
Thanks for the help, Mike

 

I think the head gasket is blown, I took the truck to the shop today. Hopefully my #8 cyclinder is not AFU too.

 

Oil in the coolant? Coolant in the oil? Or maybe worse, can you see bubbling when you look into the coolant recovery tank? These are symptoms of bad HG. If not you may have just a sticking thermostat or coolant temp. sensor. Also does the rad. fan come on? Maybe bad fan motor or fan switch. You can check fan motor by turning on A/C (if you have A/C). Just some things to eliminate before pronouncing a bad HG.

 

When I had the radiator full there were still some bubbles when I had the cap off. (Had to add coolant every other day). The truck is in the shop right now I'll find out more tomorrow what's wrong.

 

I'm in the same boat, trying to figure out what's wrong on my 5.0L. Keep us posted.

Madmike33

 

well for both of you guys i woludnt pay much attention to the help you have gotten above.... geeessss... an electric fan on a 92 f 250 give me a break people read what the vehicle is at least..... a stopped up radiator causes your gauge to go up and down rapidly also causes internal boiling which will stop your heater. i would change the radiator not flush it ...mine wouldnt take to a flush and i had to take my heater hoses loose and force water through them backwards.... blows out any debris that has gotten stuck in your heater core.

 

I have a brand new 3" thick aluminum rad, what you said might apply to someone else and is good info, but I have a lower head bolt leak that leads me to beleive I may be drawing in air from there maybe causing an air lock, I also suspect the thermostat, either way I need to fix the leak, and the thermostat is cheap to replace. As for air flow, I live in Canada so these days, it's not any reason for overheating.

Madmike33

 

I do have a blown head gasket and I'm sill waiting to hear about the #8 cyclinder and the cost for it all.

 

Cracked head, cracked timing chain cover. Time for a new engine $$$$$$$$$$$$$$$$

 

Oh man, I feel your pain. Those big surpises are never fun.