Ok guys, this coolant is magicly disappearing on me. I flush it, put in new stuff, get all air bubbles out, drove 3 miles, let it sit for a few hours, and the reservoir dropped a good inch and a half. Have checked all hardlines, gaskets, radiator, etc. No drips. I'm not blowing white smoke and I assume if it was coming out the tail pipe that fast it would be thick white. It's disappearing just sitting in my yard. PLEASE HELP! SOC, save our coolant

 

Did you change the rad cap? Also its common for the reservoir level to go up and down as the truck heats up and cools down.

 

Have you checked your oil level??

 

The coolant in the reservoir and radiator is dropping, significantly just sitting there. I haven't changed the cap. Just got the truck about a month ago.

 

Yeah, my pan has a miniscule leak, but the oil levels are fine. Drove it three miles back from the shop after having a gasket replaced. Let it sit and now it's way down. No drops anywhere.

 

Ok so the rad level is also dropping. My guess is that you have a pinhole leak somewhere. They are hard to spot unless you pressurize the system .

 

That's what I thought. But it's dropping a lot just sitting over night. I'll check for pinholes though. There's good pressure running through the system. Maybe it's getting into the overflow somehow?

 

I also have a '96 150XLT with 302cid engine (reg cab long bed, Manufacture Date 11/95).
I also experienced the same mysterious loss of coolant. Replaced the rad cap, etc. Still losing coolant. Last resort, added half bottle of Wynn's Stop Leak to radiator. Drove truck a couple of days.....result: problem solved....No loss of coolant in past 2 months!

 

Believe I finally solved it. Flushed the whole system out, tightened hose clamps, repaired gaskets. Put it up at an incline and added new fluid, let the truck idle through a full quarter tank of gas, burped out all the air. I think there were just some massive air pockets in there from before. Thanks for the advice everyone.

 

I have the same problem. Does anyone know if Bars stop leak is any good?

Thanks Rick