My 95 150 with 351 AT has a random loss of coolant. A little history first. This truck was owned by a friend of mine. He purchased it in 1999. I purchased it from him about two months ago. From day one when he bought it in 1999 it would loose coolant. No sign of leaks or any sign of it going into the oil. It is very random. You may drive it for a couple of weeks and it never loose a drop. Then one day open the hood and it will be low. I have been checking it about every other day and it does not go down a little every time I check, just all at once it will be about a quart low. Really strange. And as I said no sign of leaks. What do all of you think? Thanks in advance.

 

My 1994 truck did that too!

I was always curious on that...

No cracks in the resevoir, the line, NEW radiator, hoses, T-Stat, T-Stat gasket.....Seriously...Never figured it out...

 

I had similar symptoms and determined: a.) blown out thermostat housing gasket. Was on the back-side of the the hidden mounting bolt and would pass fluid into wells in the casting behind it. b.) Weep hole on bottom of water pump was dripping a bit. As we all know, when the bearing is going out, it starts to weep. Mine weeped just enough to run down the lower hose or just enough to leave a green glob on the crank pulley.

I'll still smell coolant every once and a while and I check out all the "usual suspects" big time now.

Good luck!

 

I changed all hoses and the thermostat when I got it. CHecked the bottom on the pump. No dripping there. May do as sidewinder and just add to it when needed and dont worry about it.

 

Only other plausible option is a cracked head.....But then, it'd have other issues...

 

Mine losses a bit then seems to quit. I believe mine leaks from the pressed in fittings on the water pump. Never been enough to overheat it though.

 

Could be a head gasket. Have you done a compression test on it? After checking everything you have, that's probably where I'd go next.

 

When found to be missing what is the reservoir level at? if radiator is low the reservoir should be empty, if not, inspect the overflow hose for cracks, or loose connection... When you refill, and when cold, are both the radiator and reservoir at their cold full level's?, (the reservoir has a cold mark, I'm sure that you already know that)

 

Slip, I always check it cold. I try to keep the reservoir at the cold mark. For whatever reason some days I will check it and it will be darn near empty. It was full yesterday and I checked it this afternoon after it sat for 7 hours(so it is cold again) it was still full. This was after a 2 hour 125 mile drive this am. You would think it would leak in that much driving. Maybe I need to replace the overflow hose? That would be the only one I have not changed.
As for the head gasket I have and the truck has never had any other issues with the engine. If it was a head cracked or a gasket would it not lose consistantly? And after all these years of it doing this would there not be other problems by now?

Slip I think I will put that overflow hose on and see what it does then. If it still looses coolant I will get a compression check done.