I've been trying to figure out where my coolant is going and have hit a dead end. There are no wet spots under my truck at any point, nor can I find any wet spots under the hood. I've replaced the heater core, radiator, and ALL hoses in the past 2 years due to electrolysis but again, I cannot find any wet spots that would point to a leak. Also, truck fires and idles smooth, does not constantly steam out of the exhaust, and no strange smells or bubbles in coolant tank that would indicate its leaking into engine. This is on a 2002 4.6L Screw w/ 115k miles...


Any ideas? Any tests I can do to help figure out where it's going?

 

Coolant tank cap? Also, you can have a bad head gasket without smoke or poor running conditions. My Lexus had one for year before the oil finally got milky. The combustion chamber gas test goodie also did not indicate a head gasket failure.

Someone will correct me if I'm wrong, but Didn't the 4.6 get a plastic intake starting in 2000 or so and is subject to manifold gasket leaks?

 

Something else to note... No matter how hot the engine is, you can remove the coolant tank cap (also new) without risk of coolant overflowing. I've always thought that was weird but wasn't sure if it was indicative of any problems. I thought since there wasn't a lot of pressure trying to escape when the cap was removed meant it (the pressure / fluid) was leaking elsewhere.

 

When my engine is hot, if I take that cap off, I'm a burn victim.

What part of the country are you in? Where does the temp gauge ride?

 

I'm in the southeast and my temp gauge stays right where it always has, about a third of the way up... Not sure how else to describe it. I could drive for an hour, pull over, pop the hood, and immediately unscrew the cap with no concern and not even a real loud hiss. It's done this as long as I can remember and I've had the truck since mid '04.

 

You probably need a new cap. It should be holding 15 psi.

 

You can perform a hydrocarbon test on the coolant to check for a failed head gasket... but check the cheapest things first.

 

Like glc said, replace the radiator cap. That's the most obvious reason for not holding pressure. After you do, and have refilled the cooling system to the normal cold level, squeeze the upper radiator hose with the engine hot. You should find it will not squeeze, which means the system is now holding pressure. DO NOT unscrew the cap if it's holding pressure!

If the hose is still soft, you have a pressure (and fluid) leak somewhere else.

Have you looked very carefully along the seams of the radiator for signs of a leak? You may not see any wet spots, but if coolant is seeping out, it will leave a colored deposit on the radiator surface. If this is the case, I'd replace the radiator rather than trying to fix it.

Hope you find it.

- Jack

 

I highly doubt the cap is too blame, this is the 3rd cap I've put on it. I've inspected everything (rad, hoses, etc) as best I can and cannot find anything. I'm assuming it's leaking into the engine at some point and will eventually become a nightmare for me. This is my primary vehicle and I was really hoping to get more miles out of before encountering any major repairs.

I've also got a '99 Expo (dad's old truck) that def has a cracked head gasket. As soon as you crank it, the coolant tank is bubbling and it smells of pure exhaust. Funny thing is, it fires just fine, idles smooth, and drives without any probs. It rides/shifts extremely well and I would hate to get rid of it b/c of the head gasket. I know eventually it will become a much bigger problem but I've never attempted a repair job that big and no way I'm paying someone to do it.

Based on the info I have at this point, it looks like the expo has a cracked head gasket and the f150 might have an manifold gasket issue.

Have any other weekend mechanics on here ever attempted repairs such as this? Tips?

 

I would go get a hydrocarbon test done on the coolant. O'Reilly's should have a kit.