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Truck was running too hot last week. Not overheating just running to the high end of the normal range. Went to add coolant and added over 1.5 gallons of coolant and water.
Took the truck out and ran it for about 30 minutes and it ran in the lower half of the normal range. Went out the next morning and there was a substantial puddle of coolant under the truck. Not all that I added, but a fair amount. I figured I overfilled it and went on. Drove the truck to work Sunday and Monday and ran cool. This morning when I got to work I notice the smell of coolant and more was dripping out just behind the front suspension left a decent puddle. Truck is running warmer on the way home.
Look at water pump while idling and pressure is normal in cooling system - watch for weep hole behind pulley for water pump; may only leak after it runs a few minutes. Make sure there is enough water coolant in the system after the thermostat opens - temp gauge up to normal. Also look at seams on side tanks of radiator - they will leak after a few years especially on cold mornings. Sometimes they can be repaired by recrmping the tabs that hole them on to the core. Good luck!
The tanks on the ends of the radiator are plastic in most cases. At least they were on my '90 302. Had a hairline crack in one of them and it only leaked after it got hot and then it pee'd out into the engine compartment. I don't know if some of the parts places,i.e. Autozone, loan a cooling system pressure tester, but it might be worth checking. Might want to clean your engine pretty well, run it so it would leak and inspect to see if you can tell where it is coming from.
I haven't seen this talked about much. You can go to NAPA and buy a little bottle of UV dye to put in the coolant. Then, with tiny leaks you can't find, the dye will leak out and mark where it's leaking. Then you just get one of those little ultraviolet penlights (leak detection) from the air conditioning section of Autozone or whereever and go looking when it's dark. The tiniest leaks show up this way.
Well, it comes in a little bottle with maybe an ounce in it, and it's specifically labeled for coolant. It's about $3 at Napa, and at my Napa it's behind the counter, you have to ask for it. I would assume other places would have it too..
I've never used dye for A/C that wasn't mixed in with a regular can of freon already, so I'm not sure how else that's available.
The moment it hits the coolant it turns this bright glowing green that looks like something Homer would be handling in the nuclear plant on "The Simpsons". Real easy to see when it leaks out.
When you say overflow tube, do you mean into the plastic bottle? Could very well be the cap. Maybe it's not holding to the pressure it should. Would be a very inexpensive place to start.
Yeah, try the cap, it shouldn't be coming out of the cap. I had a similar problem, I had to put a small hose clamp on the overflow tube, it's supposed to go into the tank if the cap releases it, not on the ground. Try some of that dye too, you'd be surprised where else you'll find leaks.
My 86 six did that at the start of Summer. About a week later the water pump went bad. Week after that the head gasket went. Week after that the motor went. Hope you have better luck. Got it sitting out back now with a "For Sale" sign. Went and got me a 89 with the 302. Hope it lasts longer.