Where's my coolant going?

[Thor]

I have a 94 Chev 6.5 diesel with 300,000 miles on it. Have noticed that I'm losing about a 1/2 to 3/4 gallons of antifreeze every month or so. I borrowed a pressure tester, pumped it up and can't find a leak anywhere. I drove it on a 300 mile trip last week and started having a no heat/high temp reading on the temp gauge. Added another gallon of antifreeze when I got back and seemed to solve both problems, but still have coolant going somewhere. I did smell coolant in the cab very briefly, so I thought maybe the heater core might be leaking or plugged, but did not want to tear it apart if it was something else. Any ideas?

[daustin]

You might have a leak that only appears when the engine is hot. Might be a heater core/hose issue as well. These engines don't like getting hot, prone to cracking. I'd make that a priority to find, get it nice and warm and see if you can find it then. I've used the liquid detector/dye stuff at times for a sneaky leak. Good luck
Don

[rustyk]

It's obvious you have a leak, and you need to find out the source. A coolant smell in the cab is most likely caused by a heater core issue (or if you're lucky, a bad hose; sadly, those rarely result in the odor in the cab).

The A/C condenser drain should be examined for signs of coolant, and if any is present, you get to enjoy the pleasure of replacing the heater core. GM has never made this easy; I replaced one on my since-sold Chebby G30 van-based RV, and it took about 5 hours. Did the same on my Ford E-350, and it took 45 minutes...

[chickenhunterbob]

If your 94 is like mine, the heater core is painfully simple to replace, remove the cover on the passenger side of the cockpit on the floor inside the cab, remove one bolt holding a clip and disconnect the hoses on the engine side of the firewall.

Unfortunately, that seems not to be your problem, if the heater core leaked 3/4 gallon of antifreeze, you would have a puddle of 3/4 gallon of antifreeze on the floor on the passenger side of the cockpit.

You would not smell coolant briefly, but rather you would have to hold your head out the window to breath, and the windows would be all fogged up.

Check for drips where you park, and have a good look around the engine compartment, paying particular attention to any apparent signs of leaks at the water pump weep hole, any hoses, the radiator itself, if the lower shroud has any coolant, etc.

Check your oil for signs coolant (milky, rise in level) and Smell the exhaust, worst case scenario is that the coolant is ending up in the combustion chamber, or crankcase.

[16gaSxS]

A couple of other thoughts, check around the shaft of the water pump, I have had that happen with a fairly new pump. The other thing is if you have the worm gear type hose clamps try tightening them all. After replacing hoses I had a slight leak a few months later, after the truck warmed up and found the clamps were no longer tight. I tightened them all and leak went away.

[tom yuenkel]

as I went throught this myself this is what I did; I found it easiest to see that leak during intial warm up before the coolant begins to vaporize. I shut it off after only a few momments then crawled around and checked for leaks, also alot more obvious during the winter months.