Matt16

Theoretically it is possible to have an air bubble in the system and the coolant to appear full then suddenly empty. Bubble stuck at a high point in the system, eventually works its way to the rad cap (another high point) where it is forced out the the system by the pressure in the system through the cap and into the overflow (not airtight seal) and escape. The engine cools off and sucks the remaining overflow coolant back into the system leaving it empty and the driver very puzzled... right?

Almost certain it is not the HG as i did that carefully a little over a year ago and the exhaust doesn't smell sweet, no steam etc... Might be a leak, there are still several hoses that are probably original, just I have my doubts they would allow the escape of a little of fluid in 15-30 miles. Its done this before after I've messed with the cooling system. 'll have a better look tmr.

By the way, I don't know if it was by design or fluke, but I LOVE how the heater core "gurgles" at me when the coolant is low. Lets me know I have to check it.

vital22re

iTrader: (2)

The only way I see that possibility happen is just after working on the cooling system, where you had to drain and fill the radiator. But if you havent' done any recent work on it.. then i'd say you have a slow leak. Try to get your hands on a coolant pressure tester. good luck.

Matt16

I should have mentioned that I replaced the lower rad hose (rad to pipe) less than 20 miles ago.

desert-rat660

are you on pins and needles about the possibility of a head gasket being blown?

Matt16

Not really. Now's about the best time it could happen if that were the case. I can bus to work and no studying as I'm not in school now until September. Also have money for parts now that I don't during the Sept-Apr period. I could slap on a new HG over a long weekend.

Also, I've got no white smoke and the exhaust smells like it usually does. Oil is not milky either. My guess is air in the system.

T-1000

Make sure you check the stupid petcock, mine got loosened. It was driving me nuts.

I also put two hose clamps on the ends of my big radiator hoses, make darn sure nothing it leaking there.

Matt16

I refilled the rad and reserve and drove 60km (35mi) today. Didn't use a drop of coolant aside from when I kept checking for bubbles by opening the cap when the engine was hot and the truck was facing uphil. I think its pretty well burped by now.

desert-rat660

well thats a good thing, when i did my HG it was a PITA. one of the head bolts snapped off part way in the head, so i couldnt get the damn head off the block

4runner4life93

get a new rad cap