My 1990 v6 Toyota pickup loses most rad fluid overnight, but it just passed a pressure test for leaks? how?

Question

after overheating, mr lube mentioned i must have an airlock and tried bleeding air out while adding fluid as my truck ran.. without overheating, the rad volcanoed fluid and wouldnt accept any more than 1/2 full without spewing it out everywhere... mechanics did a pressure test and found no leaks, changed the t-stat, but it leaks hardcore overnight while parked, without overheating.. whats going on?!

Answer 1

Okay just for the fun of it, tomorrow morning before you ever start the engine up , raise the hood and pull the oil dipstick and see how it reads ,is it super full ,does it have white looken oil like water has been in it.If all of this checks out ok then your problem is going to be a bad water pump, A water pump has a hole in it so when it gose bad it will leak water out even when the car is setting there over night.         ( Check that water pump out.)

Answer 2

i'd have them do another pressure check.. its going somewhere .. so theres got to be a leak ..

Answer 3

ok, we all know that these V-6's are prown for headgasket problems.  A pressure check is not accurate in checking this.  Have someone do a block check (chemical check) for hydrocarbons (exhaust gas) in the cooling system.  You sound like you have a blown headgasket, this is common.

Good Luck

Answer 4

It leaks where?  All over the ground under the car?  It still volcanoes out the cap after you put a new thermostat on it?  Do you see coolant anywhere under or around the engine?  There is a water jacket on top of the engine that the upper radiator hose bolts to.  It goes thru the timing cover and bolts down to the front of the intake,  is there any coolant puddled around this?  If not, I would assume you have a blown head gasket, which is common on the 3.0L.  Next you will see a lot of steam coming out of your tail pipe.