Hi All,

I have a 99 F150 4.2L with 115k. Other then a heater core...what else would cause the coolant to disappear?
On Friday, after the truck was warmed up, the heat in the cab went cold. I messing around with the controls while at a stop light and noticed that the temp gauge started to climb. I pulled over and turned the engine off. I opened the coolant tank and released the pressure. The tank was about 10% full. I picked up some coolant and dumped it in and brought it to the shop to have a pressure test done. The tech said that the system held pressure with the engine off and running...

Can anyone think of what to check next? I am still loosing coolant when I drive.

Thanks!!

 

Look really close at the water pump. Go ahead and put a new cap on the reservoir due to the age of the truck. Add dye to the cooling system and look for a leak with a black light. Look really close at the head gaskets. The 3.8/4.2 are notorious for head gaskets leaking.

 

So you don't think that there is any chance of it being the heater core? The tech suggested that there might be a small hole that closes when the truck is at operating temperature.

I'm not sure what is worse, heater core or head gasket...

 

Could be a heater core. Thats why you put the dye in it to see the dye trace and find the leak.

 

Usually a heater core will leak into the cabin. Did the mechanic you took it to check the oil. Go check it yourself and see if it looks foamy. NGM, i think you know what I'm talking about but I dont want to drop the bomb yet. No reason to induce panic. Is the truck making puddles, or the coolant is just disappearing.

 

There aren't any puddles. The coolant just disappears. I checked the oil and there wasn't any signs that it was leaking in there.

It's at the shop right now for a dye test. They are also going to do another pressure test from a cold start to see if there is any change there. I should know by 9:30 EST. I will update the post.

 

Good news... kinda. Turns out that when they did the cold pressure test, at 10lbs of pressure, coolant sprayed out of the block heater onto the manifold.

They replaced the block heater and did another pressure test and no coolant leaks.

Here in Ontario, Canada a core heater replacement is approx. $900 (82/hr for labor). I only had to pay $116.13


Thanks for the help!!