Hello yota community!

The long title is"22-re coolant builds pressure/then overheats when driving on the freeway 60-70mph". I have replaced lots of parts and done some troubleshooting and can't figure out what is making my truck do this.

It's a stock and well maintained 1994 SR5 4X4 Extended cab. When I drive at freeway speeds the truck overheats and when I pull over the coolant is super low. It appears to be going out to the reservoir then out the overflow tube. If I drive around town it isn't a problem. It started off and on but now I can't drive on the freeway for more than 20 miles consistently. When it started, I could drive hundreds of miles and it would change from one day to the next.

I don't know if this is related but the truck has a new head gasket as of two years ago. It didn't have a head gasket leak at the time. One of the valve springs had broken. I used OEM parts. It didn't overheat before I did the job.

A year later I am having this annoying overheating problem.

• block test is negative every time I test
• new oem fan clutch
• new oem water pump
• new oem heater valve
• new thermostat w/ 1/8" hole drilled in it twice. no change
• new radiator
• new radiator cap twice. no change
• 3-6 years ago new oem IACV
• hoses are not collapsing
• heater core bypassed with no change
• burping system with truck parked going up hill- no results
• 175psi in all four cylinders. pressure holds

I think it makes sense to do the head gasket again. I'll get it decked and pressure tested like last time. Maybe I'll find something weird. I also think I'm crazy.

Thoughts?

Here's a pick from when I got it 12ish years ago. Hawk. 175k on the ticker.


Here is a more recent photo. 320k on the ticker.

 

Wow, after all that, the only thing I can think of is you have enough flow to city drive but restricted/weak enough to cause thermal runway at highway speed. Idk. Maybe run a radiator flush to clean block journals? Maybe damage to interior mating surface of waterpump or gasket causing an internal bypass? Impeller inverted? Lol, following too close and not sliding out of slipstream to let radiator breathe when on interstate? I'm scratching my head too. Keep us updated.

 

To me sounds like a head gasket leak.

 

That’s a classic head gasket or a cracked head bleeding into the coolant.

 

What brand headgasket?

 

The surfaces, save for the block deck, are all in good shape.

 

OEM head gaskets every time.

 

Rads been flushed and now replaced. All surfaces, save for the block deck, are in great shape.

 

I would normally be pretty quick to agree with you.

It passes a block test every time, there is no coolant in the oil and no oil in the coolant. The cylinders hold pressure and the cooling system holds pressure.

Do you still think it's a head gasket or cracked head?

 

I would normally be pretty quick to agree with you.

It passes a block test every time, there is no coolant in the oil and no oil in the coolant. The cylinders hold pressure and the cooling system holds pressure.

Do you still think it's a head gasket or cracked head?

 

What does a radiator flush look like to you?
Ive ran a hose through it with the drain open.
One thing i havent tried, that i should do this week, is flush the block journals behind the bung on the block by the bell housing. I saw it on the you tubes! Its nit something ive messed with before but a friend said he cleaned the galley on his 22RE block via that hole.

I dont suppose i could do much but its worth a shot. Heck, maybe i can slam some CLR in there on a pipe cleaner or something...