Moved from All Questions thread.

Just finished my head gaskets and the truck is running much better than before, smoother idle, no more hesitation, and no more white smoke. but I'm having some overheating issues. Doesn't overheat idling, only while driving. If I stop at a light or stop sign and raise revs in neutral the temp will go down a bit.

There's a new oem water pump, timing belt, thermostat and fan clutch.

I've burped the system using a no spill funnel while parked on a hill.

The only thing left I can think of is clogged coolant passage or I seriously fked something up doing the head gasket. But the car feels like it's running better than ever except for the overheating issue

What else could I be missing?? Would having the tstat jiggle valve in the wrong orientation cause this much of an issue?

I havent pressure test the cooling system or compression check yet, I guess that's next up.

The thermostat jiggle valve in the wrong orientation, which would be in the 12 o'clock position, will cause your engine to run approximately 10 degrees hotter. It's a decent difference, but not enough to cause the engine to overheat. A normally functioning cooling system on the 5VZ-FE engine will run between 188-192, but will go up depending on the ambient temps and driving conditions.

What temps are you seeing? Are you consuming any coolant?

I'll need to get a scan tool. I haven't been able to drive long/far enough to lose coolant as I see temps creeping up toward the red within a mile. When I first finished I was able to drive a couple miles (albeit down a mountain) without overheating, but it seems like as soon as I put any load on the engine at all it begins to overheat. Sometimes it'll come back down before reaching red (not sure what triggers that) but I have to be ready to pull over at any moment

Were the cylinder heads inspected/tested for cracks when the head gaskets were replaced? I would also check the oil to see if there are any signs of coolant in it. I'm guessing you either still have air in the system or something was missed during your headgasket repair.

Good luck and let us know what you find.

You say head gaskets so I'm assuming it's the V6.
Are you sure you put the left gasket on the left head and the right gasket on the right head?

OBDII-based temp reading is crucial info you need. You want to know where your temps stand more accurately than the "Cold, OK, and Disaster" the dash gauge provides. Is there action in your overflow jug? Is your coolant actually hot AF? Dash gauges can go crazy (fuel for example).

I see action in the overflow jug. Coolant goes into the overflow when hot. If i start it hours later when completely cool it gets sucked back up into the radiator.

When the engine gets hot and i turn it off i can hear a lot of boiling/bubbling/gurgling inside the radiator/hoses

You may still have air pockets inside the engine block.

It should suck back in on its own while the engine is off and cooling down - it shouldn't require the water pump to suck it back in. Cold to hot the overflow should go up and down maybe half the height of the overflow container.

-Charlie

Does your overflow always go back to the same cold level?

Generally three heat cycles with a properly operating rad cap should push all the air out of the system.


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Not sure but thanks for that insight, i'll monitor that


I need to try and get the truck mobile so I can get back to my garage so I can figure this out. But my house is 25 miles away up a steep mountain so it'll take all day to limp there.

I want to try running without the thermostat and see if that'll get me home or at least to a shop.

The gasket/o-ring is on the thermostat so will the neck leak if I remove the thermostat?

BTW I got a scan tool so I'll grab some helpful data next time I'm with the car

One of my heads was visibly cracked so i sourced a junker which the machine shop inspected, pressure tested, and machined. One thing that got skipped out on is clearing the coolant jacket of the junker head which looked like the underside of an old boat.



I didnt know there was a left vs right! i just made sure that all the alignment dowels lined up and no holes/ports were covered. I would imagine that it would have more severe symptoms if they were backwards right? It can idle without overheating and drives as good as ever besides the overheating ofc

If you have an old thermostat around you could gut it and then you'd be able to use the oring.

Or, you could make a gasket out of paper type gasket material or even the right kind of thin cardboard.
There's various technique's, all of them easy and quick.

And to repeat what Tim said - when you figure this out and put in the final TStat, make sure the jiggle valve is down at 6 O'Clock. My temps dropped 13 degrees immediately after doing so. I had swapped in a new radiator and oriented the TStat the way the previous mechanic had....wrong.

New OEM radiator cap too?