You can literally put the heads or head gaskets on the wrong side. If the HG is on the wrong side it will block the coolant passages.


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The heads are not side specific (though, the location and parts you install on them are different).

5VZ Cylinder head differences

-Charlie

Yep, I screwed up and put the heads on the short block on the wrong sides. Didn’t notice it until I went to install the intake……


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Thanks again, I ended up doing this and it was indeed easy and quick. The most annoying part was draining the coolant and removing my dynamic tensioner (sits right in front of the thermostat housing)


When i pulled my T-Stat out it was @ 6 O'Clock. I must've been watching Tim's vids or something =p


Good point! It's only about 2.5 years old so I hadn't considered it but it's not oem so maybe it's on its way out already? it looks good and feels good but idk how to tell if its good.


Update: after removing the T-Stat and going for a short test drive with the limited time I had with the car today...
The temp gauge sat at 25% (1/4 from the bottom) the entire time. Before pulling it out i got close to red within a mile.

What can I deduce from this observation?
I believe it's telling me that either the thermostat is bad (it's only like 2 years old 170 degree unit from URD) or, as I have been suspecting, there is some blockage not allowing coolant to flow freely. Also not totally abandoning the possibility that there is still air in the system or something (even though i filled/burped with a no-spill funnel)

What are my options for next steps?
Seems like maybe (in no particular order):
- a chemical flush to clear the potential blockage in the junkyard-sourced head.
- new T-Stat already???
- leakdown/compression tests

Also I got a new bluetooth scan tool so I'll be monitoring temps via Torque app from now on

I say try the new T-stat and rad cap and see what happens. Make sure you’re not sucking your lower rad hose flat. Also make sure your temp selector is on max heat to push any air trapped in the heater core into the rad.

Make sure your hose between the rad and overflow tank is not blocked and is tight on the barbs.

If your cooling system is operating properly the air should naturally purge into the expansion tank after around three drives.

Driving around, any air in the system will collect in the upper radiator tank.

When the engine cools off the rad caps vent valve relaxes. When you start the engine the water volume expends and that will push any air collected at the top of the rad into the expansion tank via the vent valve in the center of the cap. That valve is temperature sensitive. So when hot coolant starts going through the vent it closes to allow the cooling system to build pressure.

All three 3gen 4Runners I bought had a broken rad cap. I’ve had a Napa cap in my 97 for 3+ years without any issues. But, saying that everything is new. Engine, rad, etc.


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Glad you got the gasket made.
I'm confused about having to remove a dynamic tensioner.
Other than draining the rad I've never has to remove anything else to remove the thermostat housing.

You can check your current thermostat in a pot of boiling water.

My lower rad hose is actually bent a little extra because of the 1.5" body lift. I'll have to make sure it's not going flat. Thanks for the tips and the education on cooling system operation!


It's for the supercharger's drive pulley. It sits directly in the way of the thermostat housing. I'll check my thermostat as soon as I can find a thermometer thanks for the reminder I totally forgot I can do that

How old is your Rad since you have a supercharger on it? If it’s never been replaced I’d replace it as well, unless it looks super clean inside.

For the record I’ve never had to “Burp” a cooling system.

The closest I ever got was my 04 grand Cherokee with the 4.7 V8. There is a high spot in the engine that collects the air. And *****footing won’t push the air into the rad. So I did some spirted driving after the engine got fully up to temp. The high rpm’s pushed the air pocket into the rad. That eliminated the waterfall sound from my heater core.


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The radiator, radiator cap, and thermostat are all ~2 years old.

I couldn't do any spirited driving as I overheated in the first mile of neighborhood driving on my previous test drive (before pulling the thermostat out), but that sounds worth a try once i get it healthy enough to do so!

I tested my thermostat today.

Here's a short video showing the results: 170 degree Motorad Thermostat operation - YouTube

I couldn't find any other videos showing how it should open at a given temperature, so I'm not totally sure what to conclude from the test but i can at least say it opens. It cracks open later (~178 degrees) than it's rated (170 degrees) then doesnt really open wide until nearly 190 and fully open at 195+.

Like i said, idk if that's completely normal operation, but it does open and shut.

If we can agree that the thermostat is working well enough, the only things left to do is make sure the lower hose isn't collapsing (it's already more bent than normal because of a body lift) and take it to a shop for a chemical flush. The coolant passages on the head that wasn't replaced, the block, the radiator, and everything i could see when i had the heads and water pump off looked very clean. But the junkyard head that I put in had coolant passages that looked like they had a lot of crap in them... I really shouldve had that cleaned out when it was at the machine shop.

Pressure tested the cooling system today.

After applying pressure to the system I was able to see a super obvious leak in the upper radiator hose that somehow didn't show itself before.

I guess when the coolant is hot and flowing the leak would allow air to get in but not coolant to come out. Then when I pressurized the system, the coolant was static so it easily came out where air was getting in.

Ok.. tightened the hose clamp. It broke. Put a new one on and now system holds 15+ psi solid for 20min. In retrospect the dial on the gauge was sticky so it could have been leaking pressure slowly and not showing on the gauge...

Anyways, I'll throw the thermostat in next and see what happens!

The thermostat will stay closed, if you're just pressurizing the system with a pressure tester. You need to get it up to the operating temp of the engine. 190° F I think is right, but I may well be wrong on that.

Also, the kind of hose clamps that come from the factory, the clamps Toyota puts on, seem to work better than the screw down clamps you get from the auto parts store. They are readily available from Toyota parts sources.

Good fortune to you!
Pat☺

I thought pressure would hit both sides of a closed thermostat because it's going in both directions unlike coolant flow which goes in 1 direction. Either way, my thermostat is still out so I didn't have that problem lol.

Thx for the tip on the clamps I'll see how much toyota wants for them!

Finally got some time to work on the 4runner today...

I put the thermostat back in, bled/burp using no-spill funnel, heaters on, etc...

With the heaters on full blast I'm hovering at 195-198°F. As soon as I turn them off I start creeping up to 205+.

My lower radiator hose stays cool to the touch the whole time, sounds like my t Stat is either opening too slowly or not opening as much as it should.

I thought my test showed that it was working bit I guess not as well as it should be. I'll order a new unit and test it before install so I can compare the behavior

Don't try that test in the summer. The heater core is a reasonable fraction of the radiator in size (maybe 1/8 or so?) and its coolant flow bypasses the thermostat. Your test is showing there is no (or near no) flow to/from the radiator. Even when run 'upside down' the thermostat will keep the engine below 205*F, especially at idle.

-Charlie