Toyota Thermostat Installation Position Tip

[Lewis]

Genuine Toyota 90916-03075 Thermostat​

We had a Toyota vehicle towed into the shop the other day and the customers complaint was that it was overheating. The repair shop replaced almost everything in the cooling system and still had this issue so the customer wanted us to step in.

We knew from talking to the customer that the shop was using aftermarket parts, so after inspecting the outside on the cooling system and not being able to find any visible leaks (the cooling system was full) we decide to start inspecting the parts that were replaced. The first items we could easily get to were the thermostat and water pump. These two are very close together and we could inspect both at the same time. The problem we encountered was with the thermostat positioning. Here is a shot with the housing removed...

As you can see, the "jiggle" valve is positioned straight down (6 O'clock position) which doesn't allow for trapped air to bypass the thermostat. This creates a air pocket in the cooling system, specifically in the block.

While we were there we used a electronic bore-scope to we if the water-pump fins were intact, and not loose.... they were fine....

So we decide to installed a new Toyota OEM Thermostat, this time installed correctly. This is how Toyota thermostats are advised to be installed by the repair manual...

So after installing the thermostat correctly.... the vehicle was fixed....

Always remember that the thermostat's "jiggle" valve is designed to let any air trapped in the system work its way back to the radiator/overflow tank and it's positioning is important.

 

[Noah Mckinnon]

The field service manuals for Toyota trucks with the 5vz-fe engine (mid 90's mid 00's Tacomas, T100's, Tundras, 4-runners) say to place the jiggle valve in the down (6 o'clock) position. You'll find a lot of owners of report on various enthusiast forums that the jiggle valve in the down position for that engine results in an engine temp of ~190F whereas putting it in the up makes the engine run ~200F. I can confirm this as I just had my 03 Tacoma V6 serviced and they put the valve in the up, then later in the down when I brought it back saying my temps were running about 10F hotter than before I brought it in. I read up on thermostats and jiggle valves and I still don't understand what's going on here. Can you explain?

 

[Lewis]

I think the worst advice is to put it back in the same position as you found it. Who knows what the last repair technician was thinking when they did the work.

I can't explain what is going on with your truck (and others) when its reported that there is a 10 degree difference. I take your word for it but cant see how. I would think that your results would be opposite of whats being reported. I did some research on this and found you are correct in the older 5VZ's with the repair manual showing it facing downward.
I also found that the newer recommendation by Toyota and Stant advise it up in the 12 o'clock position.

My advice would be to follow the repair manual.

 

[Ed Brio]

I can confirm the thermostat position confusión in the toyota 5v. As soon as I turned that sucker around, my Toyota 3.4 ran 10-15 degrees cooler.

 

[Dave98]

I can confirm the thermostat position confusión in the toyota 5v. As soon as I turned that sucker around, my Toyota 3.4 ran 10-15 degrees cooler.

Ed- at the risk of appearing dense, please tell us what you “turned that sucker around” from. Was it at 12 o’clock and you put it to 6 o’clock or the opposite? Exactly which final position gave you best results? Thanks

 

[Shawn]

I can confirm the thermostat position confusión in the toyota 5v. As soon as I turned that sucker around, my Toyota 3.4 ran 10-15 degrees cooler.

I have to ask so where was your final position of jiggle valve. 12.00 or 6.00 oclock

 

[Amarts]

I can confirm the thermostat position confusión in the toyota 5v. As soon as I turned that sucker around, my Toyota 3.4 ran 10-15 degrees cooler.

Um, Eddie? What position was it in BEFORE you turned it around.

 

[William]

The field service manuals for Toyota trucks with the 5vz-fe engine (mid 90's mid 00's Tacomas, T100's, Tundras, 4-runners) say to place the jiggle valve in the down (6 o'clock) position. You'll find a lot of owners of report on various enthusiast forums that the jiggle valve in the down position for that engine results in an engine temp of ~190F whereas putting it in the up makes the engine run ~200F. I can confirm this as I just had my 03 Tacoma V6 serviced and they put the valve in the up, then later in the down when I brought it back saying my temps were running about 10F hotter than before I brought it in. I read up on thermostats and jiggle valves and I still don't understand what's going on here. Can you explain?

 

[William]

I've recently had to replace my radiator on my toyota prado landcruiser 1997. I replaced the thermostat and hoses as well. the owners manual said the same. Place the jiggle valve at 6 o'clock. I did notice when I changed the thermostat when I first got the car that the jiggle valve was at 12o'clock. So far there has been no significant change in the temperature gauge or performance.