How To Replace An 80 Series Thermostat?

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Ugly Dwarf

Ugly Dwarf

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10 Year
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Apr 13, 2012
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East Bay - San Francisco Bay Area
I've been searching the 80's Tech and FAQ section for the last 30-45 minutes and found lots of posts where people state they changed their thermostat, but haven't found anyone who describes the process in detail.

Can anyone point me to an existing thread that gives step by step details on how to replace on the 1FZ engine (I have a 1994), preferably with pictures? This may give away too much about my experience here, but I have zero idea of where to look for the thermostat or what I should do in addition to replacing it (other than using a new gasket when I do).

I'm currently in the process of doing a ghetto coolant flush, where I have been repeatedly draining the radiator from the petcock valve, topping off with distilled water, running till the thermostat opens, running the heater and rear heater for 15-20 minutes, turn off / cool, drain, repeat. I'm about 6 iterations into the process and the water is coming out clear (well, a tad bit milky). Upon my final drain, I will plan to fill with up to 2 gallons of Toyota Red (100%), giving me an approximate 50/50 mix of Red/Distilled Water.

Upon the suggestion of a friend of mine here on Mud, I am planning to replace the PHH (ordered the 1FZFEPHH.com silicone kit today). I suspect the PHH was replaced when the HG was done ~25K miles back and I couldn't see any bulging when I looked at the existing PHH (which had cheapy hose clamps, not the fancy constant torque clamps), but I'm figuring to just do it and be done while I'm draining the system for the last time.

Anyway, any help or guidance on how to replace the thermostat and / or suggestions on any other cooling system things I should look at / replace while I'm doing this would be appreciated.

Thanks,

Dwarf
 
Super simple!

I took off the front heat shield that covers the exhaust manifold.

There's 3 nuts that hold the housing on. Just take em off and pull.
 
Thanks guys.

The pic at the end of Tom's link spoke WAY more than 1000 words ever could have...

... though it also created questions about what "O-Ring" was referenced in the same thread?
 
Its the O-ring that seals the thermostat housing, as opposed to a gasket as you mentioned. When you open it up you'll see it, but don't open it up until you have the new one.

Good luck.
 
Thx GB.

I've been thinking about this tonight.... Am I wasting my time and money replacing the thermostat at this point? The HG was replaced (by PO) about 25K / 6 years back. I took a look at the receipt (a stack of them came with the truck) and noticed the thermostat was replaced then.

From some other reading I've been doing this evening, it looks like this may be a part that can go a VERY long time without failing and often gives a warning before it goes.

Do you guys replace this as a maintenance item? Or is this something you replace when the temp gauge starts acting up / thermostat fails?

I'll note that my temp gauge holds pretty much rock solid from start up to 2 hours on the road (my longest drive so far in this rig) running the A/C on a moderately warm day.
 
Make sure you have an OEM Tstat in there.

As scottryana noted, this is a pretty easy job. Since you are flushing the system anyway, I would replace it with a known OEM one and make very sure it is installed correctly (but that is me...). Heck, you can even pre-test the new one to make sure it opens and closes at the correct temps.
 
Ugly Dwarf said:
I'll note that my temp gauge holds pretty much rock solid from start up to 2 hours on the road (my longest drive so far in this rig) running the A/C on a moderately warm day.
Click to expand...

This is a 'feature' of the temp gauge. It holds in the same spot from something like 160 - 210 degrees. There's a mod for the 95 - 97 models but I'm not sure if anyone did the earlier models. Check the FAQ for RavenTai if you want more info.
 
Change it out with an OEM. I did mine for peace of mind and they had some stupid knock off in there. My Ultragage has been reading consistently 5-10f cooler since I replaced it.
 
Looking for a 190F T-stat that would fit a 96 hdj81. Anyone know the correct OEM one that fits that temp range?
 
Try partsouq dot com; put in your VIN and the correct parts diagrams for your truck will come up. Should be in the section titled Radiator and Water Outlet.
 
anyone ever find the draincock,or just pull apart the lower rad hose?
 
It's been a long time since I did this, but as I recall the draincock on the radiator faces rearward on the driver side. It's small, not super easy to open if it's been a while, and it drains very slowly.

That said, this thread is for an 80 series and it looks like you're in a 100 series from your signature line. Not sure if it's the same, but probably similar.
 
Make sure the jiggle valve on the tstat is in the 12 o'clock position when you put it in.

IMO, a section of gates green stripe or oem toyota hose for the phh, not silicone.
I like good quality ss hose clamps with rubber hose.
Also do the FHH just in front of the PHH.
OEM hose available through toyota.

If you're heater valve is looking tired, just replace that along with the attached hoses as well.
 
MUDZLLA said:
anyone ever find the draincock,or just pull apart the lower rad hose?
Click to expand...
I just found mine today. Can take a pic in the morn if you still need it. Was about to pull the hose myself!!
 
HardyDanger said:
I just found mine today. Can take a pic in the morn if you still need it. Was about to pull the hose myself!!
Click to expand...
Pulling apart the lower rad hose worked for me, but yeah would be interested in a pic!
 
Hard to take a pic of, but the screw driver tip is in the port. My battery box and ps hoses are out
4960BB40-BF5E-48D7-A5A2-946EDF16524B.webp

seen from below. (I have my oil cooler lines off) which are usually in the way). And a pic of the plug.
D966B4FD-8D4C-4B3E-A182-EBE20CF2AC45.webp

679EA6B6-7A33-4741-A5F9-A5B71111DB29.webp
 
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