FJ40 Thermostat Installation How To

[Nolacajun75]

Okay so I filled everything up with 100% distilled water. Ran it burped it ran it. Checked the temperatures with a laser pro lp300 infrared thermometer I started at 5:35 p.m. at 5:40 p.m. on the gauge it showed almost all the way to hot but not quite. It was at the last tick mark to the right side at 5:45. It went to Max hot.

I did take the wire going to the sending unit off to verify with power on the truck it showed nothing and it did show nothing. I grounded it and it did max out and stave max out even after I removed the wire. I turned the key off and the gauge went back to low temp with the wire plugged back into the singing unit like normal. When I start the truck it showed cooled like normal and it slowly crept up and got hot. Didn't Spike real fast. Just slowly went up well within 10 minutes. That's pretty quick.

The measurements I took with the thermometer were as follows and this is all within 10 minutes of starting it top left of radiator 220° top right 230° bottom radiator and hoses cold thermostat housing 266° block drain 170° sending unit 210° the front driver side of the block on top 187 rear 189 and I also checked the passenger side of the block section below the spark plugs where the little x marks look like they're in the metal and the front panel measured 140° and the rear 175°

Still don't know if I really have a overheat problem or not. I turned it off cuz I was scared to let it keep going

Going to let it sit for a little bit. Burp it again pull the sending unit. Make sure that's filled up and topped off. Then try it again and see what happens. Any ideas? Any thoughts?

I'm not sure If the thermostat opened up but I would think so being that the housing was 266 and I have a 180° thermostat that I did verify I worked with boiling water before installing. Not quite sure if the water pump is working or not. Not sure how to tell

 

[Nolacajun75]

What are normal temperatures for these areas? I'm not sure if I'm overheating or not

 

[Nolacajun75]

Well I decided to try it again. I let it run for about 15 minutes and everything looks the same. The radiator finally got hot to the middle of the radiant about with the bottom portion of the radiator and bottom hose to the radiator is barely lukewarm. I squeezed the bypass valve and it could feel a little pressure and feels like some movement but the hose on the driver side that goes from the thermostat to the radiator. I never did feel that pressurize I'll flow any water. I even squeezed it while someone revved. The engine didn't feel any difference but I did feel slight very slight press a difference in the bypass hose. So maybe I have another thermostat that's bad two in a row. I don't think so huh? Or maybe the housing for the thermostat that I got from City racer is somehow not doing something correctly? I guess I'll try to pull the thermostat and run without it and see what happens and go from there

What do you think? Anybody? Anybody help?

 

[Nolacajun75]

Well I decided to try it again. I let it run for about 15 minutes and everything looks the same. The radiator finally got hot to the middle of the radiant about with the bottom portion of the radiator and bottom hose to the radiator is barely lukewarm. I squeezed the bypass valve and it could feel a little pressure and feels like some movement but the hose on the driver side that goes from the thermostat to the radiator. I never did feel that pressurize I'll flow any water. I even squeezed it while someone revved. The engine didn't feel any difference but I did feel slight very slight press a difference in the bypass hose. So maybe I have another thermostat that's bad two in a row. I don't think so huh? Or maybe the housing for the thermostat that I got from City racer is somehow not doing something correctly? I guess I'll try to pull the thermostat and run without it and see what happens and go from there

What do you think? Anybody? Anybody help?

Oh I did burp everything before. I ran it the second time. Put the funnel back on the radiator full of water and also pulled the thermostat just to release any air pressure and tighten it back up.

 

[John McVicker]

Just thinking out loud here…this is an old thread but it has some excellent information. I suggest rereading posts 1-4 once more, look closely at his pictures (like the one I stole, above), make certain you have installed everything correctly, t-stat not upside down etc.

In addition to the radiator, have you drained the actual engine block? This drain is on the US driver side & towards the back of the engine. This is an important step.

Oops, reread your post & see that you have drained the block. Still, reread those posts, look at his pictures etc. make sure you have done everything according to Hoyle.


EDIT: While you are doing all of this temp. testing etc. what are the outside temperatures? Is your fan belt tight? And do you have the fan shroud on the radiator.?

 

[John McVicker]

One more suggestion: Consider upgrading your FAN CLUTCH to a FJ80 FCT 049. You can purchase this from @cruiseroutfit. Don’t remember how much this was…prob about $100.

I’m not suggesting to just start throwing money at your rig, but this is a very popular upgrade, done by many on MUD, including me. It helps, no ifs ands or butts, and gives you piece of mind.

First do some research here on MUD & get familiar with this upgrade…AND… search on how to test out your current FAN CLUTCH. Very easy/simple.

 

[Nolacajun75]

Just thinking out loud here…this is an old thread but it has some excellent information. I suggest rereading posts 1-4 once more, look closely at his pictures (like the one I stole, above), make certain you have installed everything correctly, t-stat not upside down etc.

In addition to the radiator, have you drained the actual engine block? This drain is on the US driver side & towards the back of the engine. This is an important step.

Oops, reread your post & see that you have drained the block. Still, reread those posts, look at his pictures etc. make sure you have done everything according to Hoyle.


EDIT: While you are doing all of this temp. testing etc. what are the outside temperatures? Is your fan belt tight? And do you have the fan shroud on the radiator.?

View attachment 3631931

Yes, the thermostat is definitely on correctly exactly as the picture shown on both of my thermostat installs.

I do a fan shroud installed and it is installed correctly in flush. The same trial that was on my old original radiator and everything was fine with that.

Outside ambient temperature approximately 75 to 80° f

I'm going to pull the thermostat out and run with the thermostat just to see if it fixes the problem. If it doesn't then I know it's going to have to be a bad water pump that I installed even though it was OEM and new.

 

[Nolacajun75]

I'm starting to think I might have gotten a bad water pump that I installed. I don't know

 

[1911]

I'm starting to think I might have gotten a bad water pump that I installed. I don't know

In my experience, a water pump is a simple piece of equipment; they either work or they don't - and if they don't, they drip water out of the weep hole. In other words, I would be very doubtful that your water pump is bad. If it were bad, you would have much higher temperatures everywhere; it would boil over very quickly. I suggest that you can cross this off your list, since you have recently(?) installed a new one.

 

[Nolacajun75]

In my experience, a water pump is a simple piece of equipment; they either work or they don't - and if they don't, they drip water out of the weep hole. In other words, I would be very doubtful that your water pump is bad. If it were bad, you would have much higher temperatures everywhere; it would boil over very quickly. I suggest that you can cross this off your list, since you have recently(?) installed a new one.

I know I'd agree but just don't know what to do. Everything in the system is new with system. I guess our movie thermostat and run without it to see what happens. I'll post tomorrow after it's sealed and dried with results

 

[RevISK]

I know you said you burped, but I’ve had tenacious air bubbles after I swore up, down, left and right that I got them all out.

 

[Nolacajun75]

I know you said you burped, but I’ve had tenacious air bubbles after I swore up, down, left and right that I got them all out.

I know and I understand that, but with those temperatures I gathered with these laser thermometer. Do you think those are actually overheating temperatures? I did run it again for about 20 minutes just for the hell of it and the top of the thermostat was almost 300° on the outside of the metal at least, so I was pretty sure that didn't want to run it anymore

 

[John McVicker]

Still could be your FAN CLUTCH not having enough ‘resistance’ to pull enough air through the radiator. And if your fan clutch is weak and not up to par it would absolutely cause overheating.

STRONG SUGGESTION: Do a search on how to do the ‘folded newspaper’ test on a radiator fan. You can also use a folded up towel to do the same thing. That’s where you run your engine at idle and hold a newspaper up to your fan blades in order to see how much resistance you can feel.

Low resistance means it’s not able to pull the needed amount of amount of air thru the radiator, which equals overheating. Fan clutches get old & wear out. That’s why so many people replace them and/or add additional & heavier than stock silicone in order to have more resistance.

 

[RevISK]

I know and I understand that, but with those temperatures I gathered with these laser thermometer. Do you think those are actually overheating temperatures? I did run it again for about 20 minutes just for the hell of it and the top of the thermostat was almost 300° on the outside of the metal at least, so I was pretty sure that didn't want to run it anymore

I'm no expert by any means but that sounds too hot. It happens quickly, yes? I'd listen to John's advice above. Anyone with an avatar like that must know what he's talking about.

 

[Nolacajun75]

Still could be your FAN CLUTCH not having enough ‘resistance’ to pull enough air through the radiator. And if your fan clutch is weak and not up to par it would absolutely cause overheating.

STRONG SUGGESTION: Do a search on how to do the ‘folded newspaper’ test on a radiator fan. You can also use a folded up towel to do the same thing. That’s where you run your engine at idle and hold a newspaper up to your fan blades in order to see how much resistance you can feel.

Low resistance means it’s not able to pull the needed amount of amount of air thru the radiator, which equals overheating. Fan clutches get old & wear out. That’s why so many people replace them and/or add additional & heavier than stock silicone in order to have more resistance.

I don't have a fan clutch direct drive and I also did try the newspaper trick and there's no stopping that fan. It's blowing like crazy. I can even put a piece of paper in front of the radiator and it sucks it to the radiator so the fan is good

 

[Nolacajun75]

I'm no expert by any means but that sounds too hot. It happens quickly, yes? I'd listen to John's advice above. Anyone with an avatar like that must know what he's talking about.

I agree but I just don't know about the temperatures. Seems hot to me though. And no fan clutch. So the above mentioned doesn't apply, I really wish it did though. I'm about to pull the thermostat and try it later tonight with nothing in there just to see what happens for the hell of it. After that then it has to be the water pump. There's nothing else it can be.

I'm also going to order some head gasket testing equipment so I can check for combustion gases in my coolant and also do a leak down test on my cylinders to look for any type of head gasket leaks. That'll be my next step before I pull the water pump off but water flows freely from everywhere so not sure if I have any type of clog but I guess I can have a clog at the water pump even though I didn't see one when I installed it and it was everything was working fine with the old water pump. Or I could have a new blockage in the block somewhere that's not affecting the water coming out of the drainayy I don't know

 

[John McVicker]

Is there anyway you can borrow someone’s IR gun in order to compare the temps with the one you’ve been using?

 

[RevISK]

I agree but I just don't know about the temperatures. Seems hot to me though. And no fan clutch. So the above mentioned doesn't apply, I really wish it did though. I'm about to pull the thermostat and try it later tonight with nothing in there just to see what happens for the hell of it. After that then it has to be the water pump. There's nothing else it can be.

I'm also going to order some head gasket testing equipment so I can check for combustion gases in my coolant and also do a leak down test on my cylinders to look for any type of head gasket leaks. That'll be my next step before I pull the water pump off but water flows freely from everywhere so not sure if I have any type of clog but I guess I can have a clog at the water pump even though I didn't see one when I installed it and it was everything was working fine with the old water pump. Or I could have a new blockage in the block somewhere that's not affecting the water coming out of the drainayy I don't know

It really still could be a small amount of air stuck in the system somewhere or as you surmise, a clog/blockage.
I flushed the utter bejeezus out of mine and was still only able to get a fraction of the coolant in it was supposed to have. Did a thermocure treatment and flushed again and bunch more crap came out. I was then able to fill with the proper amount and then I went on my own burp saga, took quite awhile and as I said previously, ended up still having air in there.

How much coolant were you able to put in?

 

[John McVicker]

Agree with @RevISK .

And @Nolacajun75 when you were burping did you also have the front end of your truck raised up? Doing so helps the process.

 

[RevISK]

Agree with @RevISK . And @Nolacajun75 when you were burping did you also have the front end of your truck raised up? Doing so helps the process.

I had to position my truck at around 50+ degrees nose up to get all the air out. Hopefully it's as "easy" as this? Also helps to squeeze every hose everywhere.