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Old 11-20-2008, 01:01 PM
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RicardoJM RicardoJM is offline
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Join Date: Jul 2007
Location: Centennial, CO
Posts: 2,398
Default FJ40 Thermostat Installation

After putting around with my project for the past 10 months, more and more things are making sense and coming together. After putting the heaters and new hoses into the truck this weekend, the heat was not consistent. Even after the truck had been running 20 minutes, sometimes the heat would be really hot and other times it was just barely warm.

I did some research on our board (thanks Subzali) and MUD and developed a short list of suspect causes for why the coolant temperatures would be inconsistent.
  • blockage in radiator/heater cores - ruled out as radiator was replaced in January and heater cores were inspected by the radiator shop
  • blockage in hoses - ruled out as all radiator and heater hoses have been replaced
  • bad heater valve - ruled out as it had been replaced with an OEM that was cleaned up and works smooth as butter
  • blockage in block – ruled out as I have not experienced overheating
  • head gasket leak - possible
  • cracked block - possible
  • flow by a missing o-ring - possible
  • bad thermostat - possible

I should have checked the radiator level prior to re-installing the heaters. I had some hose connection issues during the reconnect process so in addition to the additional coolant needed to fill the heater cores and their hoses I had to account for the ¾ gallon of coolant I lost through loose hose connections on the rear heater when I opened the heater valve. I will be keeping a closer eye on my coolant level and make a mental note to check the level of stuff more often and especially before draining. Because of this, I could not rule out these items as being contributing factors to the the inconsistent temperature problem.

Next on the list would be the o-ring and thermostat. Here is where the embarrassment comes into play; because “replace the thermostat” is near the top of every "baseline your truck" list that I've seen. In my case the truck never overheated and the temperature gauge always ran towards the lower end of the scale. So replacing the thermostat moved down the list into the range of "someday I really need to get around to that" projects.

I dropped by Burt on my way home Tuesday and picked up a thermostat, gasket and o-ring. That evening I sprayed the thermostat housing bolts with PB Blaster as my research indicated these are bolts can be a PITA if they break. I noticed that my thermostat housing cap did not have two bolts. I had on bolt and the other was a threaded rod with a nut holding the housing down on its base. I was not expecting to see that, but it was clear the nut would need to come off, so bolt and nut got the full PB Blaster treatment.

Yesterday afternoon with my youngest son Randy working the wrenches we tackled the job. As most of you know, even something as straight forward as "remove one bolt, remove one nut, lift up the housing, remove old stuff, put in new stuff" can end up being not so straight forward. This was one of those projects. Randy was working the wrenches and the bolt came out just fine. On the threaded rod, the nut came off easy, but the threaded rod was too thick for the thermostat housing to slip up and off. We disconnected the hoses from the thermostat housing top to eliminate any tension they were putting on the housing cap. With the hoses off we were able to rotate the housing a little, but side to side motion was not making any improvement in our need to get up motion.

The good news is that it takes me less time to come to grips with realizing that conditions warrant improvisation. In this case, we needed to get the rod unthreaded and the typical improvisation options for the situation include; double nut or vice grips. We ruled out the vice grips because of the potential damage to threads and decided to give the double nut a try. Randy thought it was cool that with the two nuts snug together we were able to unthread the rod. I thought it was cool, that I remembered from my front disk brake conversion that double nut is used to insert/remove threaded rods, aka old style knuckle studs.

After getting the threaded rod out, the thermostat housing lifted right up. With the housing off, it was instantly clear that we were progressing towards resolving the inconsistent temperatures. There was no thermostat or o-ring in the housing. We installed the new gasket, thermostat and o-ring and even found a suitable bolt in the jar to replace the rod. With everything buttoned up and the hoses reconnected, we topped it off with coolant and ran the truck on the driveway incline to burp the air. Randy was in shorts so he sat inside the truck monitoring the temperature guage and confimring the heaters blow hot air I was outside confirming the hoses were holding and there were no leaks.

It is still early, but during the burping process and driving to and from a meeting last night, the heat level is consistent – and hot. The temperature gauge starts out cold and rises right up into the middle of the gauge. I still may have blockage in the core, head gasket leak, and/or cracked block issues in my future. I also may have issues from running the truck with no thermostat. However, I am content that I understand how my cooling system works, what its current condition is and that I have heat that works.

In writing up this post, I am wishing I had taken pictures of the process, in particular what the threaded rod and bolt looked like and the double nut technique to get it unthreaded. A picture of the pool of green coolant just sitting in the bottom half of the thermostat housing would also have been cool. That said, with darkness coming so early Randy and I were more focused on dealing with the wrenching while we had natural light. In retrospect, we were at it an hour past sundown and did just fine with a work light.
Ricardo Maestas - Bio Page
1999 LX 470
SOLD - 1971 FJ-40
TLCA #18941
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