FJ40 w/rebuilt 2F engine after sitting for several years, now have overheating issues (1 Viewer)

[FJnewlife]

Hello,
Sorry for the long post but I'm hoping it provides enough detail...
I have a 1977 FJ40 that sat in my garage for 20+ years with the engine pulled while waiting for me to find time & $$$ for a dream V8 conversion with an Advance Adapters kit, Ranger transfer case, power steering ...etc. I finally settled last summer on just having the original 2F engine rebuilt by a machine shop a couple hours away. Then later, I discovered a closer Land Cruiser shop & let them do the re-install. The very day I got it back, I didn't notice the temp gauge climbing and it got seriously hot to the point the local shop had to replace a couple valves and resurface the head but even after that, it continues to have overheating problems and the local shop is out of ideas. In cooler weather (50ish & lower) it runs fine with the temp needle settling between the first & half marks but when the weather warms up & within just a few miles the gauge climbs steadily & will go over the 3/4 mark if I don't pull over & let it cool or coast downhill in neutral. On one trip, the gauge was nearing the 3/4 mark and I was looking for a place to pull off when I noticed it settle back down suddenly so I thought AHA, the thermostat was stuck & finally opened up. So when I got home, I replaced it with a new 190 degree stat but the problem continues. There are no visible leaks and the coolant stays filled to the brim. During the engine install and later during my process of elimination, pretty much all the cooling components have been replaced - thermostat, hoses, water pump, fan clutch, radiator cap. The radiator itself is an unknown to me since it was replaced by the installer with a boxy aluminum one after he found an un-repairable hole in my original. He also found cracks in the exhaust manifold and replaced it with a header but since it runs so close to the engine, I'm wondering if that might be contributing to the overheating. So I'm hoping some of you might have ideas before I try a new radiator (closer to original style), sending unit & gauge to round out the possible component replacements. Also, does anyone know what actual temperatures the marks on my original FJ gauge correspond to?

Thanks in advance for any help you can offer!

 

[FJnewlife]

Based on everyone's responses, my next steps will be to...

1. Use the infrared gun to verify post-warmup temp is over 190 degrees to know that the t-stat should be open. I still may not see water flow if the blockage is somewhere else but I'll have confidence that the t-stat should be OK since it's the second new one since the engine was re-installed. Someone mentioned the rubber O-ring above the t-stat and I did install the thicker one (no sealant based on t-stat threads I'd read) and as best I can tell, it snugged up tight but I'm not sure how to verify it's not jostling around.

2. Pull the lower hose off the radiator (this aluminum one doesn't have a drain cock) and run a garden hose through the top to verify flow out the bottom. If it looks iffy, I may try to flush or take it to a radiator shop for a more detailed checkout. Worst case, I'll replace the radiator but I won't do that before doing the next step...

3. I'm really thinking I have blocked water jackets like Billinator's post who mentioned a similar sat-for-years issue. This seems to fit my situation pretty well and explains various things I'm seeing and not seeing like why it overheats only with a higher outside air temp. When it's cooler outside, the block cools down enough by the colder outside air even though it doesn't have good water flow and the inside heater will be on which would help too. So I'll do a flush of everything as best I can and see what shakes out. If memory serves, when my engine was pulled so many years ago, it went straight to the back of the garage (new pic) and sat there without the remaining water being drained (my bad). So it seems logical that the block water evaporated over time and left gunk & rust across some water jackets. I mentioned the long sit to the rebuilder but I'm guessing he did his usual block boil and like someone said, he didn't check the water jackets very closely before putting it all back together.

Mike, I like the idea of the Gano filter and the extended air cleaner hose and I'll be doing those too. Bobby didn't do the engine rebuild but he did do the re-install into the FJ and during his initial startup checkout, he discovered the rebuilder had installed the head gasket backward and fixed it. He also did the head re-work after that serious overheat later.

Thanks again everyone, your comments are very much appreciated!! I'll re-post later when I hope to have some good news to share.