2000 3RZFE Cooling Issue

Okay guys. First thread creation on TW. I need some assistance with my freshly rebuilt 3RZFE. Note timeline as I travel a lot for work.

Background: I have a 2000 Tacoma that had a cracked cylinder head between #2 and #3 cylinders on exhaust valve side. After pulling the motor to go ahead and replace the timing system and water pump, I decided to just go ahead and do a full rebuilt since I had the block out and it had 197,710 miles on it at that time. Motor was completely rebuilt (block was decked and bores were within spec so honed only -> engine machine shop performed the deck and hone). Crank was polished and new OEM bearings were added, new pistons & rings, etc. (complete rebuild). Cranked truck up in October 2015 and oil pump broke after 10 seconds or so ( Post #18 -> https://www.tacomaworld.com/threads/help-oil-pressure-issue.417750/#post-11899242). With advice from BamaToy1997 I pulled the motor, tore it down and flushed the entire block and head to get any metal shavings out (including oil pan and coolant hoses), honed the cylinders again. Late Feb I got it completely rebuilt, again, and fired it up. Ran fine but the temp is a bit hotter than I expected it to get but wasn't too surprised since it has basically brand new parts everywhere and they will need time to break in together.

Problem is the cooling system: Truck will idle for 25 to 30 minutes before the temp climbs higher than the normal OEM gauge has always shown. If I give it gas it will obviously climb much higher while sitting in my shop. I have about 20 miles on the new motor and while driving 55 to 60 mph it still runs increasingly hot (not overheating, but very hot). I haven't pressed it further once the temp gets close to the OEM gauge red line, for fear of damaging the HG, etc.



Troubleshooting steps to date:
1. New coolant hoses everywhere (reinforced silicone).
2. Radiator has only 10k miles on it since the factory one cracked on the top plastic section long before the CH cracked.
3. New Radiator cap and T-Stat (Stant and Toyota OEM have been used)
4. New Water Pump
5. Heater core was flushed during rebuild while the block was out both times
6. April 6th, 2016 -> Combustion Gas Leak Test (Block Tester) was performed and showed no exhaust gas in the coolant system (motor does not smoke out the exhaust pipe either).
7. No leaks are detected anywhere (outside the block).
8. Oil was changed and looked fine with the correct consistency (obviously looked brand new as it only had 20 miles and about 1.5 hours run time on it).

I'm at a loss for what to check now. I have checked for collapsing hoses everywhere, coolant flow looks fine inside the radiator with the cap off. System was burped multiple times to ensure air was out of the system. I ordered a real temp gauge to see what is actually going on with the temp and will install this weekend. Any thoughts as to what else to check? The only test I haven't done is a pressure test and I will look into doing that as well.

Considering the following, post real temp gauge installation: Replacing the silicone hoses with traditional rubber reinforced hoses from the radiator to the block (input and output sides). If the hose change causes no change in temp, then changing the water pump back to the factory pump (temporarily) to see if the new pump I have isn't working properly. Again, that is all secondary to putting the real gauge in. It may be the stupid factory temp gauge that is causing the grief.

 

I'm assuming the cracked had was replaced? I may have skimmed over that but didn't see that you had. I'd put a scanner on it and see what the computer says the temp is. It very well could be a gauge or sensor issue. Only other thing I'd know to check is make sure the fan clutch is working as it should. However driving down the road there should be enough air flow to keep it cool.

 

Cylinder head is brand new (not a reman) and was checked at the machine shop for warpage/cracks when I dropped the block off. I was originally just going to change the Head and gasket/timing, etc. but I decided to pull the motor instead of dropping the differential to change the timing chains.

I am in no way an expert, but it is my understanding that the fan clutch is only utilized at low or no speed. Once you are driving over 20-25mph, the fan clutch is essentially free spinning as the force of air through the radiator is from driving instead of pulling air with the fan.

 

Essentially that's all it's there for, just to cool during low/no speed situations.

 

I had the same issue with a new radiator cap and replaced it again and my problem went away.

Drove me crazy for two months.