1FZ suddenly running quite hot - why?

[arulataq]

So, I seem to have solved one issue (see: https://forum.ih8mud.com/80-series-tech/509572-intermittent-starting-issue-when-hot-new-me-cruiser.html) but had another jump in to fill its place.

I drove a few hundred miles for a weekend of hunting (Bozeman, MT to Casper, WY), parking the cruiser and not starting it for 3 days. On the drive down, coolant temps fluctuated between 185-195 depending upon steepness of grade, etc. Upon starting the cruiser today to head home, my temps climbed steadily higher than this, at times reaching 231 (at which point I pulled over, opened the hood, and ran the truck at a high-idle until significantly cooler). I seemed to run in the 215-225 range most of the time, however.

Background:
- the truck has ~174k miles, seems to run well, and was purchased recently
- the previous owner performed a bunch of PM, some of which included replacing all coolant hoses (the cooling system appears to otherwise be original)
- the fan clutch appears to be original and is a bit (quite a bit?) weak
- the factory temperature gauge, my scan gauge, and the AC cut-out agree on temperature, so sensors don't appear to be the issue

Starting with the low-hanging and locally available fruit (as I pulled off in Buffalo, WY), I changed out the thermostat thinking it may have stuck closed, draining and refilling with the same coolant. This didn't help.

At CDan's urging (thanks again for the advice!) I performed the overflow tank bubble test, seeing none, and, thus, assuming the headgasket is ok.

I then stopped about 35 miles down the road in Sheridan, WY as temps were still too high for comfort and brought the truck to a Toyota dealership, having the cooling system flushed (with cleaning solutions, etc.) and refilled with a 50/50 Toyota red/water mix (the old anti-freeze boiling point was tested and it was found to be 90/10 water/Toyota red). This didn't help either.

While at the Toyota dealership I had the headgasket "tested" again, this time with the CO2-sensitive liquid test, finding that the gasket appears to be good (no color change whatsoever).

I ultimately limped the few hundred miles back to Bozeman, stopping and cooling down the engine whenever the temps approached 228-230 (never letting it go higher or staying at these temps for long).

So, assuming my results thus far are correct, I'm left with:
- a bad fan clutch
- a bad water pump
- a bad radiator
- ?

Now, I'm definitely going to replace the fan clutch, but I'm trying to determine what else, if anything, would be prudent to order from CDan to replace simultaneously.

Any thoughts? I'd love to hear what anyone would suggest as I'm really not sure how to proceed beyond the fan clutch.

 

[Flank]

I would bet dollars to doughnuts that you need two things - fan clutch help and radiator cleaning. Fan clutch can probably used some new thicker fluid (even a new fan clutch - do a search on fan clutch mod), and you can have your radiator removed, tanks pulled and get it rodded to get the 15 or so years of crap and sludge out.
My 95's rad was always well serviced, but was about 50% blocked when I got it cleaned recently. I pulled it myself, so it cost me $125 to get it rodded.

In the "while you're in there" realm - new rad hoses and clamps, check distributor for o-ring leak, and this is a great time to look after the oil pump cover and / crank seal if you have oil and grime in the front of the engine.

 

[Frankencruiser]

Maybe your new thermostat was bad? You can check it by putting it in a pan of water on your stove, slowly heat it up and it should open at about 170. Like flank said the other main candidate is the radiator. At highway speeds with a light load the fan shouldn't make much difference.

Is your radiator cap good? If it won't hold pressure it can cause overheating.

 

[BrotherRob]

I have to concur, it sounds like you are heating up under load but it is cooling down while idling at high RPMs. That usually means radiator or some other flow issue. I would consider a new radiator.

If your fan clutch is original, it could probably stand to be serviced, but I doubt that, alone, will solve your problem.

 

[95LCMachine]

First I have to say that 230 is too Hot. I would be pulling over well before that.

Do you run the heater when you see the temps start climbing?

are your belts tight? it sounds like the fan clutch is working well enough so the belts shouldnt be an issue, but some thing to check for sure.

Im guessing Rad....

 

[Wheelingnoob]

A good test that worked for me when I was having hot run on hills was. Pull over when it gets hot like 220f, turn off truck, slip hand between fan and rad to see if there is cold spots or sections of the rad. Once done start truck and let it cool.

I did this after refilling my clutch with 10cst fluid and no change turned out 80% of my rad was blocked, this was after spending $100 to get the rad cleaned at a rad shop. $550 new OEM rad later and my truck has not been over 195f since.

I also changed everything in my cooling system, all hoses and belts only thing original is the Water pump and heater core.

 

[Flank]

I did this after refilling my clutch with 10cst fluid and no change turned out 80% of my rad was blocked, this was after spending $100 to get the rad cleaned at a rad shop. $550 new OEM rad later and my truck has not been over 195f since.

Ouch - Sounds like you need a new radiator shop - they obviously did a poor job cleaning it.

 

[Wheelingnoob]

Ouch - Sounds like you need a new radiator shop - they obviously did a poor job cleaning it.

They just boiled it over, I took it back and got my money back after showing them is was 80% blocked with sludge.

I got a OEM 93 3 cor Brass replacement from Toyota.

 

[Flank]

Yeah, a proper rad shop will remove both the top and bottom tanks, completely rod and flush it out so that (if there are no leaks or weak spots) it will flow as good as new. I decided to try this prior to purchasing a new rad, and it worked great.

 

[arulataq]

Just a quick update:
Decided to do it right (mostly, anyways) while I was into the cooling system, so just ordered a thermostat, water pump, and fan clutch from Onur. Go-part is shipping out a Koyo 1917 radiator, as well, so with a little luck, we'll be good to go later in the week.