Fixed...

***Fixed:

after flushing the radiator/engine block it has not overheated. I think fin material from the old water pump was clogging the system.

 

Maybe the fan clutch is out? But that wouldn't explain the overheating on the freeway...that amount of airflow would make up for the fan not working.

Was the thermostat installed correctly? I've read that if it's installed upside down it will cause overheating and it's a fairly common issue.

Which year truck/engine are we talking about here?

 

96 tacoma 3rz... I wasn't aware there was such a thing as "upside down" in a thermostat, just backwards. (april fools?) this thing is going to be sitting in the driveway while I ride the motorcycle to work... may be going for parts at this point.

 

What brand pump and tstat? Have you pulled the fan clutch and added fluid yet? You can also adjust it to "turn on" sooner, by tweaking the set screws and/or the coil spring.

I just replaced a near new pump and tstat on a Tundra that was experiencing low rpm overheating. The other shop put cheap motorad tstat and a no name pump on it. Swapped it out with aisin and no more overheating. The build quality on the aisin tstat was extremely better.

 

No idea what pump or thermostat... at this point I'm up for trying anything as there are no reliable shops or mechanics here so it's fix it myself or scrap it. How can I set the fan to have no clutch, fully engaged all of the time? Wasn't aware there was such a thing as fan clutch fluid.

I just tried turning the fan while the engine is off and it turns very easily in my fingers... is that normal?

 

maybe your heat core is clogged internally being that old someone may have put some other non compatible coolant in there and it clogged. I wouldnt run 100% antifreeze needs to be mix 50/50.

 

radiator cores? or do you mean the actual heater loop? I didn't grow up wrenching on stuff so as far as I know it's just hoses, head, pump radiator that the fluid passes through...

 

Please share more. I've never seen one that was serviceable as you are describing.

Then again I've not had a vehicle with a mechanical variable fan clutch in a long time either.

IIRC isn't the purpose of the fan clutch to have it disengage when higher RPMs are reached, under the assumption that vehicle speed will be creating air flow across the radiator? And it engages at low RPM to provide mechanical cooling?

 

Heater core. In the cab. It's what the heater hoses hook to. Like a baby radiator to warm your body.

When you leave the radiator cap off and allow the truck to idle up to operating temp, do you visually see coolant flow? It has to be hot enough for the tstat to open for that to happen.

 

its under your dash but I know fluid goes through it. does it have electric fans at all? or just straight clutch fan? could be a bad thermostat out of the box...not usual but could happen...

 

Every toyota one I have come across, is serviceable in as much as you can swap out the fluid to get the lockup speed to change. And many models have the temp set screws. If there is no temp set screws, then you take your needle nose and grab the spring where it mounts to the plate(not valve) and bend it counter clockwise. That will make it come on a little earlier.

I just use a heatgun and IR reader, but in this writeup he uses an oven. And instead of Toy fluid we use RC diff fluid.

https://forum.ih8mud.com/threads/blue-fan-clutch-mod.102633/

https://forum.ih8mud.com/threads/fan-clutch-service.167678/

 

This, water is better at dissipating heat than antifreeze. Some people who drive their cars hard or race in a climate that stays warm all year will run straight water and an anti corrosive additive like '

$14 Red Line (80204) Water Wetter - Coolant Additives - 12 oz Bottle

water wetter'.

 

If you are using straight antifreeze DONT because it needs water to make it function properly and it will overheat, you would be better served by using the correct pre mix for your year and engine type
TOMB

 

Didn't know that. Didn't realize it doesn't have as good a heat conducting property. I'll try running 50/50 with distilled water, see what happens. Weird that it's been overheating easier as time passes. I think it's got some gasket/head problems on top of whatever else is going on (antifreeze etc...)

 

Not that i need to because so many have already pointed this out. But I will anyway. NEVER run pure anti-freeze for any reason. Always a 50/50 mix.

 

check your oil, make sure it looks normal not milky foamy etc.

 

I changed it out of curiosity. Not milky or foamy... but since I was running straight antifreeze who knows... hehe... I just went to 50/50 distilled water at this point. Still overheating on the highway but when I revv the hell out of it at slow speeds (like off-road) it is not. After four wheeling for about 20 minutes the other night my exhaust header was cherry red, but the coolant temperature wasn't reading high, and the radiator wasn't boiling... so at this point no idea.

 

that is odd, maybe fan or temp sensor problems..

 

not sure... you'd think the airflow at 80 mph would be enough that the fan wouldn't matter but it's overheating on highway in straight lines most of all...Been checking the radiator and hose temps with a temp gun and it seems like the sensor is working.

at this point for a 21 year old truck with no AC with everything replaced that I have the time to fix myself I'm moving on... I may have to commute 400 miles a week soon and don't have time to mess with it anymore. Probably selling it as-is with the stipulation that it's for parts. This is the time where if I had a buddy with a shop I'd throw him a gun or some cash to work on it but don't have that anymore.

 

yeah Ive done that in the past on vehicles for similar reasons...I needed something dependable, no time to mess with it, no place to mess with and short on funds.