Overheating, need help diagnosing. 22r
 

Searched as much as I could to try and find a solution. Guess I need to ask for help. The other day my truck ('87 4x4 22r 5 speed manual) started overheating on the highway. Recently had a mechanic install a weber 36. When I drove slower at lower rpm the temperature would go down. Checked fluids. Oil is good. Antifreeze is good. Last night it overheated thru the roof and didn't cool as I went to lower rpm. Pulled the thermostat out. Still overheated. Replaced the thermostat, still overheated. Not showing any leaking in the cab. Ran a hose to bypass the heater core, still overheated. Not showing any sign of leaking anywhere. Fan belt spins the fan and water pump. All hoses get warm except the lower radiator hose. After letting the car sit for an hour after starting it up, shortly after as it starts to warm up it heats up through the roof. It doesn't make sense to me how can my engine be overheating from a cold start in less that a few minutes?

It doesn't take long for IC engines to get hotted up, especially with no water circulation. They generate a ton of waste heat. 5 minutes is a very reasonable time to go from cold to overheated.

The cold lower radiator hose is a major clue. May be clogged up radiator down tubes, the water pump/alternator belt, OR the water pump. Sure sounds like the water pump or the belt to me.
Easy to check the belt, after all. Just LOOK at it. It's the one nearest the engine. A good clue is the CHARGE and PARK BRAKE lights both on.
If you pull the radiator cap, and there's no water circulating, probably the water pump. Another way to check is to feel, when the left side of the top tank on the radiator gets hot, does the right side? If not, water pump. Be very cautious, it gets HOT!
If it looks like water is trying to circulate, but the lower hose stays cold, radiator is clogged up. Some shops will pull the tanks and rod the cores out for you, but at the price, may as well buy a new radiator.
Personally, I would get an all-metal, 3 core radiator. Rock Auto sells CSF all-metal 3 cores, IIRC. Or ask at you local shops. I put one in my pickup when I lived in Yuma, shortly after I bought it. Dropped right in, and is STILL working good, maybe 30 years later.

Check the oil cap for a substance that looks like a chocolate milkshake. Very often, when you get an overheat condition, the head gasket fails. And/or the head cracks. Since you got a bad overheat, I would pull the head off and send it to a good, reliable, machine shop to get tested for cracks, and for warpage. Chances are good it will need replacement. Regardless, if you pull the head, new head gasket.
No matter what, I'm pretty sure you're going to need a new head gasket. Overheats do that.

BTW, it would help us to know the year, model, and engine model of your truck. Like 1987 4Runner, 22RE, 5 SPD Manual. The more information you can provide will help us help you better. That's why so many people in these forums put all that in their signature lines. That way we know right off what we're talking about, and can get on the same page.

Good luck, and let us know what you find!
Pat☺

Thanks. Sorry not familiar with how to use this site. I thought that my vehicle description showed from my profile. It's an '87 4x4 5 speed manual 22r. The oil looks good. The fan/pump belt is turning fine. Not sure how I check if water is trying to circulate. I'll do some research and try to figure out how to pull the rods is it? I prefer to do work on my truck myself to ensure things are done efficiently and mostly to save a buck. Thanks a bunch for the reply.

Ya, this doesn't make sense that within two minutes of starting the truck the temperature guage says its 100% overheated. The needle is thru the roof. But the only thing warm in the engine is the exhaust manifold and that still isn't over 100 degrees at that point. I can hold on to it. If anyone has any advice please tell me. I've been reading up as much as I can find and calling mechanics left and right trying to find a solution that I can solve myself. What I've read about the fan clutch is confusing, saying that it should spin with resistance and only be able to spin several revolutions. Is has no resistance while cold and I can't allow my engine to overheat at this point or warm up but after running for a few minutes there is a little bit more resistance. But it doesn't increase the more I spin it. It just keeps spinning. I read on this site that I should be able to stop the fan with my hands on a cold start which seems ridiculously crazy. Never the less I did try to stop it with a screwdriver but that didn't go well 🙄. And even still if it's the fan clutch I would imagine that it would take some time before it overheats for that to be the issue. Most problems I've experienced with overheating the vehicle is able to be driven several miles before overheating and then able to be let sit for half an hour to be driven a fee miles again. I am unable to let the truck even get a chance to warm up before it says it's overheating. I know there is a problem and it's not just the gauge because the othe night when the guage first went through the roof I could tell it was overheated from visual inspection. I could feel the heat in the flooring through the firewall. Maybe now the guage is also broken? Any advice would be helpful. Thanks.

IF New Radiator Deemed Necessary...
 

Before you fix any problem, you need to verify that it really exists. buy your own non-contact thermometer or borrow from friendly A/C guy.
https://cimg3.ibsrv.net/gimg/www.yot...31c4c9ef60.png

I found out my temp sender was the reasons for my high-temp reading.
https://cimg5.ibsrv.net/gimg/www.yot...121ea79a6b.jpg
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Actual experience with CSF 2306 and CSF 2314 Radiators:
https://www.yotatech.com/forums/f199...l#post52474363

Original problem solved. Fan clutch had went out and caused the overheating. I believe while checking the thermostat there was liquid and dirt or oil that flushed into the connections of the coolant temperature sensor and caused it to malfunction. After unplugging and cleaning the connections and reconnecting the sensor the problem of the instant overheating went away. Thanks for the help and advice.

Cool!
Appreciate you sharing what fixed you issue for others to learn from.