I have a 1987 4Runner SR5 with the 22re engine. The factory temp gauge will creep up to the 3/4 mark on uphill grades in warm ambient temps (90+ degrees). The engine was rebuilt and the cooling system remained stock. Before the rebuild the gauge never moved past the halfway mark.


Context:

2 years ago we rebuilt a junkyard 22re engine from a 1989 2wd auto pickup. We used the 1989 block, crank, rods, head, camshaft and intake manifold. We used the 87 accessories, exhaust manifold and oil pan.

The block was bored 0.030 over and decked, and the head was rebuilt. There were no performance mods done.

During the break in, there was an issue with leaky fuel injector/s which was found through poor fuel mileage. We realized we used bad injectors and rebuilt the originals, which fixed the problem. The engine burns oil and it gets dirty fast. Not the cause of overheating but adding context.

The cooling system is stock. New aisin water pump during the rebuild. I had previously replaced the radiator with an all brass csf stock replacement radiator. Shroud is present.

I read the fan clutch fluid could cause overheating. During the rebuild we installed a new aisin fan clutch. I changed the fan clutch fluid to a thicker fluid, but that did not fix the problem.

I also read the radiator hoses can compress and cause overheating. I replaced the hoses when I replaced the radiator on the original engine and never had an overheating issue even on hot days.

The factory temp gauge has always acted funny since I bought the 4Runner 7 years ago. On a cold start it immediately goes to the halfway mark. Very rarely does it stay low and move slowly up to temp like a normal gauge. So it is strange that is is able to read hot.

Any thoughts? Could the over bore cause the engine to run hot? It would probably be a good idea to get an aftermarket temp gauge. But I want to use the original.

I also need to check what thermostat was installed during the rebuild. We used a Toyota oem one.I’m thinking of buying a new oem one and new hoses..

 

Ambient Air temperature ??

Is this at idle or after driving ?

What all has been done to the vehicle .?

Keeping up with Coolant Changes ??

coolant level correct ?

Radiator or Fan Clutch no longer working like it should.

Radiator blocked with dirt on the outside.

It can be so many different things work through one at a time.

 

not according to the gauge

 

Is the gauge actually reading the temperature of the truck? An inexpensive IR thermometer from HF, pointed at the thermostat housing may tell the tale. If the gauge isn't accurate, is it the actual gauge, or the sensor?
Is this during the warm up period? IE: Does it go high like that while the truck is warming up, then down again? Or once it stabilizes?

Personally, I would go with the fan clutch to start out. Test it IAW (In Accordance With) the FSM. It's actually easy to check. Heck, at worst, just LISTEN to the fan. Does it make a whooshing sound, and blow a LOT of air out behind the fan, when you first start if for a few, say 30 to 60, seconds? If so, once the engine warms up that far, does it start making the whooshing sound, and blowing a LOT of air, again? Until the engine cools down?
If not, it could be a lack of air flow through the radiator, OR the fan clutch being bad. Are you certain the fan is on the right way round? If it's mounted with the wrong side facing the radiator, it could be doing this by blowing the wrong direction. You laugh, it can happen. <Ahem>

Is the fan shroud on the radiator correctly, including the small stirp across the bottom? It matters. Even the small strip being missing can cause this.

Second, I would definitely look into the radiator. Literally. Take the cap off and LOOK. Are the down tubes clear, or has scale/rust/etc clogged them all up?
Same for the outside of the radiator. Is it clogged with dirt, bugs, etc? A quick blast of water from back to front from a garden hose will usually clean that out pretty well.

Is the coolant in good shape? Clean and clear, other than the color? Is it the Toyota Red coolant, or the cheapo generic green stuff? is it a 50/50 mix with distilled water, or did they use garden hose water? Have you tried a good flush of the cooling system, like with a commercially available flush?
Has the cooling system been correctly burped the least time the coolant was changed?

Just what I can think of real quick...
Pat☺

 

Thank you all for the replies. I originally added some text but the font was black so it didn't show up.

The coolant was replaced with the new engine (Aisin red). The radiator is in great shape absolutely no rust inside.

I drained the factory Aisin fan clutch fluid per a great write up on ih8mud and added 10k silicon fluid. In fact it is too thick, it sounds like the fan clutch is engaged on cold start now and is really hard to spin the fan by hand when cold.

What is the bottom foam piece on the radiator shroud? I never had a bottom piece below the shroud. Again the gauge never did this with the original engine.

I need to buy an IR temp gauge and drive it to see what the IR reads.

 

That's normal, and correct. It should, when starting it cold, seem like the fan is fully engaged, and blow a lot of air for a while. Maybe a minute, maybe a bit more. Then, it should quiet down, and blow less air. This is the normal operational method of the fan clutch.

A foam strip...across the whole bottom of the fan shroud, side to side of the radiator, or just a small one around the bottom of the small bottom strip of the fan shroud? If it's side to side of the radiator, it's a strip to block the air from going going through where it's not supposed to. It keeps the max air blowing through the radiator and AC condenser. If it's just on the small removable strip on the bottom of the fan shroud, it's there to keep the fan blades from impacting the fan shroud, and damaging the blade ends. Could you perhaps be a little more precise in the description of it, or maybe post a picture? As the saying goes, a picture is worth a thousand words...

Hope this a little help...
​​​​​​​Pat☺