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1991 Toyota Pickup - Overheats

I have a 1991 Toyota Pickup Winnebago Warrior with the 3VZE 6 cylinder… I think I know a solution to my issue, but want to hear your thoughts please!

While I am sitting still or slowly moving in warm weather, the engine heats up to redline - I can shut down the a/c and put on the heat to cool it off.
I am aware that this engine has a tiny radiator, blocked by a transmission cooler and A/C cooler.
So if I am in stop and go or lots of stop lights, I have to keep the A/C off and windows down in the heat, when I need the A/C on the most…
I have replaced all belts, fan clutch, flushed radiator, timing, water pump, etc myself.
I can think of only one other remedy as I think this may be a design issue and not something wrong, but want to see if you have other options, opinions, or come up with the same idea I have.

Thank you!!!

On a thirty year old vehicle, you may need a new radiator. Flushing often will not be adequate to clear blocked tubes full of rust and scale.


Maybe there is a buildup of bugs and debris on the ac coil.

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Can I conclude that there is no overheating problem once the truck is up to speed? As @Barkydog suggested there may be an accumulation of debris in the condenser and also the radiator that the fan cannot overcome. If the radiator were internally plugged the overheating would be worse at highway speed in warm weather.

How long have you owned the truck? If the truck is new to you how do you know the problem has been around since mile one? And if so adding an electric fan at the front of the condenser to boost the air flow when needed might be necessary. If you are desperately needing the AC in March you’re in a hot region and an additional fan is often needed in extreme heat. And the dual evaporator AC does add a great deal more heat to be dealt with by the cooling system.


The first thing I would do is use this


any decent auto parts store will have this in stock, and it’s not very expensive

This sounds like it had a weak cooling system when new. Now anything could cause overheating. I’d check if an aftermarket higher capacity radiator is available. The same for the fan. I had to do both to keep from running my Duster’s heater in Houston in the summer.


So I just wanted other opinions - I believe the cooling system is just weak - the radiator is in perfect condition, clean, unclogged, and rust free. In front of this radiator is the AC cooler and transmission cooler, so it gets water hot air they produce in front of it.
The Toyota Pickup Winnebago was built on the standard Toyota pickup so it’s already working hard to carry the load. I just wanted other opinions without prompting my theory to make sure it wasn’t something I didn’t think of.

My idea was to add a cooler fan with a switch in the cab to turn on when in traffic.

Has anyone done this?

Yes it cools at speed… it only does this mostly when the AC is on and slow or stopped.
I’ve owned it for about a year now, live in Florida, and it spent its previous life in Minnesota, where they may have never faced this heat issue… I think the extra fan is my answer, but want to make sure before I did it.

Did this problem begin suddenly? If so, any work done on the vehicle just prior to that? Is the radiator fan driven by the engine via a drive belt, or an electric motor?

I’m presuming you’ve replaced the thermostat already and it’s installed w/the correct orientation, all air is removed from the cooling system, idle rpm, idle ignition timing, & idle mixture are correct, water pump volume flow meets spec, radiator cap regulates the cooling pressure to spec, belts aren’t slipping, and you aren’t losing any coolant. hmmm … well, could be a problematic head gasket or cracked block. Do you notice any bubbles coming up through the radiator as the engine warm idles?

I’m thinking however there’s some sort of problem with the airflow through the radiator at idle. The idle airflow is due entirely to the engine compartment fan. If a visual inspection at warm idle shows the fan turning robustly and no other obvious problems like broken blades etc, the next step is to verify the fan is actually turning at the correct rpm when the engine is idling. Ask your shop if they have a way to measure the fan rpm. If they have a variable-frequency-strobe light , it might be possible to measure the fan rpm that way.

Have you looked for a forum for this RV? I bet others have solved this problem.

I have looked in forums and some people have had the same issue, but I haven’t found an overwhelming amount and those people didn’t have much answers… most just turned off the AC…

I had this problem 15 minutes after I bought it… the previous owner said he hadn’t had any issue and paid for a radiator flush, thermostat, and new fan clutch.

When I got home I got home - 2 days and few thousand miles later (this is a Toyota, so it just keeps on keeping on) I did the belts, water pump, etc… everything I could think of. Still, if it’s hot outside and I run the AC while slow or stopped, it redlines… I think the fan is the answer, so I am going to install one, but I appreciate all the other thoughts - a few I hadn’t come up with!

Also, no cracks or leaks… runs like a top. Small exhaust leak tick, but that’s all.

I am my shop too… I do all the work myself via YouTube unless it’s too big and then my buddy who is a mechanic does stuff with me. I know he has a timing gun if that’s what you are referring to for the fan?

Right now the RV is in a lot in Vegas so I can fly out with my kids to do some national parks… just going to have to do the fan on the radiator at a campsite or something :roll_eyes: I think it is just the air flow

I gave you good advice

Why will you not consider buying that tool I mentioned . . . ?!

Since he didn’t mention bubbles in the coolant, or loss of coolant, I do not think this is a head gasket problem. I have purchased enough very old used cars to know that unless the coolant was changed regularly (which most people fail to do), there will be visible sludge inside the radiator and expansion tank.

I also understand the fact that with a modern micro-channel type radiator, no amount of flushing will clean it out internally. Even if many rows are plugged with sludge, you can put a garden hose on the inlet or outlet, and water will come out the other side. However, the radiator might have severely reduced cooling capacity compared to a new one.

Since these Toyota truck-cab based campers and RV’s use the same mechanical parts as a regular Toyota pickup of the same year, aftermarket parts are readily available. A quick trip to Rock should have a new radiator and hoses from a quality brand shipped to your door for less than $150.

During a particularly hot summer years ago I added electric fans to several vehicles, most notably shuttle buses and emergency vehicles that usually ran with the AC on continuously through the day. On a large shuttle bus I actually shimmed the hood up several inches at the rear to allow the extremely hot air that accumulated under the hood to escape when idling at a stop.

A new radiator will have clean innards and its fins will be well attached to the tubes. Better heat transfer is the result. An old radiator can be subpar in both aspects, especially if it’s been exposed to salted roads.

I used to have a 1979 Toyota 4X4 and read a few catalogs and participated on some discussion websites. Some owners put electric fans on their modified off-road vehicles.

I’ve seen a few cars that didn’t have the classic symptoms of bad head gaskets . . . yet tests revealed that was in fact the root cause of the problem(s)

If this were my vehicle, I’d do that test . . . if for no other reason than to rule out a bad head head gasket, cracked block, or some other way that coolant may be getting into the combustion chamber

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While it sounds like I’m full of myself and I agree with @db4690 re testing for a head gasket leak I have never failed to detect an internal combustion chamber leak into the cooling system by smelling the hot coolant. I had a tail pipe CO-hydrocarbon tester and the chemical test set to positively verify questionable leaks before pulling off a head, etc., and the test always agreed with my sniff. But then I can smell CO.

Are you sure the gauge is reading correctly? Perhaps the sensor is flaky.