Motorheadno13

Relevant Specs: 94 4Runner, 3VZE w/ maybe 50k? 3 row brass/copper radiator, Thorley headers into 2 1/2catback, custom intake, tuned with a fuel manager, timing set at 10degrees advance, 275/85/16 mud terrain km2's, geared with 4.88's.

The I-15 in California and Nevada has a bunch of climbs that last for miles. They don't have a really steep grade, but are still long and steep enough for semi's and slow vehicles to ride in a dedicated lane. Some of the climbs only have a subtle angle with no dedicated lane, but can reach over 10miles.

Climbing these hills cause my truck's temperature climb until it overheats, unless I slow down enough to take any sort of load of the engine. Then it stabilizes at the current temp, or cools off a little. It doesn't matter how steep the hills are. If they are long enough, the truck will overheat within 2minutes of loading the engine. The temperature outside also doesn't take part in this. However, running the A/C in almost any situation will cause the temp to rise as well.

Temps are very stable when driving around the city, or even shooting up the I-5 to LA from San Diego. It's only when there is a constant load or the a/c is running, which obviously puts a constant load on the engine...

Here's what I've diagnosed so far. Running the heat on full blast will cause the temp to drop a bit. There are no symptoms of a bad water pump that I've noticed. No head gasket symptoms, tested radiator flow (good), new thermostat, flushed and burped system, new fan clutch.

I don't know what else I'm missing. There are a few thoughts going through my head like, beef up the cooling system.. but it doesn't make sense to me. From what I've found, the radiator is more than capable enough for that engine. I've also thought about Toyota's design on the heads, and how they don't flow very well, or if there could be a blockage somewhere else in the system. But if there was a blockage somewhere else, wouldn't it overheat all the time?

I'll update the thread with any changes. Thanks for reading...

Marc

Do you have the fan shroud on?

MaK92-4RnR

Fan clutch.

Motorheadno13

Yes the OE fan shroud is there.

I replaced the fan clutch already (pepboys replacement). I've heard they are no good, but it seems to be working fine. The clutch kicks on during engine starts then disengages after a minute or so. I hear it periodically engaging when around the city, but never on the freeway. I can't recall if it engaged during the climbs or when I slowed down. I'm assuming it should engage when the A/C is on as well. The system is drained at the moment so I'll fill it today or tomorrow and give it a go.

snobdds

Pressure test the system. Testers can be rented from autozone for use. See if there is any areas where there may be a leak. Also, test the radiator cap to make sure it hold around 13psi.

However, it sounds like a bad radiator, even though you say it flows ok. There is really no test that you can do, while the radiator is on the truck, to make sure your radiator is ok. Half of it may be flowing good, while the other half is cloged, but it seems like its ok.

Motorheadno13

Will do, thanks for the suggestions. I suppose it could still be the radiator. To give you an idea of how we tested it; it was back flushed, then I covered the bottom outlet with my hand, filled the radiator and I released the water and watched it drain in about 2 seconds. Cap is newer as well, but it won't hurt to test it with the rest of the system.

Marc

Get an IR temp gun. They're cheap these days.
Aim it at different places on the rad to see if it's flowing well.

Motorheadno13

I tested the cooling system earlier today. Everything looked good. First I pressurized the system up to 15psi with the engine cold. It held well, the dropped about a 1/2psi after about 2 minutes. I'm assuming that's normal, but I've never done this sort of test before.

Next I released the pressure and started the engine, making sure a pressure spike didn't occur from a leaky cylinder. I know this was redundant since it would have lost pressure on the previous test, but I did it anyway.. The pressure slowly rose and stabilized around 5-6psi, as the engine warmed before I shut it off.

I couldn't find an adapter to test the radiator cap, but it is a 13psi cap and about 2 years old. I don't think its the problem. Still not positive though, so I'll check it out this week.

An IR temp gun? Engine warmed up, but on or off? If on, how would I get an accurate reading with the fan pulling and in the way?

Thanks for all the input...

Marc

Take the readings with the engine running and hot.

The fan shouldn't be a problem if you take the readings through the front grill.

Dingotech

Is this an auto? I had a 94 4Runner, 3VZE, auto and that sucker would periodically over heat during long highway drives. I'd stop, open the hood for 10 minutes and then resume driving. I was told that this was not uncommon in autos.

Motorheadno13

I suppose it will still get a decent reading through the condensor. I'll give it a shot.

Also, the truck is a manual. I wonder why the autos overheat? Does the cooling system also supply the tranny?

Marc

Sorry, forgot you had A/C. It will be tough with the condensor.

I don't think auto's have overheating issues as a rule.

Motorheadno13

Well I took an IR temp gun to the radiator today. I kept the engine running and stopped the fan with a rag. Then tried my best to hit the whole engine side of the radiator. The fan was def in the way of some areas but I managed to find 205-6f in one area while 190's in the areas, closer to top tank.

I also ran the gun across the bottom front side of the radiator. About 2 inches of radiator was showing where the condenser ends. The gun was showing around 104f across the board.

I'm not sure if these readings say one of the rows in the core might be clogged, or a section of a row, or that the temps are normal given the engine side would naturally be hotter..