Hi!

I own a Toyota Prado equipped with a 3.4 5VZ-FE engine. Some months ago the engine started to overheat sometimes (for example, when driving on highway at 60 - 70 mph). The car has 33' simex tyres.

I started by changing the thermostat and radiator cap with OEM parts. Also, the radiator is new and clean. Sadly, nothing changed.

Then I changed the fan clutch with a new FCT-013 Aisin part. Again, nothing changed.

After that, I changed the water pump with Aisin part. Now the car doesn't overheat on highway, but it started again to overheat when driving slowly on serpentines on a mountain road.

My feeling is that the fan clutch doesn't work the way it should work. After the engine overheats, the fan doesn't seem to spin faster. Do you have any idea about a test procedure?

Also, the oil and the coolant are looking clean and they don't seem to be mixed together. I never reached the red part of the indicator.

Do you have any other ideas? Thanks!

 

Hi there, try this to check the fan clutch.Do the following by hand with the engine off.
Also, do you have the fan shroud installed?

Engine cold: Fan should spin with difficulty, fan roars at start up

Engine warm: Fan spins freely by hand

Engine hot: Fan will not spin and fan roars as idle is increased

 

By engine warm, you mean the normal running temperature and by engine hot above normal running temperature?

With both engine cold and warm, it works as you described.
With the engine hot, in my opinion it should roar like when I start the car in order to keep the engine at normal temperature, but it looked like rotating with slow speed.

 

I don't think there's a definitive test.
The warm test is tricky. I would guess shortly after reaching normal operating temperature would be "warm"
Hot would be after going slow in traffic or after climbing a hill.
The fan should be very, very hard to turn if the engine is past normal operating temperature.

Are you sure the gauge is correct?

 

If the fan isn't hard to turn when the engine is hot, and doesn't roar, or whoosh, to me, that yells fan clutch. I've gone through more fan clutches than I can count, when I lived in Yuma. That place is hard on cooling systems.

It's an inexpensive part, and easy to replace. Even if it's good, you've got a "known good" spare now. If it's not, problem solved.

The fan shroud is important, too. It must be in place, including the small strip across the bottom of it.

It's a good idea to get a remot kind of thermometer, and verify the gauge is functioning correctly. Read at the thermostat housing, and compare to the gauge. They are known for their errors. Like reading 1/4 deflection with the engine warm. Should really be about 1/2. If/when it shows and overheat, check it with the remote thermometer. That will tell the tale.

Don't forget, as well, the single-stage thermostats are known to allow the cooling system to go pretty far up before they pop. It's just the way the system is designed. That's why Toyota came out with the two-stage thermostat. If the system goes up to about 3/4 or a bit more, then drops off again, it's just a single-stage thermostat.

Last, make sure you burp the system well after doing any kind of work on it. These systems are known for trapping air in them, making the truck run hot. Very important to burp it.

Good luck!
Pat☺

 

Thanks all for replies!

I managed to warm up the engine up to near the red point and the fan gets a bit harder to spin, but, in my opinion, still very easy. It doesn't need too much force. But.. the clutch is new and it is Aisin.

I am pretty sure the gauge is correct because, when it shows a high temperature, the hose between the engine and the radiator is harder and a bit inflated.

I double checked the system and it looks like well burped.

What brand for fan clutch do you recommend?

 

Aisin for the fan clutch.

 

Well.. then I will still investigate. Hopefully there is not a small crack in the head gasket.

 

If you're worried about a HG (and it's not bed enough to be obvious yet):
1) Pull the plugs and look for any that are noticeably cleaner than the others
2) Test the cooling system for combustion gasses: https://www.autozone.com/test-scan-a...tor/391378_0_0

 

If the gauge is showing near the red line, but the fan clutch isn't engaging, it could be the radiator, believe it or not. If the radiator isn't exchanging the heat out to the air, the fan clutch doesn't get hot enough to engage.

Have you looked into the radiator with the engine running? When it's warm, do you have good flow through the radiator?
Have you looked at the down-tubes you can see, and are they clear, or clogged up?
Is the air coming out of the rear face of the fan hot, ie HOT, or is it much cooler than it should be? If it's good and hot, but the fan clutch isn't engaging, bad clutch, new or not. Mass production isn't perfect. You do get bad parts.
Is the outflow hose of the radiator HOT, or much cooler than the top, inflow hose?

If you have low flow rate through the radiator, it could e the water pump. If any of the rest is true, bad radiator. Something to look at before you go replacing a perfectly good Head Gasket.

Good luck!
Pat☺

 

Just to let you all know:

After changing (in this order):
​​- radiator (new NRF radiator)
- thermostat (toyota OE)
- radiator cap (toyota OE)
- fan clutch (new Aisin part)
- water pump (new Aisin part)
my 3.4 5VZ-FE was still overheating.. the oil and the cooling fluid were perfectly clean.

Well.. I discovered that the input and the output of the radiator were both at the same temperature, very hot. So, I tried again with the radiator and I discovered that my new NRF radiator was defective/clogged even if it was a new, unused part, bought from an international car parts store.

Thanks all for help

 

I'm glad you got it figured out! Thanks for letting us know what it was. The joys of mass production,

Now, there's one more step, required of 4Runner owners: Go out and thoroughly enjoy driving your truck!
Pat☺