1999 SWB Pajero 3.5 overheating in desert only

[gaurav]

Hi guys, its very nice to see so many Pajero enthusiast under one roof.

I bought 99 Pajero 3.5 (SWb) 2 door with Automatic gear about 1 month back with 138k kms on clock and in good condition. I can drive this for hrs and hrs and everything is fine. When going in desert and engaging 4x4 if drive on low revs temp goes up very slightly and very slowly. But if i drive in Hi revs which i have to in sand in climbing dunes it overheat real bad that i have to exit desert immediately.

I thought due to its age radiator must be clogged, so got it all opened and cleaned all pipes in detail but no luck. Just tested today after radiator cleaning its still throwing heat.

Any leads or advises are highly appreciated. Thanks in advance.

[dragon]

are your coolant mixtures correct you may need summer coolant in the radiator and depends wot temp you drive in realy but i would also be tempted to add something like a kenlow electric fan and an adjustable temp control so you can set it to come on at a lower temp.
also wot ratio are you mixing your coolant at ?????

[dragon]

also check the viscose fan is operating properly and all belts are at correct tension

[gaurav]

Thanks dragon, for your valuable input.

Thermostat is out last week as first doubt. Regarding coolant before it was the same coolant with which i purchased (dont know the mixture ratio). After cleaning the radiator i am running on bottled drinking water as for dubai antifreeze is not imp. Once sorted with trouble ill top up with original coolant, as mitsubishi coolant is quite expensive here (8 liter = 60 USD).

I have driven many cars with clean drinking water before as a test and it shud work fine. But still i always buy coolant as its long lasting unlike water.

Dubai temp at the moment is around 40 degree centigrade (+- 2)

I chekced the viscose fan and both speed when hot and its working fine. All belts tension seems ok, but i can get it checked.

Do you think changing ATF and Engine oil might help, as may be atf is worn out and thats why not absorbing enuf heat and returning it back to the radiator (same for engine oil too).???????
(i read this in some thread and want to know people opinion if it make sense in my case)

[Trojan]

Did you test the thermostat for correct operation?

If not, take it back out and test it.

You need two water containers about big enough to fit a pint of water in.

Container #1 needs to be cold and container #2 needs to be at about 80 degrees centigrade/ 180 degrees Fahrenheit which is a common thermostat opening temperature.

Have a pair of BBQ tongues ready and you should have a thermometer to test the water temperature precisely. Put the stat in container 1 for a minute and then using the tongues, take it out and drop it in container 2 for a minute. After about 30 seconds, it should open. If it doesn't, add boiling water into container 2 to raise the temp by 5 degree C amounts to see at what temperature the stat does open. If it's about 90-95 degrees C, that's at the upper limit, but okay. If it opens at 96 degrees C or above, you've got a duff stat and it's holding water back against the engine jacket for too long.

Given the local ambient temperature you're working in, I'd change the engine oil, ATF and the transfer oil case as a matter of course and probably the front and rear diff's on a regular basis, say 5000km anyway. ATF under normal conditions should be replaced at about 8000km in a higher mileage autobox just to preserve the life of the torque converter and engine oil acts as a coolant as well as a lubricant and I change mine every 8000km when I do the ATF.

Ya can't beat a good maintenance routine for heading off problems.

[gaurav]

Thanks trojan for all this. Looks like you have set some radar and satellite in Dubai over me.

I removed thermostat long back, and yes it was new and working. Yesterday about same time when u post this message i was getting gear oil, gasket and filter and Engine oil and oil filter changed. As i was doubting this quite a lot, so thought of getting normal maintenence wont hurt. I use the fully synthetic engine and original mitsubishi SPF III ATF for gear.

Car runs and shift lot better now, will be testing in desert soon.

Will also get all diff oil change soon, thats a good tip.

In next text i will spare carry radiator cap from my friend pajero and if it still overheat i will change the cap and see, as one of the mechanic doubt it could be rad cap.

[dragon]

could also be an air lock in the cooling system.
jack the front end of your paj as high as you can
put all your heaters front and rear on hot as they will go and full blow and with rad cap off run for about 20 mins to make sure all air moves to the front of your paj to get any trapped air out

[gaurav]

Ok guys, here's the latest update.

I got the fully synthetic engine oil, and new Mitsubishi ATF (SPIII) gear oil and also changed the filter and gasket and gear foundation. gear is much smoother and no jerky now.

Good news is the radiator cap inside rubber matting was loose as per other newer cap. So changed and it made a little difference.

But sad part is car still overheating in desert today, but at very slower pace than before and after fully touching the thermo icon top AC cut off and i noticed that no water or coolant overflow neither from radiator nor from spare bottle. As in last incident it all overflowed coz of loose air i guess from rad cap.

Also noticed that AC fan is only running with AC, if car is over heating and i switched off AC to reduce the load but AC fan suppose to work as car is overheating, but no AC fan also went off. Im sure its non genuine.

Third thing that in this model pajero Clutch fan has two speed or only one? As while overheating i noticed that clutch fan was running at regular speed not HI.

Finding: Shall i change AC fan first and test or change both AC and Clutch fan????

[Trojan]

AC fan? Air conditioning fan?

The main fan is variable speed upto and including engine rpm. So, if your running at 4000rpm and the fan is fully engaged, it runs at 4000rpm. They are fairly hard to wreck to be honest with you, but you could replace it for a newer one if you wished. Personally, if I was going to pull the viscous/clutch fan, I'd replace it with an electric unit that will engage on demand and not by rpm/temperature.

40 degrees is a hell of a heat to be contending with and I'd suggest replacing the radiator water with a good quality high temperature/desert coolant as it will transfer heat from the engine more efficiently, even more so than normal coolant from a bottle.

When the truck overheats, do you get a red warning light marked A/C?

[dragon]

could also possibly add a bigger oil cooler but its still very strange as pajeros were designed for such conditions
also im sure they should run only semi synthetic oil but im not realy a specialist with oil types