Mechanics

98 SPORT OVERHEATS ON HIGHW

1998 Mitsubishi Montero

Engine Cooling problem
1998 Mitsubishi Montero 6 cyl Two Wheel Drive Automatic ~150k miles

Hey guys, I've found a million threads about this same problem with all different vehicles, but never found a conclusive answer.


1998 Montero Sport, V6. Not sure of mileage but somewhere in the mid 100's (not sure if its the original engine).

I'll start with the morning. When I crank my car, big plumes of white/grey smoke come out of the exhaust, and the first few times I accelerate through the neighborhood. It also makes a slight gurgling noise coming from the engine bay.

In between work and school (just city driving) and on the main roadway (holding speeds of around 45 constantly) the car works fine. If I get on the Highway/Interstate though, problems arise. Usually when I hit 70 (for about 2 minutes) it begins to overheat. If I drop down in the right lane to about 55 it goes down, and sometimes turning the heater on helps lower it a bit as well. If it continues for too long (5 minutes) then I start to lose antifreeze. And it goes fast.

I've replaced the: radiator, hoses and clamps, and thermostat and gasket. I've also used 3 different kinds of antifreeze. Any more questions about the situation just let me know!

Thanks!
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Jessiah331
October 31, 2009.




Hi Jessiah331,

The grey exhaust smoke is an indication the valve stem seals are worn resulting in engine oil seeping throuth them and getting into the exhaust ports. The oil is not completely burnt thus the grey smoke out of exhaust.

Replacing the seals should solve the problem.

However you have overheating issues and if it is white with coolant losses, there is a possibilioty the head gasket is bad.

Overheating at high speed indicates inefficient cooling and possible causes are : 1. Radiator clogged. Mixing of different brands of coolant can cause the radiator cooling fins to clog.

2. Weak water pump.

3. Improper installation of radiator fan motor, could be turning in opposite direction if wires are reversed.

4. Insufficient coolant in system.

Did problem start occurring before replacement of thermostat and radiator?

You mentioned losing antifreeze, does it happen only when over heating occurs?

KHLow2008
Nov 5, 2009.
I'll try to answer/respond as neat as possible : )
1. I thought the same about the radiator. Replaced all of the hoses, clamps, and radiator itself. No results.

2. New water pump as well.

3. Haven't checked the fan. How's the best way to know? Side by side comparison?

4. When it was loosing the antifreeze: I would check to top it off before I left. When I hit the highway and it was overheating, I'd pull off and look under the hood, and antifreeze was pouring from around the bottom of the engine/radiator. (Not completely sure where, by the time I would get to it, it was almost empty.) If I topped it off and got on smaller roads it would work fine.

When I first got the car I drove it from Georgia to Massachusetts. It ran a little warm, but nothing to be worried about (no loss of antifreeze) It would usually cool off if I turned the heater on.

After sitting for about 2 weeks (waiting on registration) It began overheating on highways. If I pulled off of the highway it would cool off and I could take to back roads.

That was March 09, and I replaced all of the mentioned parts (rad, pump, thermostat, etc) Since March it has ran perfect, on the highway and all. Just recently it began overheating, though not quite as bad as before.

I don't know much about engines, but would the fact that it's colder outside effect anything with the car? It was overheating last winter, stopped in the summer, and now is overheating again. (Or is this just coincidence?)

Thanks!
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Tiny
Jessiah331
Nov 5, 2009.
The fan clutch tends to weaken over time as the fluid inside it dries up and when this happens, the fan is not strong enough to provide the correct amount of air to cool the radiator at high speed.

The check the clutch fan, with engine off, spin the blades to test the resistance. There should be some resistance and not spin too freely. Special sislicone fluids are available for refill but I am not sure if your clutch fan can be disassembled. There are 2 different type, one that is serviceable and another type that is not.

The type that is serviceable would have bolts holding the clutch fan housing, 4 for the fan blade and another 4 for the housing.

KHLow2008
Nov 6, 2009.

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