Slow Warm Up

[Jim Hannah]

Hi,

I've just changed my water pump and flushed my radiator. All went well, but I am not convinced that there is not some kind of airlock in the system somewhere. It's an NS 3.2 did. I have good heat from the heater system, so there is obviously no airlock in the heater matrix, but the car now takes a long time to reach normal operating temperature, around double the previous distance, and there seem to be a lot of creaking cracking noises from around the exhaust turbo area. Concerned by this, I partially drained the system and replaced the thermostat with a genuine mitsubishi one, then carefully refilled again, but there is no difference. I think the temperature guage needle now sits about the thickness of the needle lower than it used to, just below the halfway mark. And it takes about ten kilometres to get there from cold.

The top radiator hose gets hot normally, too hot to hold for long, but the bottom one I can keep my hand on indefinitely...even when the engine's been running for a while.

Is there something I'm missing...perhaps a bleed screw high up somewhere? TThis all follows on from my inlet manifold clean, but I can'te imagine any connection with that? Any thoughts appreciated.

Jim

[nj swb]

What did you use to refill the radiator?

Different coolants have different "thermal capacity", meaning any given volume of coolant will hold a different amount of heat at any given temperature.

So what?

Under any given set of conditions the engine produces a certain amount of heat, most of which is dissipated via the radiator. Pure water will hold more heat than ethylene glycol (for example) at the same temperature - or will hold the same heat at a lower temperature. So if your new coolant mix has a greater heat capacity than your old mix then it can dissipate the same amount of heat without reaching the same temperature - and can dissipate more heat at a lower temperature.

[Jim Hannah]

I hear what you are saying; I'm using the green mix, the correct stuff as far as I'm aware, and certainly since the mix had been topped up a few times over recent years, it will be a stronger mix now than the stuff I dumped, but I would expect only a few degrees difference. the thermostat is a 76.5 deg one, precisely the same as the original.

I'm most concerned about the creaking and clanking (expanding and contracting metal somewhere). The vehicle has always done that, as most do when cooling down, but I'm getting these sounds while the engine is running now. Is the turbo water cooled? how can I be sure there's no air lock somewhere up high in the engine or the cooling system in general?

[aussieintas]

Jim

Turbo is oil cooled not water cooled.

One way to check there isn't an airlock is have the car pointing up a slope, or use ramps or jack up front. When engine cold open and leave off radiator cap and start engine. Leave running until it gets hot. That should allow any bubbles present to tarvel through the system and escape at the now highest point being the open cap.it will take a good 20 minutes or so for Pajero to get hot enough.

[erad]

It is winter you know - even in Queensland. I have a NW diesel, and where I live, at this time of the year, it can take up to 20 km before the temperature gauge reaches normal position. I was recently in Sydney and was amazed at the relatively short time and distance that it took to get to temperature.

[Jim Hannah]

Thanks guys. After I allowed the car to cool down this time, I noticed that it had drawn in about another 250ml or so from the expansion tank, which I subsequently topped up. I'll try letting it warm up with the front end up the ramps tomorrow, and see if I can encourage any more air out, just in case.

As a matter of interest, I also have a 2.5 Triton, which reaches normal operating temperature in about half the time, another part of the reason I was a bit concerned.


Jim

[Jim Hannah]

It is winter you know - even in Queensland. I have a NW diesel, and where I live, at this time of the year, it can take up to 20 km before the temperature gauge reaches normal position. I was recently in Sydney and was amazed at the relatively short time and distance that it took to get to temperature.

Well, I hear what you're saying, of course. Our mornings are currently about 15 deg or so here in Central Queensland. I'd expect a car to take a bit longer to reach operating temperature in Syney, with the morning temperatures being about five degrees less?

[aussieintas]

Down here in Tas my NS takes around 15 to 20kms to full temp. Each car is d iufferent so dont judge it to the Triton bud.

[erad]

Further to different cars, my wife's Outlander (2L petrol) is pumping out warm air within 2 km of driving. My Pajero requires at least 5, probably more like 8 km before I can notice any real warm air coming into the car. Mind you, the Outie doesn't have a temperature gauge so I have no idea as to when it actually does hit proper operating temperature.

[spot01]

When you say "green mix" do you mean genuine MMAL green or some other brand of green? Is the water pump genuine? What else did you change, eg, I assume hoses, belts, etc? New belts stretch quickly & need checking.

Unsure if its possible in the Paj, but years ago someone I knew put the thermostat in wrong way around in a Datsun, which then didn't work properly.

Thermostats are a horrible mechanical thing, prone to altering or playing up when they get old, as they operate in an extreme environment. Sometimes their operating characteristics change over time, eg, slower to open, sticking closed or part open, etc. Do you still have the old thermostat? If so, suspend the old & non genuine thermostats (which isn't in the car at present) in a pot of water & bring to the boil. You should be able to see them opening as the water reaches the specified opening temperature. This will help you determine if there is any difference between old & new. If the same, then the issue is elsewhere.

10kms to warm up in a mild climate is about what I would expect based on the 5 NT, NW & NX I have had. Note the gauge isn't really showing the proper linear temperature readings - they are set to distort the readings. All my cars sit just below half to right on half - they varied a bit from car to car. The thermostat might have changed spec slightly as time went on - MMAL are constantly making slight adjustments to all sorts of things over time due to in field experience and issues that come up. I've noticed various subtle differences over my 5 cars, even though they are all basically the same vehicle.

[Jim Hannah]

Actually, I've had another thought...does anyone know exactly how the fan works? It's a viscous coupling type. I've suddenly realised that it may be functioning at full speed all of the time, thus slowing down the warm up time.

[aussieintas]

Here's something I found on the internet that explains it simply.

"The thermal or viscous fan clutch operates in response to underhood temperatures. As hot air blows across the radiator, it heats a thermal spring@*$#mounted at the front of the clutch. As the spring is heated, it turns and allows valve ports to open within the clutch. Silicone fluid stored inside a reservoir is allowed to pass through these open ports and enter the working area of the clutch. This engages the clutch and drives the fan. Once the engine is cooled down, the thermal spring rotates back and closes the valve ports, disengaging the fan".

But don't be fooled as the fan spins all the time with the engine running. Very hard to tell the difference visually between freewheel and engaged when spinning. Below is screenshot from the manual.

[4ePikanini]

Petrol engine warm up a lot quicker than diesels

Diesels at low load generate very little heat to the cooling system

Modern egr systems utilise the egr cooler to heat the coolant quicker on warmup

A blanked egr will delay engine warmup

A low load efficient diesel will take ages to warm up.

If the A/c is off and the heater on, and you just let it idle, a pajero will never reach operating temp at below 25 ambient.

The pajero has a huge cooling system to cool atf and engine when towing mac capacity. It takes a lot of heat to get the small circuit up to temp. Especially when the heater is on as its dumping heat via the heater matrix.

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