Non merc. Temp sender question?

[brucemillar]

Folks.

I have an aftermarket coolant temperature gauge and sender fitted in my 3.5 V6 Pajero. The sender is fitted into an adapter placed in the radiator top hose.

Now here is my question. The gauge shows that the coolant temp varies between 88 > 95 c. Uphill or traffic 95. Free running 88>92c.

This seems high to me?

However. I have fitted a new 82c Stat. Flushed the entire system. Checked the heaters run hot & cold etc. All seems ok. I also fitted a new rad cap.

The factory fitted gauge reads fine. The sender for that is mounted on top of the V/engine.

So. Am I worrying about nothing? Is this an expected temp?

There are no indications of anything amiss. Indeed, were it not for the gauge I would be blissfully happy.

FYI. I have tried another gauge and sender and re-wired them both. Both give identical readings.

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[hotrodder]

Sounds ideal to me. Ancient stuff aside most engines are designed to run similar coolant temps as it improves efficiency etc. Many (most?) modern cars have a temp gauge that doesn't tell you the temp (just hot or cold) if they have one at all

Adding glycols to water raises the boiling point slightly as well as lowering the freezing point. Automotive antifreezes also contain corrosion inhibitors for the obvious reasons
Glycols aren't as good as water with regards to heat capacity and thermal conductivity which is why a 50% coolant mix is about the 'strongest' recommended*. This boils at ~ 107°C at standard atmospheric pressure. Raise the pressure and the boiling point rises further... with a 12psi cap a 50% solution boils at ~ 126°C, at 15psig ~ 129°C and at 20psig boiling point is ~135°C
Have a fan or two kick in to increase airflow across the rad when coolant temps reach/exceed 100 - 110ish °C and the engine is kept within a fairly narrow temperature band provided everything is working properly and the rad is a suitable size etc

* unless you're a snake oil salesman and invent all sorts of BS to sell neat glycols at insane prices as a 'cure all' waterless coolant

 

[brucemillar]

Hotrodder

What a great reply thank you. What now worries me (I am like an old woman now) is that others are reporting their Pajero's (same engine) peak at 88 > 91.

Had I never asked I would never had got the answers and may never have worried.

Apparently Mistubishi deliberately restricted the factory fitted gauge so that it only rises above half when the temp reaches 120c . This was done to stop people panicking. Problem is that at 120c you may well have cooked the head. So the Pajero owner's recommend fitting an aftermarket gauge and sender to the top hose. I am not convinced that the top hose is the best location as it will always read hot?

I am also about to test my rad with an infra red thermometer to see if I have any cold spots. There is zero room to get my fat hands down there to check.

 

[grober]

When temperature varies with load/ road speed it can mean your radiator cooling is marginal. This can be inherent in the design or may mean part choking of some of the coolant tubes. This can occur if the radiator is allowed to gradually dry out say if its taken off the car for an extended period of time. Can be reversed by a power backflush together with strong internal cleaners but if that corrosion sludge has had the chance to consolidate into a solid internal coating/plug can be difficult to shift in modern radiators with narrow coolant tubes.

 

[toolman1954]

Hi,
with all that has gone on before with your Pajero, I would think you are getting a trifle paranoid about anything else that might go wrong with it. Rebuilt engines need a few miles to bed in, but if anything was wrong, it would have manifested itself by now. I am sure Simon would not have given it back to you if he was not 100% happy with it.
You have really answered your own questions when you say that the top hose is not the ideal place for a temperature gauge sender, it is not, but it is as best as can be for a rough guide. As you are quoting exact temperatures I presume that the gauge is marked out in degrees, how many modern day cars have exact degrees on them? Temperature variations between similar cars with the same engine can vary with type / make of radiator and the efficiency of the radiator to cool down the coolant. A few degrees either way in the great scheme of things is not going to make any difference. Perhaps your Pajero is running exactly right and the others are running too cool perhaps their gauges are calibrated differently? does it matter, no of course not.
What does matter is that you have your Pajero back and it is running again so that you and the dogs can get out and enjoy it.
Perhaps now you know it is running right, and Hotrodder seems to agree, then just put a wee hood over the temperature gauge and do not keep your eye on it. Sometimes too much information can just make you worry about things that are just not going to happen.
Regards Steve.

 

[hotrodder]

Coolant temp as it's leaving the engine is more useful than a temp measurement from somewhere cooler. Thermostat housing, by the water outlet in the cylinder head/inlet manifold/valley of V engines or top hose are all good spots imo. Less useful than the actual cylinder head temp in some respects but obviously related

As said differences of a few degrees could just be tolerances/calibration of senders and gauges or a rad that's seen better days. Personally i wouldn't worry about it until the weather starts warming up in 6 months or so and then only if it struggles to maintain the current running temps/gets hot in traffic
What sort of rad design is it; vertical flow, single pass horizontal (inlet and outlet diagonally opposite corners) or horizontal flow double pass (inlet and outlet on the same side)? With either of the first two i'd expect slightly more of a temp variation across the core as they're less efficient

Should've mentioned last time that the main job for the rad cap is to prevent coolant from being puked and/or boiling after switching off a hot engine. And to help when idling in traffic. At higher rpm the pressure in the block and head is raised by the thermostat restricting flow out of the engine even when it's fully open*. This is what prevents steam pockets from forming around the combustion chambers where temps are a chunk higher

Overkill for watercooled road cars as they tend to suffer more in heavy traffic if the cooling system is neglected but as an aside with piston engined aircraft and/or aircooled engines it's relatively common to monitor cyl/head temps with a thermocouple at the base of one or more spark plugs. Off the top of my head temps are typically gonna be in the ballpark of 180 - 220ish °C continuous (under load) and an absolute (short term) max of 250ish? Unlike road cars aircraft and aircooled engines are more prone to overheating under full load
Obviously F1 is in a different league with regards to attention to detail etc but Inside an F1 Engine - Racecar Engineering might put you at ease with regards to coolant temps. Higher pressures (rules allow upto 3.75bar / 54psi for a boiling point of ~141°C), no glycols and they want the coolant temp around 125°C

* Rated thermostat temp is when it starts to open, typically takes another 15 - 20° to fully open

 

[brucemillar]

Hotrodder, Steve, All

Your replies are brilliant and educational as well as comforting. I am by nature paranoid. Steve your on the money. My recent experience with this truck has made my hyper-sensitive. Simon was not concerned and indeed was sure (as am I) that this is not a big issue like a head.

However. We never really found out why the head went in the first instance. These trucks biggest failing is head gaskets. Partly due to running twin heater matrix (front & rear) sludging is common.

My new (well I just had to) infrared thermometer shows cold spots on the rad. So I may go for a pressure flush. New rads seem hard to find. The Blueprint ones do not fit. A new one from Mitsi £730. Ouch.

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[hotrodder]

What about Nissens? £120 - £130ish by the looks of things and while i dunno about Pajeros the one i fitted to my s124 a couple of years ago fitted perfectly. Quality wise it wasn't (cosmetically) as nicely finished as the origional Behr (500ish from MB IIRC) but instead of copper reinforcements bonded into the inlets/outlets it had thicker wall plastic instead which is better IMO

Probably not gonna help any paranoia but i'm not impressed with the design/layout of the rad... vertical flow effectively wastes a chunk of the available core and the top tank is tiny which wouldn't be an issue if it a had a proper header tank but it looks like the cap is in the rad i.e. slight loss of coolant or if the expansion tank doesn't draw coolant back in as it cools down and more of the core is wasted as soon as the coolant level drops a little

 

[brucemillar]

Do you have a link for Nissens?

Ignore this. Just found it. Poxy spell check.


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[brucemillar]

Okay, an update:

I spoke to Simon last night and agreed that I would swap the factory and aftermarket temp senders to see if we could change the gauge readings and rule out a gauge fault.

Did that today. So now the aftermarket gauge is reading from the top of the block. The factory gauge is reading from the top hose.

Both gauges still read the exact same. SO this would rule out a sender or gauge placement issue.

Next I ran the car up to full temp (now showing as a steady 95c)

I used an infrared thermometer to check the radiator temp side to side (left to right)

The left side is showing 58c the right side 98c. Checking the temp at the sender shows 93c at the sender.

So my rad is blocked. I am now phoning around trying to find somebody who can either repair or replace my rad as I cannot afford £750 to Mitsi for a new one.

 

[grober]

I would recommend BEHR /HELLA as a good aftermarket supplier.
Unfortunately HELLA SERVICE UK don't seem to cover BEHR radiator products.
I dare say you could order from abroad/ Germany ???
I think they do a suitable replacement for manual gearbox Pajeros ???
but check the catalogue for details - size? 8MK 376 -770-391
Online Catalogue | Behr Hella Service GmbH

 

[grober]

dup

 

[brucemillar]

Size is: 500 deep x 600 wide.

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[KennyN]

What about this place - High Performance Cooling by Serck Motorsport - they may do a universal rad that can be adapted to your vehicle.

Kenny

 

[grober]

Size is: 500 deep x 600 wide.

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catalogue dimensions for 8MK 376 770 391 for 6g72 engine

 

[Bellow]

I used an infrared thermometer to check the radiator temp side to side (left to right)

Is the top to bottom temp gradient not the the relevant parameter here?

I'm with HR re temps. ie they are about right given the propensity for highish coolant temps to minimise heat loss from combustion and thus improve efficiency. (Vauxhall IIRC were running temps of 100C.) Winter is hardly going to tax the cooling system (but the salt will attack a new rad) so why not wait until next year when the ambient temp rises and see where it's at?

 

[brucemillar]

catalogue dimensions for 8MK 376 770 391 for 6g72 engine

Graeme

Nope that will not fit. I just went and did a proper measure up. Mine is bang on 620 across x 500 deep. It fits into some heavy duty mounting plates that are bolted either side and not top and bottom.

FYI: Nissens do not do one.

 

[brucemillar]

Is the top to bottom temp gradient not the the relevant parameter here?

I'm with HR re temps. ie they are about right given the propensity for highish coolant temps to minimise heat loss from combustion and thus improve efficiency. (Vauxhall IIRC were running temps of 100C.) Winter is hardly going to tax the cooling system (but the salt will attack a new rad) so why not wait until next year when the ambient temp rises and see where it's at?

I hear you here and were it not for the appalling record of these engines blowing heads I would happily wait/chance it. This all started with a blown head gasket. 6 months later I am still picking up the pieces, Were I to blow it again for a radiator I would have to shoot myself.

 

[grober]

Well your only option would appear to be see if someone like Serck can recore it for you? Certainly worth paying your local Serck Services depot a visit?

 

[Bellow]

Didn't CM get his W114 rad re-cored recently? And a good job done on it too?