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Hi, I am having a new problem with my 2001 DHSE - on a run from the country, yesterday, the engine decided to overheat. I had done a run the previous day of around 100 miles with no problems, and yesterday I had been running around a bit, again with no problems.

When I left for the journey home I got about 20 miles into the journey when I suddely noticed that I had no power, and when I looked down I saw the gauge right up in the red, and the red warning lights was on. I pulled in, opened the bonnet and, even though the gauge was right over in the red the fan wasn't running.

The header tank was filled to the correct level, having been checked the day before. So I sat for an hour to let the engine cool somewhat, but it only drove for about another five miles before the gauge, and the red warning light, came back on.

I did notice that, wth the engine off, but the ignition on that I could hear what sounded like the fan running but it wasn't turning, so I presume that this was the viscous fan unit running but not connecting to the actual fan. I wonder whether this makes sense, is it time to fit a new viscous fan unit ?

I checked this morning, with the car having been left overnight, and cold, and when I started the engine the fan was running as normal at start-up. However, when I tried to stop the fan itself I couldn't. When I checked the fan yesterday, when the engine was hot, there was resistance in turning the fan, but not very much as it turned fairly freely. But this morning it is locked in, and it would probably chop my fingers off if I tried to stop it.

It is strange because my engine temperature always sits at the last blue line on the gauge, and usually only went up to the 12 0'clock position in heavy traffic, and I remember, about three months ago, someone on the forum said the viscous fan could be dodgy, because the temperature gauge should always sit at 12 o'clock. My car has always sat just on the last "cold" sector since I got it nearly tree years ago.

Everything is very clean around the radiator and the hoses, to the extent that they look quite new, but the large finned viscous unit looks a fair bit corroded.

Any advice would be appreciated before I start to order replacement parts, I don't want to splash out £500 on an alloy radiator if the problem turns out to be the thermostat.

Pierre3.

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The viscous fan is mechanical and thus driven by the engine - if the engine is running, the big fan mounted to the front of the engine should be spinning. It might be the viscous coupling isnt' locking up, but even then, it should be spinning to some degree. If you say it span freely yesterday when it was hot, then chances are, the coupling has failed. When cold, they are usually stiff, and then free up once the engine is running. But as it gets hot again, they lock up and thus pull more air through the cooling pack.

The electric fans in front of the radiator pack are not for engine cooling - on the V8 at least they can be told to run by the engine ECU when overheating, but I don't know about on the diesel, and either way, they aren't up to much once they've gone through the AC condenser, intercooler and finally the engine radiator anyway.

You may have been hearing the auto box cooler fan tucked down behind the front bumper - late auto diesels had them.

Thing to check in my opinion is that the bottom of the radiator is getting hot - if its stone cold and the fan isn't locking up, then there is no flow through it, so no hot air hitting the viscous coupling. That would most likely be down to thermostat or water pump. If the rad is hot top to bottom, then viscous coupling.

Would be my first thing to look at, anyway :)

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Sloth, thanks for your reply. The suggestion about the gearbox cooler being the noise that I could hear with only the ignotion on could be right. It definitely sounded like a fan running from the front of the engine, and it wouldn't make sense, thinking about it, that it would be part of the viscous fan as the engine wasn't running at the time, and the fan wasn't turning. There was a bit of resistance in turning the fan blades with the ignition on and the engine showing overheat, but not much.

I couldn't freely spin the fan blades but I could turn them without very much resistance. There is more resistance this morning with the engine stone cold - but I can still turn it. I started the engine and tried to sto the fan blades turning by using a big, big, heavy set of gloves [welding gloves] but there was no way that I could slow or stop the rotation of the fan. I really don't think a rolled up newspaper would make any difference, either.

When I turned off the engine again, still cold, I could then turn the fan blades but with resistance.

I am just wondering whether I should just replace the viscous fan with a Rivotec electric fan kit as a first effort.

One thing that I wondered about - when the engine first showed "overheat" on the gauge I waited until the gauge dropped to between the last blue sector line and the 12 o'clock point, and then started driving it again, hoping that the airflow in the evening air [it was quite cold last night where I live] would have been enough to keep the engine cool, but it only did about 5 miles before the gauge was back up at the top of the gauge.

I thought that if the car was moving then there may have been enough airflow going through the radiator to travel a fair distance on a fairly level road, with no trafficand evening cool air. But this didn't happen. With the engine running the gauge started to rise almost immediately.

I am just hoping that there is not another issue such as the thermostat or the water pump. I could see the belts were running well, and, checking the condition of them, they look in good shape.

Finally, one thing that I noticed that you said - I didn't think that the diesel P38 had a fan in front of the radiator, as well as behind it. Am I right ?

Pierre3.

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I'd be looking at the water pump first.
The radiator is quite capable of cooling the engine while moving, even in 30deg c temps.
The water pump has been known to fail with the vanes not turning but outside looking normal, normally the plastic impellor version.

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Tanis, I am thinking along the same lines, I would have thought that the air flow through the radiator should have had some sort of cooling effect, but the temperature wouldn't go down even when I let the car drift down a hill with no throttle and doing maybe 50 mph. The temperature still rose, giving the impression that the coolant isn't moving through either the radiator or the engine block. That, in turn, would certainly seem like a non-working water pump, as you say.

I have just ordered a new pump, and I will fit it anyway, it can't do any harm. I can always fit an electric fan when everything has been put back together.

Pierre3.

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As you have by now surmised, you have no flow through the radiator, so that is either water pump or thermostat. Not sure about the P38 one but modern thermostats tend to fail open rather than closed. As you say, the viscous only really does anything if you are in traffic and there is no airflow through the radiator, moving at 50 mph you hardly need the fan even.

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Hi Richard, now that you mention the thermostat I think that it probably won't be a bad idea to fit a new thermostat along with a water pump.

Thinking about why the overheating happened, and what happened afterwards really does suggest that there is no movement of coolant through the engine and radiator. And the fact that the temperature rose so quickly after parking up for nearly an hour would suggest that the coolant wasn't circulating, and there are kind of three main culprits stopping circulation, I guess - the water pump, the thermostat or the radiator. I know that I am leaving out the heaters but I am looking at the situation in a logical manner - what was it doing before; how did it happen at the time; and what happened after.

The temperature gauge had shown rather odd readings in the past, but I did think that this was fairly normal, as I have seen similar readings on other work vans and 4x4's, especially when loaded down with tools and gear. So I didn't really think a lot about it, as the engine never got especially hot.

Anyway, I think that having put it down here it sort of makes it easier to consider the problem, and the solution, rather than constantly just thinking about it, in one's mind. Well, in my mind anyway, as all there is in there seems to be a chicken sandwich and a copy of "Parade" magazine !!

Apart from Rimmer Bros's genuine LR water pumps, at around £270 what other water pumps can be recommended ? Just reading through loads of posts water pumps from the main online sellers don't seem to get great reviews - Meyle, or Hepu, or KS.

Pierre3.

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going by the time that it boiled i would start with the thermostat first as this is the most likely thing followed up with the pump .
also just as a note, i think i read that diesel radiators have a baffle in the top of the radiator and it can fail and the coolant doesn't circulate in the radiator , it;s simply in one end and out the other , just an FYI.

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I recommend a new O-ring for the rigid heater pipe that goes into the block just by the water pump while you have all that stripped out it is part no. PES100150L.
I can tell you that cooling on a P38 diesel can be a struggle, in the last 3 years I have renewed everything, W/pump, fan, ally rad etc. and yet towing (admittedly a probably overweight) trailer back up from the south of France I still had to slow right down on the hills, I could keep the speed up but revving over about 3500 for prolonged periods was guaranteed to see the needle creep into the red.
Also note that a hot M51 uses quite a bit of oil which is essential to good cooling, recommend you check the level there after your troubles.

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I think this is the one I used. Metal impellor on it.
https://www.eurocarparts.com/p/circoli-water-pump-201110161

May as well do thermostat at same time.
The time taken to strip down will pay for itself.

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Hi guys, thanks for all the information.

Blanco - I have ordered the heater pipe o-ring, as suggested. Good advice to do it at the same time.

Tanis - I have ordered a water pump by Dolz, supplied by Micksgarage. I was torn between ordering from Rimmer and getting an exchange pump, but the cost of a pump and a LR thermostat would be €220, plus delivery €40, plus VAT, courier admin charge, and duty when it arrives in Dublin. I would image that I would be looking at around €400 just to get the items here. Then my time fitting them.

I looked carefully at the workshop instructions and I am going to risk not using an LR water pump, and hope that it works OK. The thermostat is made by Gates, who do seem to have a good reputation.

What I would like to get some advice on, is the thermostat - the workshop manual says to replace a small o-ring which [I think] is connected to the turbo or air inlet tubes, but it doesn't give a part number.

I wonder whether anyone might have this part number, or part description ?

Also, are there any seals or gaskets required for the thermostat housing ? Again, if possible, the part numbers would be much appreciated.

Pierre3.

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@Pierre3 I believe the hose for the thermostat don't have any gaskets or O rings the pipes are just straight connectors

STC2194 is the thermostat housing to head of ring
https://www.lrdirect.com/stc2194-o-ring-thermostat-new-rr-2-5dt

hope this helps

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Iirc both of mine came with o-rings

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Hi guys, thanks for the help.

I think that I may have identified the possible problem which caused the over heating:
enter image description here

enter image description here

I have a real feeling that these two parts shouldn't look like this ! I have considered getting my special rubber glue out, to fix everything but I suspect that that solution may not actually work.

Now I have had to sell one of my children to buy a new water pump. Oh well, that will be less on food !

Pierre3.

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At least you have a definite problem there, so you know your looking in the right place now.

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Couple of years ago I LPG converted a(nother) Volvo T5. After giving it a good booting during LPG calibration it started over heating, problem soon getting worse so that it started overheating at idle and finally during just slow cruising (so very soon it had no cooling at all and would overheat under any conditions). I diagnosed a failed waterpump but because I was so busy with LPG conversions I farmed the water pump replacement out to a local mechanic / garage. He found that the impellor had broken up similarly to your impellor.

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I was fairly pleased to actually see this, because, as you rightly say, I have a definite reason for the engine overheating. At least I don't have to go changing all the other bits like the viscous fan and the radiator. I will fit a new thermostat though.

On this issue - is there any reason not to use 100% orange OAT coolant, and not have to water it down ? I just happen to read other posts, elsewhere, saying that owners have used a 50/50 coolant water mix, but my experience has always been to use 100% coolant. There was orange coolant in the system when I drained it yesterday.

Pierre3

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I would think water is the better actual coolant, other stuff is there more to protect against corrosion and as anti-freeze.

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Depends what you buy, some will be marked as Coolant, and is already 50/50 water, others, usually only slightly more expensive, will be marked as Concentrate which you add your own water to. You just need to read the label carefully to see what you are getting.

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I think he means can he put 100% concentrate in (no water)..?