Diesel engine cooling & thermostats

[man of kent]

There is a massive 100+page discussion on the BMW cooling and thermostats eslewhere. I'm starting something new as I think we may be barking up the wrong tree! Big talk, so think about this (designed some of my own cooling systems).

Firstly, nothing to say about THE thermostat and which type. Lets discuss the cooling of the BMW diesel. From numerous comments in the BIG discussion:-

Known facts:-
a)All engines develop heat including diesels and the BMW diesel
b)The radiator is the same on the diesel and petrol engines (checked the Rimmer part no P00000960 which is common)
c)The engine does heat up - eventually
d)The fuel consumption deteriorates in the winter - numerous comments
e).....so the radiator does cool the coolant in the winter, so heat is produced unlike what BMW say.

Non fact or not proven:-
a)BMW say that their engine is so efficient it does not produce enough heat. Why only their engine and not other diesels?. Vorsprung technik boasting? Probably.
b)can the BMW diesel take high temperature running so runs cool deliberately? Some engines are known to blow gaskets at high running temperatures. You cannot assume the BMW will unless proven to be OK at the more normal 100+ degrees C.

My personal view is that there are some design errors which are misinterpreted as a non heat generation/thermostat problem. What I find of interest as a designer is that the radiator is common on the petrol and diesel and yet the heat generated is different. Almost certainly the reason for that is cost saving. Why pay extra to have a smaller radiator on the diesel with expensive body changes when running cool does not damage the engine.

So they built petrol and diesel prototypes with the same engine and found the diesel runs too cool and they want to start production without too many changes to the body assembly asap. (Late body changes are a no, no due to long lead tooling time). So, did they modify the electronics to get the instrument panel temp gauge to show normal when it isn't on the diesel?. Very strange. Was the quickest & cheapest, taking into account production issues, solution to add components such as the FBH which would mean no body changes?. Dont forget that Rover had no previous test results on a transverse fitted BMW diesel and probably nothing from BMW other than "you will use our diesel". You cannot assume that somebody did the heat calculations as when I worked at IBC and they tried on some prototypes the VM motori diesel in the Vauxhall 4x4, they used the same radiator as the Isuzu and the VM motori engines blew up! Just because it was the wrong radiator! Rover cooling system designers probably had their hands tied behind their backs by BMW.

Now, not having access to the facts from BMW/Rover, this is my opinion and could very well be wrong, but some of the issues above are a bit 'strange'.

So what am I saying? I think its a basic problem of the radiator being too big/efficient on the diesel. Its difficult to prove this because the IP temp gauge does not read accurately for an unknown or proven reason. I'm unable to do anything in the garage at the moment due to a mjor op, but I am going to start blanking off some of the radiator when i can and look at the temp from the instrument panel diagnostics. If the temp does not go up when blanked off, then the BMW engineers are correct and the BMW is super efficient and they are brilliant and have found a non friction engine!. If the temp does progressively go up the radiator is just too big.

Now even more of interest and worthy of comment. Maybe there is nothing much wrong with most of the thermostats that have been changed in the past. Perhaps its just a case of the engine running too cool because of over cooling? Thermostats are normally very reliable and I dont hear of BMW owners having to change thermostats.

This is just an opinion for thought and we will probably never know unless proper tests are carried out. No doubt this will grow into 100+ pages ??

I'm now waiting for the explosion of comment..............with anticipation.

[man of kent]

Small slip..........built the petrol and diesel protoypes with the same RADIATOR, not engine.

[wuzerk]

I have just proved conclusively that the Diesel is quite capable of running at
95-99C in normal running conditions by experimenting with a 205F (96.1C)
STANT thermostat. My engine would easily run at around 93C rising rapidly to 97C when under load when the 'stat would open. I do not see what the size of the radiator has to do with the attainment of a decent running temperature since it is not in play until the thermostat opens,unless the fact that the engine is mounted sideways instead of fore to aft as designed means that more incoming cold air hits the side profile of the engine? The answer to that question would be to hear if the same engine mounted fore to aft actually runs hotter.

[BarryH]

Originally Posted by wuzerk

I have just proved conclusively that the Diesel is quite capable of running at
95-99C in normal running conditions by experimenting with a 205F (96.1C)
STANT thermostat. My engine would easily run at around 93C rising rapidly to 97C when under load when the 'stat would open. I do not see what the size of the radiator has to do with the attainment of a decent running temperature since it is not in play until the thermostat opens,unless the fact that the engine is mounted sideways instead of fore to aft as designed means that more incoming cold air hits the side profile of the engine? The answer to that question would be to hear if the same engine mounted fore to aft actually runs hotter.

I agree completely. I have thought for many years that a transverse mounted engine takes longer to reach running temperature than a comparable in line one.

[sikelsh]

I have had mine up to 114 degrees while sat in static traffic after towing the caravan back in the Easter/May Day holiday, I have no working cooling fan, my bottom twitched a little but she kept moving, and thankfully the traffic cleared so I could get some airflow in, 20,000+ miles no sign of an issue.

Since worked out that If I put the heater on full in Econ, this now expels the heat, but thats not related to this thread.

Simon

[Singvogel]

As a retired university lecturer on air-conditioning installations, I am finding
this discussion on stats & temps amazing - the other thread has reached 116 pages and 68,900 + views.

I imagine this one will be a 'long distance runner' too.

Have we looked at the other vehicles using this M47-320D engine? Do their owners have any issues temperature-wise?

I'm talking chiefly about the extremely popular BMW 320D and 520D, plus of course the Freelander TD4 which is also a transverse fit.

I have extensive personal experience of the TD4 in extreme temperatures both high and low. On several examples I may add.

Amazingly there are no situations where the running temperature was ever a cause for concern. The heater is adequate in my opinion.

Exactly the same engine code name M47R 1951cc with no technical updates.

An oversize radiator, an fbh, and a 82C stat - so 5 hours Zagreb to Belgrade in Summer with an outside temp of 38c at cruise speed of 85-90 mph with AC at full blast is no problem at all. The electric cooling fans don't even keep running when you stop at a services!!

Likewise in Winter in Kosovo at -28C the beast fires up immediately, the fbh does its stuff, and within 3-4 miles is throwing out heat to the extent that the max temp and max heater blower-fan setting can be reduced.

I have a Scangauge 2 fitted so have a constant digital temp readout via the OBD - it never moves much from 82C and it doesn't seem to matter whether it UK or some more extreme place. I also monitor the temp of the air coming through the fascia vents with a dial display air-conditioning thermometer probe permanently installed in the centre outlet.

I am at a loss as to why things are apparently so different with the 75 and the ZT.

What on earth else is there sufficiently different about the spec to give such a problem to so many owners?

Anyone with any BMW 320D experiences?

[James.uk]

The rad on my diesel ZX is bigger than the 75 rad, and has a HUGE cooling fan, but it produces much more heat from the heater...

AFAIK, the thermo is original in my car (75) and works just fine at 160K. miles..
...

[scouseeric]

Originally Posted by James.uk

The rad on my diesel ZX is bigger than the 75 rad, and has a HUGE cooling fan, but it produces much more heat from the heater...

AFAIK, the thermo is original in my car (75) and works just fine at 160K. miles..
...

As does the bro in laws 170k r75. I think its the luck of the draw with the oem 'stats James.

Eric

[man of kent]

Originally Posted by wuzerk

I have just proved conclusively that the Diesel is quite capable of running at
95-99C in normal running conditions by experimenting with a 205F (96.1C)
STANT thermostat. My engine would easily run at around 93C rising rapidly to 97C when under load when the 'stat would open. I do not see what the size of the radiator has to do with the attainment of a decent running temperature since it is not in play until the thermostat opens,unless the fact that the engine is mounted sideways instead of fore to aft as designed means that more incoming cold air hits the side profile of the engine? The answer to that question would be to hear if the same engine mounted fore to aft actually runs hotter.

Makes sense what you say, but if people have had stats stuck open and the engine never gets above 50 degrees C, doesn't this say the rad is oversize on the diesel? Even though in theory the stat stays shut until it reaches the stat temp, there is always a heat transfer to the cooler parts of the engine including the rad with the stat closed and thus the heat up will be slower. You dont get one half the engine at stat temperature and the other half stuck on ambient. If you did there would be all sorts of component stress cracking problems. You cannot always detect this from touching various components as the outer skin can be cold and the inner warming up dependent upon the material thickness. Maybe the transverse mounted engine does get more cooling as you say in which case the rad is oversize! The problem with this argument is that the engine packaging and body designs are so different you dont know how the systems will work until you try them which is why you have prototypes to test.

I still come back to all rads on the 75 being the same with petrol engines developing more heat. Additionally as mentioned above, the other vehicles with the engine do not suffer this problem so its unique to the 75 and MG ZT. The difference, the cooling system. If the stats are the same that leaves the hoses and rad or the posioning or shielding of them. The 75 might have a direct air flow whereas other vehicles might have various obstructions to the air flow. I'm sure its the rad or the packaging around it thats different.

Although some people might find this boring, there are many 75 owners out there with poor heater operation and all we are trying to do is find out why. 100+ pages does say there is a problem and my theory is just another...........different one.

[wuzerk]

Although some people might find this boring, there are many 75 owners out there with poor heater operation and all we are trying to do is find out why. 100+ pages does say there is a problem and my theory is just another...........different one.

I think that we know why, it is usually because the original thermostats start to open permaturely. The cure, to get the running temperatures back to around 88C is to change the thermostat(awkward) or fit the additional 'stat in the top hose. This is easy to do and also easy to restore to original if needed so I,
for one do not consider it a serious problem any longer. Cool running is a common problem with our 75 diesels but it may apply to certain batches of
thermostats for all I know since some owners have never had problems over huge mileages which perhaps suggests that the earliest models had better 'stats? I don't know. I do know exactly when my original 'stat failed which was when I blasted up a long hill at very high speed when the engine reached the highest temperature i had every achieved. Going back down that hill the temperature gauge failed to ever reach the 'normal' position again. I think because the return spring lost some of its strength.