XSeries-forum

I have checked and double checked your coolant system on my parts catalogue and there is no reference to that part. As for snrbrtsn post on transmission oil cooler, I have googled that and can only find a thermostat for gearbox oil cooler for the V8 engines.

The transmission oil cooler is there according to Realoem however as far as I am aware it is just a cooler and has no stat in it.  It is very small, a few inches, and makes no material difference to the overall water temp.  It certainly won’t hold the temperature that far off that expected from the engine stat.  There is a similar rad at the rear of the oil filter assembly.

If someone would like to comment on item 4
Not seen anything like this before and what roll does it play. It's listed as a thermostat.

http://www.pelicanparts.com/techarticle ... lacing.htm

I’m not going suggest this is most definitely the cause if you’ve replaced the main thermostat to no gain,
I’ll onpass knowledge from my E60 day’s, where the Egr thermostat would become a service item and the main stat required changing annually just to maintain temps, the dpf was sensitive to engine temps for the regens, ( I appreciate the E53 doesn’t have a Dpf)
Many attempts were made at increasing the engine warm times including the installation of A N other inline thermostat which worked in part though did mask the as yet undiagnosed and underlying issue, until one day “a member” had the incline to delve deep and tackle the transmission cooler thermostat, many laughed many sniggered though all were in disarray at the improved temperature reading and warm up times, as such many followed and sales of said items went through the roof, whilst at the same time frequency of change to the EGR stats  deminished, with a fairy tale ending all enjoyed quicker warm times, steady and maintained temps circa 85-90 degrees under varying loads  :xmaswink:

Trying to read across lots of parts diagrams, I think the engine cooling is only connected to the two hoses on the rad (top right, middle left side) with water flowing across rather than vertically as used to be done.  The output and return from the engine cooling water pump to the rad and back to a connection part way back on the right side of the head under the inlet manifold.

Part 4 could be this odd stat for the transmission radiator/cooler, but I cannot see what it directly connects to.  It doesn’t appear to be in the main coolant loop.  It’s used on a number of cars (E46 and E83) and could connect into the expansion tank.  All the group references are for the expansion tank - hence my assumption.  What it is for I am not sure of.

Another option for item 4 is to do with vehicles with Aux Heating - all diesel E53s have the Webasto unit - as that might connect into it.  That loop also feeds the internal heater matrix for the cabin.  So is that loop stuck open?  It doesn’t seem to have a loop thermostat but it does have two motorised valves and an extra pump.  Would that be enough to keep the whole system cold?

What happens if you turn the car heating off?  In the good old days you could keep an overheating car cooler for a while by turning the heating (and cabin fan) to max as it provided another radiator.  OK you needed to open the window so you didn’t cook, but you might see where I’m going with this.

It doesn’t explain the stuck stats though  ???

[quote="henrym3"]
If someone would like to comment on item 4
Not seen anything like this before and what roll does it play. It's listed as a thermostat.
[/quote]
Type the part number into google, that may help

appreciate all the effort that is going in to resolve this, folks. Im open to all ideas, albeit that Im doubtful that an oil cooler would hold the temp down that much, and even if it did, then surely my main stat would stay closed to compensate?

Anyway, an update from my end. I decided to retest the two stats I have off the car before I return them to the garage as they need then to get a refund from their parts supplier. I had previously stated that both were in different positions - this is partly due to the fact that I think both are knackered and partly due to the fact that they are slightly different so the bit that extends in/out sits in a slightly different starting/finishing position. Anyway Stat number 1 appears to do nothing - even when the temp gets up at over 100c it doesn't move. I then immediately ran it under cold water but no reaction
Stat number 2 appeared to open at around 96c and then reacted immediately and closed when run under cold tap. however it did this twice (as I wanted to see repeatability/reliability), and it gave up the ghost and doesn't work at all now.

So, Im thinking that, if for no other reason to rule things in/out, that I go and order a Behr/Mahle thermostat and bench test it first to see that it opens/closes repeatedly at the required temp, before fitting it to the car. if I know it is working before I fit it then, in theory at least, I don't need to revise that and can rule it out, whilst I search for other solutions

Smee

I think you should be reasonable confident that a good thermostat will sort the problem. Although when testing I don’t think you should shock the new one with cold water, just let it cool down and check it closes


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[quote="henrym3"]
I think you should be reasonable confident that a good thermostat will sort the problem. Although when testing I don’t think you should shock the new one with cold water, just let it cool down and check it closes


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[/quote]
+1

[quote="X5Sport"]
Trying to read across lots of parts diagrams, I think the engine cooling is only connected to the two hoses on the rad (top right, middle left side) with water flowing across rather than vertically as used to be done.  The output and return from the engine cooling water pump to the rad and back to a connection part way back on the right side of the head under the inlet manifold.

Part 4 could be this odd stat for the transmission radiator/cooler, but I cannot see what it directly connects to.  It doesn’t appear to be in the main coolant loop.  It’s used on a number of cars (E46 and E83) and could connect into the expansion tank.  All the group references are for the expansion tank - hence my assumption.  What it is for I am not sure of.

Another option for item 4 is to do with vehicles with Aux Heating - all diesel E53s have the Webasto unit - as that might connect into it.  That loop also feeds the internal heater matrix for the cabin.  So is that loop stuck open?  It doesn’t seem to have a loop thermostat but it does have two motorised valves and an extra pump.  Would that be enough to keep the whole system cold?

What happens if you turn the car heating off?  In the good old days you could keep an overheating car cooler for a while by turning the heating (and cabin fan) to max as it provided another radiator.  OK you needed to open the window so you didn’t cook, but you might see where I’m going with this.

It doesn’t explain the stuck stats though  ???
[/quote]

Ok, so here is some new news on this. Taking Richard's point, I switched the car heating off and the engine is now running a good 5 or 6 c hotter, albeit not hot enough. Where I previously had 68 or 69c Im now seeing 74 or 75c.

So what does this actually tell us ..... (if anything)?

Don't see that it tells you anything other than you have isolated a fair portion of the coolant that's normally circulating through the heater, so therefore there is less coolant in the engine and radiator and that less amount of coolant can be heated up a few more degrees.

Smee
I never tried turning the heater off when i was getting the 68/69 but after the new stat the heating is still set the same and i am getting 89/91 ??????????

Have faith Smee, it's Christmas, Santa will bring a working thermostat and all will be well.

i had the split expansion tank and had to replace it at the bottom of the expansion tank bracket is where part number 4 sits in and goes up inside the expansion tank and is only used on auto vehicles and beware if you have an auto and have to replace the expansion tank these little thermostats usually break when you remove the old tank.