Couple of theories on the diesel cool running problem?

[T-Cut]

Originally Posted by clf

I am not sure I understand what you mean by 'that is the answer'? You think there may be coolant leaking through the in line stat?

That's the proposition. If the elbow into the radiator top is hot, then hot coolant is flowing into it. If not that, then by conduction of heat via the in-line stat. From what you've described about the temperature at the elbow, simple heat conduction seems an unlikely explanation. The slightest flow of coolant into the radiator will radically reduce the running temperature. We know the flow through a 1/8" bleed hole is sufficient to give a low running temperture.

If the weather holds out tomorrow, I will try to get the spare stat and replace. Before that, I will fit it with the hose off the car and fill with water, to see what happens.

It will be informative to know if the R5 stat is water tight.

TC

[clf]

That could be an explanation (the water tightness of the disk). Hopefully I will get good enough weather tomorrow to try it. I dont have a covered workspace. After three stats, it will be good to get some form of resolution. My theory relies on the stat being fully functional, and the coolant actually reaching 88 degrees (or similar) just the sensor under reading by 10 degrees.

I havent read of it happening before. But the sensors are getting on a bit now, so in my head it is feasible failure item.

I do appreciate everyone taking the time to discuss this.

[daznkel]

Given my own recent experience with the 89deg R5 stat (not drilled/modified in any way), albeit within the last few days. The engine reaches temperature ok and the stat cycles just fine now.

However, even if there were some leakage past the "metal to metal" mating faces of the stat, I really do not think it would be responsible for such a significant drop in the MPG figures. Akin to the ambient temperature dropping by say 5deg, the MPG will drop, say 2-3MPG, not 10 or more!

What is significant for me, is that the top hose is "hot to the touch", this is the case with mine now. The stat is clearly doing its job and purging hot coolant to the radiator for cooling.

So why the significant drop in MPG figures?

As I said in my own post, I will present "normal" figures for myself next week with the new stat fitted and this can be compared to the 35-38 MPG I was getting.

However, early indications are, that although things have improved, I will still not be running at 35-38 MPG!

[HarryM1BYT]

Originally Posted by clf

lol I dont think it closing would be an issue, but I still wouldnt take the chance. I have never heard of the bellows type, so looked them up.

The bellows type preceded the wax type, upto the 1960's. I think they used alcohol as the expansion medium, so they needed to be a larger volume. They tended to leak the alcohol out which would cause them to fail closed. Wax stats were sold as an after market option, as a more expensive, but more reliable unit which failed safe (failed open).

[murphyv310]

Originally Posted by clf

lol I dont think it closing would be an issue, but I still wouldnt take the chance. I have never heard of the bellows type, so looked them up. The E-Type jag seemed to use them. (E-Type Jag inline stat mod sounds better than the R5 inline stat mod lol)

I certainly wouldn't discount a bellows thermostat. The Waxstat's fitted to our cars are far from reliable, whether in the Diesels or Petrol models.
Bellows thermostats are old technology dating back to the 19th century. There are advantages and of course disadvantages with them for automotive use.
The advantages are they can be very accurately set for opening and closing temperatures, they can open much wider due to the construction, wax thermostats are limited as to opening and tend to be sluggish in operation which can cause the pulsing we see on the OBD or on other cars with proper gauges.
Their main disadvantage is they fail closed. TBH probably no worse than the failed closed thermostats in the KV6 engine.

Over the years I had many cars with bellows thermostats and never replaced one!
The Skoda MB & S series used a bellows thermostat the later "Estelle" used a wax type and the Estelle had far more cooling issues than the earlier models.
I'd also think that the body of the bellows type would be a better idea as it will be closer to the bypass.

Here is a Skoda 1000mb thermostat for perusal
http://i.ebayimg.com/00/s/MTYwMFgxMjAw/$%28KGrHqF,!lcE6htclz4KBOtDbJmImQ~~60_1.JPG

[T-Cut]

There's no 'fail safe' design of engine thermostat. The only guaranteed 'fail open' stat is the latching design, which locks open if the coolant overheats excessively. The stat itself doesn't fail but has to be replaced. The MGR stats aren't of this type and the 'failure' of the diesel stat doesn't prevent its operation. It eventually opens over a lower temperature range. This is apparently caused by a change in the characteristics of the expansion wax. When stat failure is discussed, the actual cause of the failure is not. Other than the diesel, we don't actually know what 'fails'. The usual cause, I suspect, is deformation of the piston seal, resulting in wax loss/coolant ingress. When coolant enters the capsule (during the cooling phase), the valve stays partly open due to loss of volume for retracting the piston. This must be an important cause since there are Patents issued on preventing it. Another known cause (of PRTs failure for example) is the effect of engine oil in the coolant (from HGF or HG leakage). The primary valve in the PRT (like the OEM diesel stat) has a rubber edge seal. Oil contamination causes this to swell and detach from the valve. This then leaks coolant through or is wedged open by the detached rubber. If the current problem is indeed due to some failure of an R5 stat, it can only be explained if it's examined closely. Unfortunately, that's a tedious process

TC

[Ps3000]

The electric thermostats on BMs seem like a good idea - but they seem to have a poor rep -

http://blog.bavauto.com/3462/bmw-ele...ne-thermostat/

[T-Cut]

Just a thought. Somewhere related to this thread, I saw some photos of an R5 stat being replaced. Can't recall where they are, anyone got the link?

If not, has anyone got detailed photos of the R5 stat? I think it might be useful to post them here.

TC

[Heddy]

Originally Posted by T-Cut

Just a thought. Somewhere related to this thread, I saw some photos of an R5 stat being replaced. Can't recall where they are, anyone got the link?

If not, has anyone got detailed photos of the R5 stat? I think it might be useful to post them here.

TC

There's this , courtesy of Jules
http://www.the75andztclub.co.uk/foru...89&postcount=1

[clf]

Originally Posted by T-Cut

Just a thought. Somewhere related to this thread, I saw some photos of an R5 stat being replaced. Can't recall where they are, anyone got the link?

If not, has anyone got detailed photos of the R5 stat? I think it might be useful to post them here.

TC

I have some pictures of my stat being fitted, but my phone won't allow me to post. Later when I get home, I will get the stat out of the shed and get some pictures.

Where do you want the shots of? Is there anywhere in particular? Obviously the disc will be one.