W116 6.9 vacum advance temperatur switch

[ramiro]

Hello,
As i am still not satisfied with my engine temp on the german highway i found the attached note in the manual.
It states that some cars had a valve to disable vacum advancing when the engine is hotter then 90 C , i find it very odd that there is no mention on which cars and for what reason , most likely to reduce engine temperature ?

I am pretty sure that when driving constantly at 180 - 200 kph the vacum advance is active because you need very little throttle input for that also i can see on my AFR gauge that the wot enrichment is also not active , it really only comes on above 220.

So maybe they only installed this valve on cars that were pushed and had complains ?

[Randys01]

The photo depicts a V8 with K jetronic..so that limits the scope.
The arrows point to the distributor  port that ordinarily connects to the vacuum valve on the firewall to increase the advance when the a/con is switched on.

I cannot see what the other arrow is indicating. I cannot read German so it's a bit hard !
but the gizmo /temp control sender seems unique.I've not come across this before.

Why they need to do this seems crazy coz if ever a car was going to run hot at hi speed it would have to be Australia and they are not fitted to 6.9's at least !
The article you are referencing appears to be a full service manual extract..ie .it is not a "bulletin amendment?"

Let's see what else presents!

[ramiro]

The picture clearly shows an 6.9 Engine.
The screenshot is directly from the 6.9 section in the service manual it is also the only engine where this is mentioned.
I would translate the text but it only says that this switch disconnects the vacum advance above 90 C engine temperature , sadly i was not able to find a part number for this exact switch only 1 with 63 C but without the vent hole.

Maybe because in australia there was no legal way to drive > 110 constantly ?

[andrewk]

The picture clearly shows an 6.9 Engine.
The screenshot is directly from the 6.9 section in the service manual it is also the only engine where this is mentioned.
I would translate the text but it only says that this switch disconnects the vacum advance above 90 C engine temperature , sadly i was not able to find a part number for this exact switch only 1 with 63 C but without the vent hole.

Maybe because in australia there was no legal way to drive > 110 constantly ?

The Australian spec motor is different to the Euro spec motor.

Essentially, lower compression ratio and a post combustion air injection system, with Pierburg valve on exhaust for recirculation of exhaust gases to lower emissions. Similar to the USA version but with some slight differences.

However, there is still a valve for this purpose. On my car this was broken (plastic fittings snapped) and the air pump had already been deleted. EGR valve likely failed but the intake was completely full of Carbon junk. So, with the intake manifold replacement I have also fully deleted the EGR system and associated valves.
I am not sure if I need to also bypass the vacuum dashpot mounted on the fire wall.

It is a mystery as I will need to do testing once the last stages of re-assembly are completed.

[ramiro]

I actually found out on which cars it was installed , it was for the early Europe Engines that had 8.8 compression ,on those engines they had trouble with headgaskets so Mercedes later reduced the compression to 8.6 and then 8.4 in europe , and wrote in the workshop manual that this valve should be fitted to the engines with 8.8 compression to prevent headgasket failures.

[Randys01]

Very good thanks.....

[raueda1]

I actually found out on which cars it was installed , it was for the early Europe Engines that had 8.8 compression ,on those engines they had trouble with headgaskets so Mercedes later reduced the compression to 8.6 and then 8.4 in europe , and wrote in the workshop manual that this valve should be fitted to the engines with 8.8 compression to prevent headgasket failures.

This compression story is an interesting point that seems to be lreally off the radar.  My car is a 1976 Euro build (pretty early) and lacks that valve. During the rebuild process after my bent rod episode, I discovered that the engine had previously been rebuilt. The new pistons either 8.6 or 8.4, can't recall now. Doing all that certainly cost somebody a lot of $$$.  Maybe the car blew a gasket and they fixed the root cause (8.?  Anyway, it's interesting that everybody cites the euro 8.8 compression, but nobody seems to know that that most euro 6.9s aren't 8.8 at all. Cheers,