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Discussion Starter #1
Been driving me nuts. Sounds like someone in the glove box thumping once every minute or so. Finally tracked it down to a solenoid valve that sits below the heater motors under the bonnet,can hear a click from relay just beforehand . Noticed the little cylindrical actuator was hot. Only way to stop it is to turn off heater. Any ideas? Valve? sensor? heater printed circuit under transmission tunnel?
 

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There was a kit before I think, maybe still available.
Replace coolant too
 

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Discussion Starter #7
Took the valve out. Had to take out heater fan first.Bench tested it an it actuates and doesn't click on off every minute like in car. Took it apart and seals do look poor.So I am wondering if some sensor is dodgy but in reality this will be a process of elimination. This is a Bosch unit but no Internet trace as a Bosch part except Ferrari .Flying Spares only sell used ones and Introcar have no stock. I have put enquiries in but suspect this will be another one of those extortionate parts that have been made hard to find even though generic certainly in the UK. Looks like mines an early one and possibly a later one might fit. I wonder iff one from another model migt do. Does anyone know which relay controles it. To be continued.
 

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Discussion Starter #9

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Discussion Starter #10
Got new internals from Introcar OEM part about £90. Easy change. Still permanently opens and closes every minute or so but no clunking noise as seals are new. Will see if this also happens on other car as a comparison.
 

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This is a common repair for any Mercedes Benz from the early 80's to the early 90's and the part # is 0008350644
The issue in recent years is that quality manufacturers like Bosch and Mercedes Benz supplied parts are no longer available. What you do get these days is the MTC and URO part brands which in most cases, the diaphragm will fail within a few weeks or months.

I'm hearing that the MB part is back in production, if so, buy a couple and put them on the shelf. I also know of several people who made their own diaphragm from bicycle inner tubes with good success, because the quality of the rubber is better.

Here's the link which describes how to do it: Mono valve home made diaphragm replacement DIY - PeachParts Mercedes-Benz Forum
 

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Discussion Starter #12
I think the issue in my case is a signalling one from one of the sensors as the whole valve including diaphram is new. Open valve/close valve/warm enough/more heat etc. Without the weird factory heater analyser I think I'm stuffed. When I use my Turbo R I will see if it is also doing it ie. on/off every minute. System is well bled. Has anyone noticed that when you take the expansion cap off even when warm there's no pressure in the system. Cap is new and tests fine in my pressure tester. Is this normal?
 

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How hot is your engine when you remove the cap? If it's at around 80 degrees c , then there should be some expansion.
 

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Adamski, have you cleaned the AC microprocessor circuit board connectors with de-oxit? My 89 had some issues that stopped once I cleaned the connectors.
 

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Discussion Starter #15
I am replying to the two previous comments. Engine appears to be warm but I can't check temperature with my laser as we're all grounded but both engine and cap pass pressure test so I do find it strange. Maybe cooling system is over engineered. Must say temperature gauges only move about a quarter. Perhaps another pre engine management Conti/Turbo R owner might loosen cap carefully with glove and rag when warm and see if there's pressure.

Regarding the AC circuit board-where is it? I suspect it was repaired when heater matrix was replaced and might be as you say. Is it somewhere under the centre console/tunnel rings a bell??
 

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I can only vouch for my 89, but suspect it is very similar on your car. The AC control board is under the center console, directly below the servos. There is a printed circuit connector on either side of the board, clean both of these.
The heater solenoid circuit is, from PCB right hand side, purple/orange wire to Water Tap Relay which in turn activates the water tap via wire red/brown. There are tho separate grounds in this circuit, one on the transmission hump that grounds the circuit board, the other one is located at the front valance earth point. There is a series of 8 relays 2 x 4 under the bonnet, the heater tap relay is the forward left relay of this group.
Again this is the configuration of my 89 Spur, your car may be a bit different, but this system started in late 87 and Rolls usually carried there systems over for several years.

Hope this helps.
Jim
 

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Discussion Starter #17
I thought I would give the forum an update. I did change the valve/tap internal. Yes the seal and plunger diaphram was torn. New valve is not available. Sadly this did not help. Still 'I hear you knocking. So I did remove the heater control panel deep in the bowels of the footwell and sent it off to Bowlings. Two weeks later I'm told there's naught wrong with it,its your valve!. Apparently the original BMW valve isn't up to the job and the solenoid can't take the pressure Captain.
I was told leave out the valve internals. So will advise of final conclusion. At least some other victim will have the benefit of my experience.
20200805_124754.jpg
 

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Check the Mercedes Benz forums. I remember reading somewhere that someone made a repair diaphragm from a bicycle inner tube. If so, I suspect that it will last forever.

edit: and here we go

 

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Discussion Starter #19
I did fit new factory internals which includes new diaphram. The issue aparantly is the valve solenoid becomes too weak and can't hold back the flow and subsequently a clunk repeated never ending.. I'm going to remove the internals of the old one effectively causing the valve to be permanently open.I'm told the effect is slightly longer warm up in theory and internal heater flaps control the actual warm air into cabin. Anyone experienced this? Apparently its common.
 

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Discussion Starter #20
Got the heater circuit board back fully checked with no faults. Valve still knocking.Removed the valve and refitted the old internals suitably cropped with no shut off piston bit. Valve is now open flow.Plunger still knocking om/off so disconnected the wire connection to valve.So the valve effectively is always open but it does have a non return floating ball valve so it still has a function.I was told the electro magnet no longer has the strength and this is commonly done. The only way to make a final conclusion is to replace the complete valve and if an opportunity arises to purchase one I will.
At least no more knocking now like the scene in Goodfellas when Frank Vincent/Billy Batts was in the boot, Drove me nuts:LOL:
 
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