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Oil pressure sender, idiot light and instrument

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9.9K views 18 replies 9 participants last post by  LeonardoDaBenz  
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#1 ·
Hello, all

I have recently aquired a nice SLK200K, and to my (manageable) dismay, find that there is a oil LEVEL indicator, but not even a pressure idiot light nor pressure instrument. (The latter was obvios from the start, of course). Now, I want to add at least a pressure sensing switch (and a idiot light) or even better, a pressure gauge.

The official handbook use a method where a modified filter canister top is connected to a manometer to check on oil pressure. OTOH, I know that Mercedes have had oil pressure senders in the olden days, and suspect that there might be a plugged tap somewhere in the oil line.

So, first question: Is there a plugged access to a suitable oil pressure gallery for a pressure sender/switch?

Second question: If there is no suitable plug or outlet already, I might go the route of the mechanics, and add a sender to the canister top of the oil filter. However, the factory manual says to remove the filter, and that may have to do with the filter (if it's in place) messing up the actual pressure reading. I would like comments on this approach - is it doable at all ?

Comments (even "dont bother, this is why..." are much appreciated.
 
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#3 ·
This is the very first car I have owned that didn't even have an Idiot Light at least. I sure would like to know what the pressure is, as a car ages, it gives you a fair estimation of your bearings, as bearings wear, oil pressure drops over time. For me, an indicator of when an engine needs a rebuild is hot vs. cold oil pressure. My HD has a light and a gauge, at 33,000 miles on the bike in the HOT Florida weather, I had to switch from a 20-50W Syn oil to a straight 60W syn oil. With the 20-50, Hot at idle, the gauge would show "0" psig, but the light would not come on, because the gauge was not as sensitive as the light that is set to trip at 5 psi. Now running 60W, at idle, pressure indicated is 10 psig.

I would HATE (and would not do it) to clutter up the dash with extra gauges, it sure would be nice to have the MFD be able to show oil pressure. Dream on I guess.:frown:
 
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#4 ·
A idiot light (low oil pressure warning light) would be easy to incorporate into the lamp set so all is not lost for us "let's keep the dash like Mercedes intended-people" - even if there is some room at the ashtray for instruments. Finding a visual match may be harder, but there are add on instruments that look very decent on images in the forum.
 
#5 ·
There's a low oil level lamp - but that only shows level. I'm not sure about oil ways you can tap into though.

I'm also told that there is some trickery on the SLK320 that reads the oil level after you turn the engine on:

First the engine must not have run in the last 5 minutes.
1) Turn the key to position 2 (engine not running).
2) After about 10 seconds, an oilcan an a clock will appear in place of the mileage display.
3) Press the left-hand button (the odometer reset button) rapidly twice in succession.
Click to expand...
I'm not sure if this is valid on a 200 or a 230 though.
 
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#6 ·
savcom said:
There's a low oil level lamp - but that only shows level. I'm not sure about oil ways you can tap into though.

I'm also told that there is some trickery on the SLK320 that reads the oil level after you turn the engine on:



I'm not sure if this is valid on a 200 or a 230 though.
Click to expand...
Low oil is signalled on my model too. What I have found is that Mercedes own Techs use a special oil filter top, with a manometer outlet (instructions for how2 do that are in my factory workshop manual) and i know there is a oilway available on the V6 engines. Also, I know that there are older 111.xxx engines (not SLK) with oil pressure senders.

I am slowly approaching some solution, even if that means drilling and tapping for a 27nptf sender (which I may or may not do, when opportunity arises).

But it woud be nice to be presented with something that is already there... :)
 
M
#8 ·
I felt the same way when I realized there was not even an idiot light and I have done what you are asking about. I have some pictures of the gauge install into the console. I will have to get some pictures of how I installed the sending unit. Mods to the console are not for the faint of heart as some cutting was required! The sending unit install was pretty straightforward. I will post pictures soon. I may also go to a mechanical gauge as the sending unit is fairly large and has to be removed to get the wrench on to change the filter.
 

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#9 ·
WoHoo! Excellent to hear this:

Is it so, that the sender is installed on top of the oil filter ? (This is, I have found in the workshop manual, how Mercedes measure oil pressure - with a dedicated device).
 
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#10 ·
Here are some pictures of how I installed the sending unit. I drilled and tapped the oil cap for a 1/8 NPT fitting, making sure I marked where it would fit. As you can see, the sending unit is rather large, hence my thinking about a mechanical gauge. I just didn't really want a pressurized oil line in the cabin. The grommet I am pointing out is in the perfect place to route the wires or oil line. It is under the dash high enough not to be seen, but reachable without removing any panels. The wiring was somewhat tricky as I had to add a stud so I could ground the sending unit. That's why in retrospect a mechanical gauge would have been easier. If you have heated seats, this gauge location WON'T work. A mount could probably be made to fit in the storage cubby. An idiot light could probably be incorporated using a simple on/off sending unit mounted the same way with the light in the warning light cluster maybe in parallel with the low oil light. (?)
 

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#12 ·
Great info.

I already have a spare oil filter top (5 bucks, used), so drilling and tapping is no problem. A low cost electric sender/instrument will suffice and removing the sender when changing oil is manageable.
I see that the tapped hole is offset, I would have thougt to drill and tap in the middle ?
 
M
#14 ·
I thought the same when I was looking to locate the unit, but the oil flows from the outside of the filter to the inside. This is not the most optimal place for the sending unit, as the filter getting dirty over time will tend to increase the pressure slightly, but not so much as to be very noticeable. I am thinking about trying to make an adapter so I can install a remote spin on type filter and put the sending unit downstream of the filter. As I am currently recovering from rotator cuff surgery, that project has been pushed back a bit. lol Where it is was the best place I found for clearance and accessibility.
 
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#18 ·
Makes complete sense. The workshop manual Points out that the "meter filter top" (which is in the middle) just works if the filter is REMOVED. I may get to work with this little project soon.

(Of course you will have a bad rotator cuff, after rotating the oil filter top on and off many times. May you heal well and quick! )
 
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#15 ·
I think my preferred option would be in the middle with the smallest sender available. I don't know how thick the filter housing is but a nut and washer on the inside would also be peace of mind. The sender would not have to be removed at oil change time but simply unplug 2 spade connectors.
 
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#17 ·
In reality, that's probably all you need. Just hook it up to the low level light in the dash. For me, I like gauges and there was the "can I do this?" challenge!:laugh:
 
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