Instrument Cluster replacement work around.... - PeachParts Mercedes-Benz Forum

Rustyh · #1 07-15-2015, 12:27 PM

Issue is with my DD. 91 350 SDL. 180,000 miles.

Runs really well but I am anxious about recent issues.

Is there a way to install an alternate method/ device to monitor the engine temp and the oil pressure.

I have read the thread on the arduino bluetooth instrument cluster project. It is outside my skill set at this time.

Back Story -
Replaced the fan clutch when I bought car as it ran hotter than I liked. Still hot. Swapped radiator with a flushed one from donor car and engine ran cooler.

A few months ago the temp gauge went nuts and started fluctuating. A lot. Settled down after a few weeks and now seems to read a bit low. Mechanic checked temps and recommends replacing the cluster with the one from my donor 350. We are waiting for the right moment to do this.

So a couple of weeks ago the oil pressure just dropped when I was coming off the highway. Like down to below 1. Normally is pinned on 3 under load and drops to between 2 and 1 at idle.

Drove straight to my shop and had it looked at.

Mechanic seemed ok with the issue and thinks it is the sending unit. He looked in the valve cover and observed a satisfactory amount of oil pumping. Said to relax. We will address sending unit at next service.

Can the two reading issues be related to dirty and tired gauges? I hope so..........

I also have a very small leak in my water pump which we will replace next service. Not having confidence in the gauge, this issue makes me more nervous.

So finally the question..........

Is there a way to install an alternate method/ device to monitor the engine temp and the oil pressure.

This would extend the time to replace the instrument cluster gauges. It will also give me more peace of mind in general.

Secondary question would be where does one refurbish an instrument cluster?

As usual any and all suggestions are appreciated.
Rusty

Nate Stanley · #2 07-15-2015, 01:03 PM

This appears to be more of a problem with the instrument panel grounding..for the temp gauge and oil (which has an electric sender)gauge to both be bouncing around, it might be time to pull the instrument cluster and look for bad/corroded ground connections.

25+ years is hard on a car, but with proper connectivity there should be no need to mess with Bluetooth setups. My old '84 300D had perfect gauge reliability right up to the time I sold it 4 years ago.

Jeremy5848 · #3 07-15-2015, 01:21 PM

The gauges themselves are usually quite reliable but connections in the cluster can oxidize over the years and cause problems. A separate issue is the senders, which are usually the first thing to look at when there is a problem. I have replaced a couple of them in my cars over the years.

I know of no one who refurnishes instrument clusters as a business. You can definitely buy separate instruments; I recommend VDO but there are many brands. The trick is to find a sender that fits the existing threads in your engine.

Jeremy

Rustyh · #4 07-15-2015, 01:50 PM

Gentlemen,

Thank you for the advice.

I will make sure we investigate the ground connection angle before we start replacing the cluster.

Now that you mention it I am remembering something about grounds from my mechanic.

I have driven MB diesels since 1976 and this is the first gauge issue I have encountered. I guess they are pretty reliable.

Thanks,

Partscarver · #5 07-15-2015, 03:04 PM

Sending units fail, either the resistor winding wears through or the flat o ring ruptures
and fills the unit with oil.

Rustyh · #6 07-27-2015, 08:31 AM

I have been thinking on the ground issue and how it impacts the problem. I have not addressed it yet but will soon.

Does a poor ground cause the reading from a sensor to report less than the intended reading?

I am thinking that a sensor has a positive feed side and a return side that is connected to a gauge. The gauge effectively reports the ratio of the sensor reading to 100% of the supplied power source.

Is that how these work?

Thanks,
Rusty

Maxbumpo · #7 07-27-2015, 09:42 AM

A poor ground can cause either high or low readings, depending on the particular circuit involved. The poor ground may cause the instrument cluster to find another path to ground, which may go through a gauge and cause the gauge to read high, or the ground path may go through a different circuit. This is very hard to predict.

Another common source of electrical gremlins are the fuses, and specifically corrosion and aging of the fuses. If you have never replaced ALL the fuses, that is a simple and relatively cheap way to eliminate a source of gremlins. Please get the proper copper fuses, and rotate each a bit once inserted to get a better connection. If you have time, clean up each fuse mounting connection with a pencil eraser prior to installing.