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1997 SL500 - VIN WDBFA67F8VF151031 and 2011 E350
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70 Posts
Discussion Starter #1
My recently purchased 1997 SL500 occasionally shows zero oil pressure on the analog gauge at idle (e.g., at a stop light), but usually the pressure is 1.5 to 2.5 at idle. The oil warning light illuminates properly when I first turn the ignition on, but goes out properly as soon as I start the engine; I have never seen it illuminated while I am driving. Can somebody clarify whether this suggests an oil pump problem? Is the oil pump an electric pump, or a typical mechanical pump that runs off a pulley driven by the serpentine belt. Is the red light an oil level indicator, or a pressure warning indicator?
 

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2000 SL320, 2001 CLK320
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2,364 Posts
Giive us history to work on! What is the current mileage, when was the oil last changed etc etc

There has never been an oil pump that runs off a serpentine belt - you need to educate yourself somewhat on this forum - plenty of information here.
 

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1997 SL500 - VIN WDBFA67F8VF151031 and 2011 E350
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70 Posts
Discussion Starter #3
The car has 53,000 miles, and the oil (Mobil 1) was changed approx. 9 mos. ago (less than 2000 miles ago). I should have said, "Is the oil pump a typical internal mechanical pump, or is it atypical, e.g., an electric pump or one that is driven by the serpentine belt?" It seems intuitive to me that the pump should show consistent pressure at 500-1000 rpm instead 2-4 sometime and 0 at other times, especially since the synthetic oil should have relatively constant viscosity regardless of temperature. The question whether the indicator light represents oil pressure or oil level should not be dependent on the mileage on the vehicle.

I apologize for asking questions that may already answered elsewhere on this website. And I realize that there is 'plenty of information here'. I have read a lot of info here and have tried to research the issue carefully , but was unable to find answers to my specific questions. I have also tried to educate myself more than 'somewhat' on this forum, and have been successful in finding answers to many issues. I don't understand why rorypff seems a bit upset that a 'Junior Member' should ask a couple legitimate questions.
 

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1996 SL500, 2000 E430
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3,631 Posts
I have been running "Mercedes" oil, which I was told is Mobil 1 5w-40. I have noticed with our extreme summer heat (sometimes 107F or 41C) the needle at idle and operating temp (90C) is darn near at 0.

Maybe 2mm Up at idle (stop). Once I get going it will go to 3 at 2,000 RPM or so. The Mobil 1 10W-40 I used to run was pretty similar.

The heat affects this too as in winter it idles higher. Much closer to 1 bar.

What is the viscosity? As long as it is going up to 3 bar at 2,000-2,500 RPM I would say don't worry about it.
 

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1999 SL600 (67k miles), 1998 SL500 (sold, owned from 67k-91k miles)
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112 Posts
Your oil pressure sender might need to be replaced, but I doubt there's any issue beyond that. This gauge was removed altogether with the '99 refresh, I suspect because it was unnecessarily worrying people. Those of us with '99+ models are blissfully unaware of what our oil pressure is at any given moment. I had similar symptoms with my old '98 -- pressure dropping to zero in hot conditions at a stop -- and had the sender replaced, and it no longer zeroed out after that, so it may be worth the (modest, as I recall) cost for peace of mind.
 

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2007 CL600, 2003 SL55AMG, 1987 560SEL ECE, 1985 280SL
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1,519 Posts
The oil pump is internal and chain driven. It is rarely a problem part on these engines, pretty close to bullet proof. Check your oil level and if it's fine I agree with the others that your gauge might be a tad off and that the warm weather will further drop the displayed pressure. The most important is to check that the pressure is max when accelerating.
 

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1997 SL-500; 2002 ML 500 sold; 1999 ML 320 sold; 2003 E 500 Sport sold
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235 Posts
Had the same issue, below 1 bar when water temp nearing 100 at idle then fine when rpm increased. Changed the sender and resolved the issue. These engines are pretty bulletproof and especially a low mileage one like yours if they have a decent service history. I use Castrol Edge 5-40 oil.
 

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1997 SL500 - VIN WDBFA67F8VF151031 and 2011 E350
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70 Posts
Discussion Starter #8
Thanks for all the useful replies. I am concerned about oil pressure indicators because I once had a Ford F150 which I thought was a true oil pressure indicator. However, I found out that the 'gauge' was only triggered by on-off sender from the engine. I ended up coasting into a Ford dealership 500 miles from home with zero oil pressure and a rattling engine on a holiday weekend, and I ended up buying a new truck to continue my trip. If the original truck had been equipped with a true oil-pressure indicator, I might have noticed a gradual degradation in oil pressure to warn me weeks or months in advance that the oil pump was heading for failure. It's shameful that even Mercedes decided to save a couple bucks on newer models than mine by eliminating a true oil pressure indicator.

My conclusion is that the analog gauge is a convenient oil pressure indicator and that if the indicator light comes it means "We're all gonna die very soon".
I typically show oil pressure 3-4 on acceleration or at engine speeds above 1700. I don't know the viscosity of my oil. Maintenance records from the previous owner indicate that the oil was changed by a reputable shop in FL in December 2016. The oil is very clean (about 2000 miles later). I believe that the shop I use recommends 5W-40 for my 2011 E350 here in Dallas TX. I suspect that similar oil is in this 1997 SL500.
 

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1996 SL500, 2000 E430
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3,631 Posts
As long as the pressure is going significantly up when you rev I think you are fine. Synthetic oil, particularly the lower viscosities, is very thin but it is protecting those parts under extreme heat.
 

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1996 SL500, 2000 E430
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Yesterday when it was 104 and my coolant temperature was 100° C the needle was just a hair above zero maybe two or 3 mm? Now I just started the car at 86° outside air temperature and it's above one bar

I'll bet yours would be the same upon start up
 

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1992 R129 500SL
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25 Posts
Change the sender and don't keep to much attention to the readings :)
I had three senders and every had a different reading - not much, but around 0,5 of difference, between new pieces...
 

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R129 500 SL 1991
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950 Posts
My recently purchased 1997 SL500 occasionally shows zero oil pressure on the analog gauge at idle...
There are lots of potential causes of a low oil pressure reading on the gauge at idle.

The oil pressure gauge and warning light are controlled by a microprocessor in the instrument cluster, which compares the resistance value from the oil pressure sender at the base of the oil filter and the engine speed (rpm). The warning light operates if the oil pressure drops below a certain value for an engine speed >1200 +/-60 rpm. At idle (~700rpm) the threshold for the warning lighting on the characteristic curve in the processor is very low, so that the warning light would not normally illuminate at idle even though the needle is close to zero.

Note that there is a separate oil level sensor, which is related to a separate warning light on the bottom of the instrument cluster.

First step would be to do the simple check of the viscosity of oil for the ambient conditions. But given you say that the gauge normally reads 1.5 to 2.5 bar at idle, you could probably rule out oil viscosity.

Next step: - Observation. Note the way the gauge needle behaves. Is it smooth or erratic?

If the needle slowly drops to zero, you could eliminate a faulty gauge. With faulty gauges the needle tends to flick to 0, or flick back to reading if it is intermittent.

Next step: - Check the resistance at the sender. With engine running, when the fault presents itself, unplug the connector at the sender and check the resistance at sender. If the resistance is zero ohms (short) or infinity (open), replace the sender. As it is intermittent it may be simpler to replace the sender anyway.

Next step: - Check the wiring and connectors to the sender unit and to the back of the instrument cluster. The oil pressure pointer will slowly drop to zero if there is an open circuit in the wiring between sender and cluster, or between cluster PCB and gauge, or a faulty cluster PCB. Note the warning light would not come on in this instance.

Voltage is supplied to the instrument cluster through the ignition lock, (fuse no. #? in the fuse box). The electrical contacts in R129 ignition locks are a known issue with a high failure rate, causing electrical anomalies in the cluster and also difficulty starting when problem becomes critical. Early signs may be erratic behaviour of cluster lights and gauges. Try wiggling the ignition key and moving the steering wheel fully up and down a few times to see if this makes a difference.

Next, remove the instrument cluster, open it up and check/clean the contacts at the back of the gauge. To do this you would need to remove the front instrument bezel to gain access to the gauges, remove three screws around the gauge and withdraw the gauge.

Next would be to check the pressure relief valve. If it is slightly stuck open this could cause very low (zero) pressure at idle, but normal pressure when you increase the revs. Do your lifters tick at idle? if yes, drain the engine oil and drop the oil sump pan and check for any debris/fragments from the timing chain tensioners in the bottom of the pan. If you find anything like small black plastic bits in the sump, it is likely that these could also have got in to the pressure relief valve, causing it to stick open. Remove, clean and reassemble. Try to identify source of broken fragments. Check plastic timing chain tensioners / oiler tubes and replace as necessary.
 

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94 SL320 98 SL500 99 SL600
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I have a 98 SL500 that I got at 52K It did the almost zero at idle when hot but 3 at 2000 RPM scared the hell out of me so I change the sender and that helped some, but still had low idle readings between above 0 and closer to 1. I live in So Cal and drive a lot of desert roads WOT so my oil is GTX 20/50 so far miles are at 74K and no issues I was told that they had complaints about this and as stated earlier did away with the pressure gauge and replaced it with a oil temperature gauge. I have a 99 SL600 that uses the temperature gauge that will match the coolant gauge at operating temps.
 

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2000 SL320, 2001 CLK320
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Thank goodness mine doesn't have an oil pressure gauge, its bad enough continually having to look at the speedometer.:smile
 

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1996 SL500, 2000 E430
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3,631 Posts
Thank goodness mine doesn't have an oil pressure gauge, its bad enough continually having to look at the speedometer.:smile
I was goinkg to change the oil in my mothers W210 and was reading up on it. To me I have always watched either an idiot light - low oil pressure - or a gauge insuring that the new oil is up - and this is a new thing for me. I guess if the engine doesn't seize you know it worked out OK?
 

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2000 SL320, 2001 CLK320
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2,364 Posts
When last did you hear of a Mercedes engine seizing up due to no oil pressure?

I would say technology has advanced somewhat.
 

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1996 SL500, 2000 E430
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When last did you hear of a Mercedes engine seizing up due to no oil pressure?

I would say technology has advanced somewhat.
All depends on, of course, the oil pump. But to my point: An old master mechanic told me to not be distracted in the middle of a task. If you have to add oil to an empty crankcase, don't be distracted by a phone call before.

Say you start a W210 with no oil. Would the check engine light go on?

I don't know.

I have after almost 20 years of Mercedes ownership (and taking care of my parents Mercedes(es) for 20 years before that) - having the comfort of watching that oil pressure needle after a second/2 rise after an oil change. In the case of my mothers 280SL Pagoda - the oil pressure seemed to rise very uncomfortably - I look under and oil is gushing out of the canister oil filter. I had forgotten to remove the old O-Ring before installing the new one.

I suspect though most people don't know what to make of the gauge which is why it is gone - as the dipstick, i am told.
 

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R129 500 SL 1991
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950 Posts
Here is the same car an hour later at 97° and a hotter engine
Your gauge readings appear to be consistent with the grade of oil you are running. :)

Where is the CEL on your model? Can't see it in the photo.

On mine ('91 500SL) it's just above the speedo pointer.

Regards
Rob
 

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1997 SL600 Brilliant Silver Sport with grey/dark metal interior, 234K miles
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Mineral 10W40 is spec'd for my 97 SL600.

Getting the 11 quarts plus filter changed at the dealership for $50 is a modern day miracle. The only time my oil (hot or cold) somewhat dips below 2 on the gauge at idle, is when synthetic oil is mistakenly used. It's quite obvious and occurs often enough so that I now tell the service manager before maintenance to be SURE to use mineral based oil or they will immediately have to drain and refill.

Even with cold new synthetic oil, the gauge reads around 2 at idle instead of a solid 3. I don't use the synthetic because my engine seals were conditioned with mineral and after 250K miles, I don't want to have to replace them due to swelling.

Your 97 should be spec'd for mineral 10W40. It's no wonder MB switched from a pressure gauge to oil temperature right at the time they went from mineral to synthetic specifications.

I put synthetic oil in the same category as platinum plugs, just don't.
 
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