W124 engine temperature and oil pressure

ShivaYash

Senior Member
Joined
Apr 29, 2012
Messages
558
Reaction score
12
Location
Berlin
Your Mercedes
S124 1994 E200 (M111 engine), S123 1983 230TE (M102)
Dear all,

I am still very much learning about cars so forgive this basic question.

Driving home in London traffic last night, after a weekend on A-roads, my car's engine temperature was higher than normal, and hit the 100/120 mark on the dial. The viscous fan was working and I tried increased the revs whilst waiting for 10 minutes at a temp. traffic light, thinking this would bring the engine temperature down, as the fan would be turning faster - but it did not.

The oil pressure also dropped. The oil pressure was different when in neutral compared to when in drive. Is this usual?

Now I understand that as the temperature goes up, oil becomes thinner, hence the drop in pressure. At all times pressure was back up when the engine was revved.

The car was at this 'high' temperature for about 45 minutes. Can such temperatures cook the oil and cause it to 'fail', lose efficiency, and hence need to be changed more frequently than 12 months? At present the car is serviced every April, and I follow the schedule as stipulated by MB. I always use original filters and the correct high quality oil.

I do sub 5000 miles per year, a mix of city and country driving.

Many thanks,
 
Last edited:

hotrodder

Senior Member
Joined
Oct 18, 2008
Messages
894
Reaction score
26
Your Mercedes
'93 320te, '54 ragtop beetle (in bits)
The oil pressure also dropped. The oil pressure was different when in neutral compared to when in drive. Is this usual?
Yep, oil pressure is related to both temp and rpm. Idle speed is a bit lower in D than it is in N or P. The oil pressure gauge in these only reads to 3 bar which is lower than the oil pressure is (or should be!) at higher rpm hence the gauge spends most of its time 'pegged' against the stop. Very roughly at normal operating temps oil pressure should be a min of ~1.3bar at idle, 2.2 bar at 1000rpm, and the gauge should be pegged at 3 by 1300rpm. Your owners handbook will probably state something along the lines of 0.5 bar at hot idle in gear is nothing to worry about as long as it increases immediately with rpm

Oil temps above 120C for any length of time won't do the oil any good in slow heavy traffic the oil won't be anywhere near as hot as the coolant

Are you sure the viscous fan is working properly? They always turn with the engine but when they lock up they make quite a racket due to the amount of air they shift. If you have a leccy fan(s)* in front of the rad for the aircon these should cut in or speed up above 110C as they're switched according to both aircon pressure and coolant temp. Switching points in the cooling system are here http://www.w124performance.com/service/w124CD1/Program/Engine/104/20-0020.pdf
If the cooling system is in good order and everything is working as it should be then the temp gauge shouldn't get above 100C (the line between 80 and 120) at this time of year even in a massive traffic jam. I was queuing for lights on the A20 on Fri for a good 15 mins, according to the car it was ~ 19C outside and the temp gauge crept from the usual 85ish to maybe 95ish before dropping back to 85ish again with a minute of clearing the lights

If the car gets close to overheating then cranking up the heater (and it's fan) will do a better job than increasing the rpm

* 6 pots have two of 'em, 4 pots might just have the one?
 

television

Always remembered RIP
Joined
Mar 14, 2005
Messages
164,073
Reaction score
367
Age
89
Location
Daventry
Your Mercedes
2002 SL500, 216 CL500, all fully loaded
To check the visco, the thermostat opens at 87ºC and the visco fan should speed up at 90ºC so start the car and run it up to about 70ºC by a short drive then leave it running and as the 90ºC point is reached the fan should speed up. If the rad is getting blocked, then the hot spot where the flow of hot air passes through the rad to the visco coupling will be low. At 100ºC you can feed a carrot into the fan and it should chop the carrot up, if it stops, then a new visco coupling required or the rad is blocked. In very quiet conditions you can hear the bi metal strip that fully engages the fan can be heard to click.

And yes at very low RPM the oil pressure will be lower, and worse when overheated as the oil thins.
 

WDB124066

Senior Member
Joined
Apr 13, 2009
Messages
854
Reaction score
68
Your Mercedes
1996 E320 Sportline Cabriolet X 2
^^ That right! :):)
 

AIB understand your special Mercedes deserves a special insurance policy. We have a refreshing attitude to insuring high performance, modified, imported or classic and vintage cars and deal with the UK’s leading insurers. We offer discounts for length of ownership, where the vehicle is kept overnight and limiting the mileage and can also cater for those clients who need higher mileage and business use. To obtain a quotation please call the team on 02380 268351 or visit us atAIB Insurance
Top Bottom