Temperature gauge anomaly

[Liam7755]

So, don't shoot me down if this is simply quite normal .. I cant say I've noticed it before in any of my motors but for some reason when I go down a large hill .. like on a motorway or dual carriageway my temperature gauge drops from approx 88/90 degrees down to 75/80 degrees .. so approximately drops 10 degrees quite quickly, id say within 15 seconds of driving down the said hill in question. Is that normal?

 

[rf065]

All of mine have always reached temp & stayed there regardless. Have you checked the levels?

 

[Stratman]

It sounds like the thermostat is on the way out, quite a common failing on MB engines.

 

[Tonygw]

The OM651 has a mapped thermostat meaning the thermostat operates depending on engine load, ambient temp, engine speed etc.

Mine fluctuates between 80 and 90C. If say I drive 100miles of motorway the temp often stays around 90, once off and onto a a or B road the temp will drop sometimes as low as 80C for a while and then return to 90C depending on road conditions.

If I drive steadily for a while the temp stays rock solid, if I give a sudden burst of acceleration the temp will drop. its something to do with efficiency of cooling etc and perfectly normal.

Its a very clever system and helps with MPG and efficient running.. Its not faulty and its not a failed thermostat.

Mines been this way for the last 5 years.

 

[Stratman]

^^^^That's progress for you