I my old life before moving to France I was a Senior Project Engineer for a Automotive supplier and designed cooling systems for cars and trucks etc. Having spent many days in wind tunnels like MIRA and hot climate testing in Death Valley I was curious to see what temperature the oil is on an air cooled engine. Just fitted a temperature sensor to a new sump plug and run the car in 9 deg ambient - bulk oil temp only 50 deg C at road speed 90 kph (without grill guard). With grill guard the oil raises to around 65 de C. Also with grill guard the flat spot between 1st choke and second choke disappears.
Think I will be running car with grill guard to higher ambient temperature than the 10 deg C stated to make the engine work more efficiently.
Thoughts PLEASE

Seems low, have you tested the sensor+gauge in boiling water?
Believe ideal temp for oil is > 80 Deg C

have you got an under tray like it was supposed to have? type of oils have a bearing on temp IIRC synth runs cooler


so between 10c and 15c its a kind of hinterland according to the handbook

Have undertray fitted with sealed small bulge for the sensor. Also when stopped checked the dip stick temp with surface temperature gauge (instant read type) and gauge is working fine. With water cooled engine the oil is normally higher than the water - around 100 - 105 deg C but with air cooled there is no water jacket to heat the block.

Dyane61976,
I've always left the grille muff in place on our Dyanes until the ambient temperature is above 15*C.

No adverse effects noted over the last 32 years and engine in the old grey shed is well on the way to 250,000 miles...

The oil in an A series engine will be at its highest temperature when it's in the rocker covers, I'd have thought, as it will just have passed through those galleries surrounding the exhaust valve guides.

Ken.

( If there's any sign of 'mayo' in the filler/breather neck, that's a sure sign of an engine running too cold.
On one car I serviced, I had to clear the filler out with a teaspoon to uncover and remove the plastic mesh.
I've even heard owners saying that they have to run without the muff in winter to stop the engine pinking, when it would make much more sense to set the ignition correctly. )

Chris Stuart oz raider and found on Yahoo's 2cv-L did a lot about oil temperatures in his 2cv I haven't got a copy of it but im sure its out there somewhere. I think given the relative size of the finned sump the reading was low there - the oil filter sandwich plate being chosen as the best as it measures the temp of the oil being fed to the bearings. Highest oil temp will be at the exhaust valve guide where it then goes to rocker box and back to sump via the pushrod tubes - getting cooler at each stage.

sign up to 2cv l and search out the myriad of oil and engine temp threads - it does get a bit anal on there with endless theoretical discussions about airflow over fan housing flanges or such like

EDIT ha ken in there too while id been sent off to do something "useful" like getting milk from the co-op

Years ago, I had an oil temp gauge on a Mehari that I used as my daily car. I, too, thought that the sump plug was a really good place to put the sender.

It wasn't. It was, quite frankly, about the worst possible place.

Not only was the reading utterly irrelevant - to the point where the gauge rarely got off the 50degC stop - but it was incredibly vulnerable, since it hung below the undertray. Fortunately, not one of the three senders I mashed before I gave up on the idea caused all the oil to leak out. But it was close.

Sean - I think the 10-15degC gap is deliberate, to stop the anal wasting entire spring/autumn days checking their thermometer constantly and stopping every mile or two for muff-swappage.

matron

So it appears that the start of the oils journey the temperature is quite low and even when it returns via heads etc the extra heat is not enough to heat the mass of the oil above its original temp. No wonder I have read somewhere that Citroen to prove the engine ran them on test beds at full throttle for 1000 hours continous (about 50,000 miles flat out) The oil cooler along with forced air does enough to keep the oil at low temp. Time to remove sensor and gauge.....

see the more you get into them the better they become