10 hours ago, Lofty79 said:

Just harking back to the warming up on idle debacle.

Idling from cold is a bad idea when you consider how the top of the engine is fed with oil.

From cold there is little if any oil at the top of the oilways, and the oil will have run off the components for the most part.

The engine is reliant upon oil passing up through small 2mm or so holes in the cam journal..... The cam rests on metal shims/bearings and constantly rubs on them.

Putting the engine under immediate gentle load forces oil to the top faster thus feeding these drier journals and in turn the cam lobes.

The faster this happens the better.

 

I refer to 'bed in' principles when fitting a new cam and followers for example.

These need lubricated asap and the advice is DO NOT LET THE VEHICLE IDLE! The reason being two rough surfaces grinding together needs a supply of oil fast. 20 mins or so of 2500 revs and a few hundred either way keeps it flowing.

 

Idling from cold is this principle in part, the two surfaces are mated so to speak, so less wear occurs, but idling from cold means your relying on these surfaces being mated to not wear too fast. But they are still too dry

 

Bottom line, fast idle and or immediate load (within reason) will bring oil up faster and give it more fling, lengthening the life of the motor, particularly the top end.

 

My 2p worth

This doesn’t seem to hold water to me. Good in principle, wrong in fact. Car oil systems have a fixed displacement oil pump followed by a pressure relief valve that limits the maximum pressure. With very cold oil, the pump’s delivery volume will be the same but the viscosity will be high and thus the oil flow around the system will be limited. So the oil pressure will be high even at idle and chances are, the pressure relief valve will be open at idle. Increasing the engine rpm will thus not increase the oil pressure and hence not increase the flow of oil to the top end etc.

 

All that said, I think it better to drive of gently so that the engine reaches operating temperature in a reasonable time. But just not for the reasons cited!

I can see what your saying, however on testing a vehicle after top end work, from cold. With the valve cover off, fast idle produces more oil flow than can be contained, on idle ALOT less is present.

After these practical experiments I can confirm that there is more oil at fast idle beyond any doubt whatsoever.

 

Agreed on immediate light load for shortened warm up times.

 

However a faster turning oil pump even with max pressure diversion, will pump more oil in any given direction, or, what would happen is there would be so much pressure at high revs the theoretical restriction would starve the top end of the engine.

 

Its all moot to a degree, as, only over 150k miles and 2 identical test subjects in identical conditions with identical servicing and driving styles would we ever know.

At best all we will have is theory. 

 

The only definitives are using the correct oil grade and servicing at recommended intervals or before. Also a mechanically sympathetic driving style.

Some Mechanical Engineering knowledge and training and common sense or just common sense and life experience is sometimes a help in being sympathetic to engines / vehicles and keeping ones for a decade or 2 as your keepers gives you a fair idea about starting from cold and running them in winter, if you get winters or cold weather.

 

Bl00dy cold in Blair at times.  

Edited 3 December, 20178 yr by AwaoffSki

Aye, 

Blair is a seer een fae time to time.

 

I initially thought “Blair” was a reference to Blair Atholl. Proper in the highlands! Not Blairgowrie in the Deep South Central belt!

Blairgowrie or Blair Atholl get about the same amount of weeks of cold weather payments each winter as Aboyne AB34 and DD8 postcodes.

Thank goodness it stopped being the Temps and Forecasts from Leuchars & then Dyce that were kept being used for 7 day periods.

The weather usually is milder where Airports were built and near the sea.

http://coldweatherpayments.dwp.gov.uk 

Edited 3 December, 20178 yr by AwaoffSki

Epic thread drift!

 

Latest MPG seems reasonable, although we are now into very cold weather (and low average speed commuting), so MPG inevitably takes a hit.

 

Edited 8 December, 20178 yr by pinkpanther