Warm up procedure - I just don't get it?

[fimbo]

In the latest edition of Evo (105) ('Ask the Experts'), Jeff Daniels ("the UK's most experienced and prolific writer about car technology and the motor industry" - EVO) is of the opinion that it is better for an engine's longevity to blip the throttle immediately from cold to get the oil circulating to places like the camshaft (which with the apparent oil starvation issues highlighted on these forums seems particularly relevant) and to get the engine at least warm before driving off. From reading these forums, and the advice dispensed by TVR, I think generally (I say generally) accepted wisdom is to keep revs below 2.5/3k until oil temp above 60 degrees and to drive off immediately after turning the key - in other words, don't let it idle and don't run it up and down the rev range sat on your drive.

The latest wisdom from EVO's 'expert' seems to go against the grain of advice on these forums. So what's what on this issue. Mechanics/Engineers and those with knowhow, please speak up.

[softtop]

I cannot see the difference.

Keep the revs above idle to get the oil flowing as you said, and don't rag the arse off it until it is warm

Edited by softtop on Friday 4th May 12:39

[W7 KAA]

I was also under the impression it was better for all other compenents of the vehicle to gently warm up whilst on the move.

Better for the engine, but also the added befenefit of breaks, suspension, clutch and gearbox etc all warming up on a gradual basis.

No engineer though!!

[W7 KAA]

or brakes even!!

[ridds]

Whilst on the move you are laoding the rings due to creating pressure within the cylinders.

Sitting on the drive and reving it does not apply the same loads and can eventually lead to bore glazing.

Providing you keep the revs down and the throttle off the floor then driving is the best way to warm up an engine.

[dvs_dave]

Start the engine normally without applying any throttle (maybe a little dab if its very cold) then once the engine has fired, gently increase the revs and hold at about 1500-1800 rpm for 30-60 seconds (gets the oil pressure up and circulating properly). Then drive off as you normally would keeping the revs below 2500 until the oil temp is over 50degC. It's now safe to use up to 50-60% throttle. Wait until the oil is above 60degC before going over 60% throttle.

[bertbert]

dvs_dave said:

Then drive off as you normally would keeping the revs below 2500 until the oil temp is over 50degC. It's now safe to use up to 50-60% throttle. Wait until the oil is above 60degC before going over 60% throttle.

Just out of interest, where does that info come from? Who works out that that is actually mechanically correct? why 50 and 60, why not 45 and 55? why 60%, not 50%? Is it based on tests? What?

The reason for asking is that I have a suspicion that it stems from when engines have had inherant reliability problems, so the manufacturers end up in problem-management mode until they actually solve the real underlying problem. But the warm-up routine is firmly ensconsed by that point. Same happened with Caterham R500 engines, caterham came up with all kinds of mods and advice until they fixed the actual underlying problem (big end shells). But the regimes created still stay.

Bert

[dvs_dave]

Just my routine. Being a mechanical engineer with a fair amount of experience working with medium size piston engined gensets (up to 2MW) which are essentailly just oversized car/truck engines. They use the same oil. They should'nt be loaded up until the oil reaches 50degC and you should avoid full load until the oil reaches 60degC. For emergency backup power systems, they're equipped with block heaters to keep the engine and oil at a minimum 50-60degC. This means that they can safely withstand full load operation within 10-15 seconds of startup. Not following this routine will quickly end up with you landing a $150k rebuild!

Hydrodynamic bearings (such as big end and main bearings) are particularly sensitive to oil viscosity and only funtion correctly under high loads when the oil in them is at the optimum viscosity. Typically for a multigrade motor oil this is between 50 and 100 degC.

Edited by dvs_dave on Sunday 6th May 23:05

[ZooOOM]

I'd just like to add that the gearbox and diff have their own separate oil supplies from the engine. Some people advocate idling the engine on the driveway to warm it up, but of course, this will not help the gear box or diff.

Incidentally, I agree with the previous comments which suggest that you should drive off immediately, one, the oil pump produces more flow and therefore more lubrication, and two, hydrodynamic and squeeze film lubrication of bearings and cams are more effective, not to mention reduction of chatter due to correct loading of the components.

By the way, I'm an engineer with a tribological background (study of friction, lubrication and wear).

[fimbo]

more out of necessity than good habit I have always started up my cars and then driven them off immediately. It's always seemed like a total waste of time, let alone fuel to leave the thing idling on the driveway. I don't quite understand why loading the engine when cold (albeit gently) should accelerate engine wear - but then I'm no mechanic/engineer. Is the Sp6 different from any other engine in that respect?

[yzf1070]

fimbo said:

more out of necessity than good habit I have always started up my cars and then driven them off immediately. It's always seemed like a total waste of time, let alone fuel to leave the thing idling on the driveway. I don't quite understand why loading the engine when cold (albeit gently) should accelerate engine wear - but then I'm no mechanic/engineer. Is the Sp6 different from any other engine in that respect?

In a nut shell..... the oil feed to and around the cylinder head is poor, the inlet cam receives fresh oil first and the residual has to make its way around to the exhaust cam. As oil is also a cooling medium it would have made sense to do it the other way around or even better still do it as per the AJP6 engine design and feed oil to the cams from both sides of the block and head. Some engines were assembled with dubious quality components which exacerbated the problem(the sintered metal cams that wore out in my engine are testament to this). Warm/hot oil flows better than cold viscous oil, thrashing an engine from cold risks starving the "load bearing" components of lubrication, plus its never wise to do this as the rotating components expand whilst taking up built in tolerances. Its far better to let everything warm up and settle to regular running temps before loading up an engine. Personally I prefer to drive straight off rather than leave it standing to warm up, as you mention, its a waste of time and fuel.