Why shouldn't you warm an old engine up on tick over?

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nickthe fish
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Why shouldn't you warm an old engine up on tick over?

Post by nickthe fish »

I'm having a debate with some one about this, I can't explain to him why you shouldn't warm an old engine up on tick over all I know is that you shouldn't do it.....

Can anyone give me an explanation why????

Thanks you please,

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AdrianC
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Re: Why shouldn't you warm an old engine up on tick over?

Post by AdrianC »

nickthe fish wrote:I'm having a debate with some one about this, I can't explain to him why you shouldn't warm an old engine up on tick over all I know is that you shouldn't do it...

No different for an old engine as a new one. Idling gets warmth into the engine very slowly, compared to driving.
For a petrol/LPG engine, whilst idling, the engine is running very rich, and that can wash the lubrication film off the cylinder walls increasing wear.
For a diesel, it pisses the neighbours off.
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Re: Why shouldn't you warm an old engine up on tick over?

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Red Westie
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Re: Why shouldn't you warm an old engine up on tick over?

Post by Red Westie »

ooooer! I think there are more reasons why you SHOULD warm your engine up (idle it for a couple of minutes) than there are for driving it straight away.
The pistons haven't expanded to fit the cylinder bore so piston slap (movement in the bore) wears both piston and bore more from cold.
'Under load' conditions, the THRUST side of the bore wears more dramatically....so with limited splash lubrication (from thicker oil) and a loose 'slapping piston' putting the engine under load from cold is not the best idea.
Much fewer piston strokes at idle and little thrust effect without the throttle being open.
Around 28 strokes per second for each of the pistons at idle
BUT as many as 175 strokes per second (redline) THE IMPORTANT THING HERE IS 'UNDER LOAD'

Cold oil doesn't circulate as well and the act of 'splash' lubrication (under the pistons on the bores) is reduced because of the more viscus oil (again not good for reving from cold)

It is an advertised fact that 50% of the engines wear occurs in the first few minutes or so the Castrol advert would tell us.

I agree that your points are valid but what I'm suggesting is idling 'without load' for a couple of minutes is 'the lesser' of two evils and allows oil to thin, pistons to expand and mixture to reach lambda 1, before the stress is applied.

Martin
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Re: Why shouldn't you warm an old engine up on tick over?

Post by AdrianC »

Red Westie wrote:The pistons haven't expanded to fit the cylinder bore so piston slap (movement in the bore) wears both piston and bore more from cold.

If you're getting piston slap, then the long term health of the engine's irrelevant - it's already knackered.

Cold oil doesn't circulate as well and the act of 'splash' lubrication (under the pistons on the bores) is reduced because of the more viscus oil (again not good for reving from cold)

Cold oil tends to see far higher oil pressures - and, again, you've not got the bore wash to contend with as far as cylinder wall lubrication goes.

I agree that your points are valid but what I'm suggesting is idling 'without load' for a couple of minutes is 'the lesser' of two evils and allows oil to thin, pistons to expand and mixture to reach lambda 1, before the stress is applied.

I'm not suggesting thraping it off the instant the starter motor's stopped spinning - of course it needs to be driven gently until there's some warmth in it, but equally you don't need to wait until the temp gauge is up to normal before driving off - or even just starting to show. Start it up as you get in, sort your act out, belt on, then drive off.
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Re: Why shouldn't you warm an old engine up on tick over?

Post by Red Westie »

Your opinion.....My opinion....
Let me re-phrase 'piston slap' I was using it as an exageration to hi-light the basic warm up process and the fact that pistons are generally slightly oval when cold and expand round to properly fit (well clearance fit) the cylinder bore.
I also notice you ignored what I wrote about the thrust side of the piston and bore and seemed to want to concentrate of 'bore wash' so please indulge me: The choke comes off quicker when being driven because the engine is under load and creating more heat, yes? but the engine is reving higher and under load during that shorter time period. Yes? so if we could count the number of strokes during that shorter period would it be more or less that idling the engine for say a couple of minutes? admittedly anyones guess.....the point is it maybe a shorter time period but I'm summising there are at least as many engine cycles, if not more but they are under load with the piston acting hard upon the thrust side of the bore and lubrication not at it's prime.
The choke in affect delivering the same amount of rich mixture (in quantity) but over a shorter time but critically UNDER LOAD.....now tell me which scenario causes the most wear?
Good debate tho.


Martin
Last edited by Red Westie on 25 Mar 2011, 10:07, edited 1 time in total.
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Re: Why shouldn't you warm an old engine up on tick over?

Post by Allanw »

Two minutes of idling won't get the pistons (or anything else) anywhere near operating temp. It will still be cold after 2 minutes of running. Some parts will have started to expand, some won't. The exhaust valves will be the warmest part of the entire engine.

Driving heats more of the parts, more evenly.

After idling for two minutes, basically all other parts (transmission, shocks, bearings etc) are all cold anyway, so they need to get to operating temp. The only way to acheive this is to drive it.

Having said all this - when was the last time you had an engine wear out from bore wash???

I had a SUbaru that spent the first 200,000kms of it's life being started, reversed down the drive then pulling out into traffic - accelerating hard to the 70Km/h limit It was still going strong at 320,000kms. Never used any oil.

Once oil pressure is up, it's basically everywhere it needs to be. At startup, the thick oil is squirting out of big end bearings basically as much as it is at operating temp. If it isn't close, you have the wrong oil.
Allan :-)

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Re: Why shouldn't you warm an old engine up on tick over?

Post by BOXY »

A long time ago I was an engine technician in the RAF. I used to work on Bulldogs which had a 200-hp Lycoming IO-360, flat-four piston engine (air-cooled obviously). There was a written procedure for starting the engine and part of it was letting the oil temp reach a certain figure before increasing the revs from idle. If warming up an engine works for aeroplanes, I'll stick with it for my van.

Has anyone put a Lycoming engine in a VW?
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Re: Why shouldn't you warm an old engine up on tick over?

Post by kevtherev »

oil heats up a lot quicker by friction when it's forced through galleries at 50 psi... not at 18 psi (idle)

it's oil that has to heat up ...not the engine.

The 2.1 has a device where by the oil takes extra heat from the coolant.. so the quicker you put in the quicker it will get thinner

So just driving the van is better for the engine..it's a fact
2.1 DJ on pierburg + LPG

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