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MG MGF Technical - Why is it bad to warm up a car?

Occasionally this winter, it was so frosty that I had to start the car with the heater running for a few minutes to warm the windscreen. I use an MS sunmate so that there is no actual frost on it, but I didn't want to find frost appearing on the screen as I drove.

I have heard it said that it is bad for the car to idle it like this, but why? I went on to do journeys of ?30 miles so the battery'd be ok, and obviously idling the car is preferable to driving it with no forward visibility, but why is idling such a bad idea?
David Bainbridge

David,

In the bad old days (20 yrs ago or so) it was considered bad to warm up your car slowly because it meant that the working tolerances of the engine were not established quickly. Normal clearances for pistons, rings, bearings etc are calculated for a hot engine. All the time the car is warming up the tolerances are incorrect and wear is taking place. Once warmed up minimal wear takes place so it was better to warm up quickly by driving at reasonable speeds and revs and not by allowing the car to tickover for a long time with the engine cold.

If you catch my drift

Bruce
Bruce Caldwell

The biggest difference between then and now is the use today of full engine managment systems that allows precise control of the fuel mixture. In days gone by engines had to be started and run with the choke which is an imprecise device usually leading to a very rich mixture. Rich mixtures and low engine speeds leads to a condition called 'bore wash' where the excess fuel dilutes and washesaway the oil film providing lubrication between the rings and the bores. The result is very rapid wear in this area. Advice was to run the engine at 1500rpm with as little choke as possible if you needed to statically warm the engine before driving.

Even today it is still best to start and drive rather than let the engine idle till warm. Clearly when there is a risk of immediate screen freeze once you drive off after removing the overnight cover you need some warmth. The old advice of running at 1500rpm is still a good method or providing a quick low wear warm up, and with the K series this is only a few minutes.

Rog
Roger Parker

David, as others pointed wear is an issue regarding proper warming, but there's another: environment.

When an engine is under a load (pulling the car) it warms quickier than at idle. The faster it warms the better, as long as you don't take it too hard :-).
As a cold engine produces much more pollution (unburned hydrcarbo.) than a warmed one. That's why SAAB invented a system that stored (!!) the initial gases in a bag (!) and then injected them at small amounts in the induction after the engine was hot.

HTH, Valter~.
Valter

Valter,

>That's why SAAB invented a system that stored (!!) the initial gases in a bag (!) and then injected them at small amounts in the induction after the engine was hot.

Nah mate - you're getting mixted up with vacuum cleaners. ;-)
Paul Lathwell

>you're getting mixted up with vacuum cleaners. ;-)

No wonder, wasn't it a swedish company which founded the vacuum cleaner ?
Elektrolux ?

Carl ? ;)

Cheers
Dieter
PS. I'm sorry, couldn't resist. MoD is in brilliant mood currently.
Dieter K.

Mike, I used to have a engine heater wired into the cooling system, this would switch on with a timer and pre-heat the engine on my V8 GT, ideal on those frosty mornings,no sunmate then;-)
I understand kenlowe still make one, maybe someone knows if these are available??
Mike
Mike


Mini offer a pre-heat device in the brochure that, when you call it up and a standard mobile number, will pre heat the engine oil and even turn your electric seats !
Never seen it. Just read about it. Specifically talks about reduced engine wear.

P.
Paul Nothard

Although presumably, it is still best to let the engine idle for ~30 secs before revving to allow oil to circulate.

I'm guessing that whilst it takes maybe 10 minutes for the engine oil to reach an optimum working temperature (dependent upon outside temperature, nature of driving), that local hot-spots develop, around the pistons and oil is working OK sooner in these areas.

My start-up routine:-

- start engine (clutch depressed, no accelerator)
- wait on driveway for 30 seconds at idle
- pull-off
- keep engine speed below 3,000 rpm, until oil temperature gauge rises to 90°C


The above routine is partly influenced by a previous HGF and associated paranoia!
Philip

Philip

Exactly what I do, except wait for maybee 5 minuites then oil temp at 60º before going over 3k revs.

I used to have the pleasure/displeasure of living very close to Ferrari owners in our previous two houses - unbelievably, on the weekends both owners would trot into their garage, turn the starter, and instantly floor the throttle and preceed to rev the engine like mad. Now in my book that is the very worst thing you could do to any engine, let alone a Ferrari. Not the sort of people you tell this to though. I've had a few Ducatis in my time as well, and have always been advised to warm up the engine carefully (and respectfully) for a long trouble free life.

MJ
M J Roscoe-Hudson

This thread was discussed between 24/02/2003 and 25/02/2003

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