'Warming up' a car

decoy · Post by **decoy** » Wed May 19, 2004 1:46 pm

I've recently been wondering about warming up a car. Is the main purpose of warming up the car to get the oil warm or to get the oil curculating up and around? if its to get the oil curculating, if you have parked your car after it was running a bit hot (half way on the gauge), you do somthing quick then get back in the car, lets say the oil has settled by then. the temp gauge is still operating temp but do you need to 'warm' the car up a bit again to the the oil going around? or does the oil take so long to settle that the engine would be 'cold' again by the time it actually has settled?
Also lets say you start your car on a cold morning, the auto choke has it revving at around 1700rpm, your on a flat road and don't have time to warm it up. what the difference between idleing at 1700 and putting it in 1st and taking off, never exceeding 1700rpm, changing to 2nd, doing the same etc. the only thing i can think is the drivetrain is connected and spinning as well, hence no difference for the engine? or does having it in gear put load on the engine because instead of free spinning, its having to spin the rest of the drivetrain? then again its only going 1700rpm so will it make a difference?

Black JA · Post by **Black JA** » Wed May 19, 2004 1:50 pm

ummmm... :? ???

ProZac · Post by **ProZac** » Wed May 19, 2004 1:59 pm

Warming up your car in the morning means making sure your car is at NOT (Normal Operating Temperture) before you drive off. This allows for the oil to be at the correct viscosity and circulating around the engine properly, so when you place load on the engine, the oil is there to protect it. It also lets hot water heat the intake manifold and help with fuel atomisation. Plus you dont have to freeze your nips off driving down the road waiting to turn the heater on. I think warming a car up mainly harks back to the old days of carburettors and manual-chokes, when a car would actually be damn hard to drive when it was cold.

If you drive for a while, get out to do something quickly, and get back in, the oil will never settle. Infact it'll never settle aslong as the engine is running, as its constantly being pumped around the engine, aslong as the engine is rotating. Our engines also have fancy little oil squirters that lubricate one side of the bore (the loaded side) to help with the boost aswell. Study the lubrication system of our engines, its actually pretty interesting tracing the pathways through the head and rocker towers.

If you are driving down the road in 4th at 1700rpm, pop in the clutch pedal, what does your engine rev up to? The load of the drivetrain, friction from spinning things and the road means the engine has a significant force opposing its motion, meaning it's only revving at 1700rpm, without this friction i bet you'd be somewhere around the 3000rpm mark. Its all about load.

I used to warm my car up for 5 mins every morning till the temp gauge sat where it was supposed to. Some people said it really made no difference, and even if it didnt, it made me feel better :).

decoy · Post by **decoy** » Wed May 19, 2004 2:10 pm

ah cool

i also meant that when u left the car for a bit, the engine was off. hence why the oil would settle, but still be hot.

also thinking about the drivetrain and the oil in there, they are not warming up when the car is idleing, so that would be a good reason to driving slowly at low rpms while warming up the car, when the engine has curculated the oil around a bit of course.?.

ProZac · Post by **ProZac** » Wed May 19, 2004 2:17 pm

Ahhhh, if you switch the engine off, then back just a short while later, nah no need to sit there i dont think, those oil pumps work pretty crazy fast, so it gets up to the head pretty quickly. No probs there.

And you'd be right about letting your diff and gearbox warm up i'd say, so no thrashing it when your first out on the road :).

You pose interesting questions, where are our gurus!?

Black JA · Post by **Black JA** » Wed May 19, 2004 2:28 pm

:roll:

Project2501 · Post by **Project2501** » Wed May 19, 2004 3:37 pm

I think the aim of warming up the car in the morning (after it has been sitting for hours) is to get a film of oil over the components. The time taken for the oil to reach correct (such a thing?) viscosity depends on the weight of the oil. You certainly dont want to drive it (applying load to the components) without a layer of oil there protecting it as ProZac said. But once it has been idling for a few minutes, I think itd be safe to say that the oil would have had time to fill the galleries and circulate around the moving components, which is the whole point, isnt it? I know some people that drive off after 2 mins or so of waiting, while some others put a broomstick on the gas pedal and go back inside to brush their teeth/eat brekky/etc, which i think is really overkill.

If youve only switched the car off for a few minutes, id doubt the oil would have had time to drip back to the sump completely, a thin film would still be on the components. Regardless of that, there should be oil already in the pump and galleries for you to take off again relatively quickly.

BTW have you seen the Castrol Magnatec(sp) ad?

cheers

tom.

decoy · Post by **decoy** » Wed May 19, 2004 3:57 pm

hehe, yeh i was gonna say my example was exempt of magnatec! hehe. waiting for someone to bring it up

Will · Post by **Will** » Wed May 19, 2004 8:14 pm

Another factor is that metals expand at different rates, so when an engine is built, the tolerances are setup to be correct when at operating temperature. For example, your valve clearances are different when cold vs. when at operating temp. Your piston to bore clearance will change with temp etc.

My general rule of thumb is, give your engine about 30 seconds warmup if you're starting from complete cold before moving. When moving, take it easy until at least the temp gauge starts to move, don't go real hard until at operating temp (about halfway on the gauge).

scum · Post by **scum** » Wed May 19, 2004 8:39 pm

i work in hydraulics, and trust me, oil isnt going anywhere in a hurry. even when hot it can take days to 'drip' of stuff (including our roof) the only prob with shutting hydraulic equipment down is most of it is not designed with turning off in mind. about the only thing allot of it has is various 'soft start' clutches and stuff so the engine can start even when the hydraulics is under load. and there is the prob, when under load engine and hydraulic pistons 'push' against one side of the cylinder wall and causes a metal on metal contact, if you try to run it oil has a hard time getting back into that spot and the equipment can run for minuets sometimes without oil in one little area, release the load and the oil is straight in there. sometime in the 60's they fixed most of these probs by cutting little groves around the piston to let the oil get under or over the affected area and cause equal pressure across the diameter of the piston to straighten it out and let oil get all around it. the moral of this huge post is the oil grove / ring in your pistons is there for a reason and dont put too much stock in what your great grandad tells you! like someone said be4, 30 sec warm-up when hot should be fine. as for warm up when cold, how many years do you have? forget it, im not typing all that. the basics: oil wont go into small places when its cold. you need to heat it up first. in newer engines like ours they worked all the thermal expansion crap out, for example, steel cylinder lining can heat up and expand at the same rate and same size as the aluminium piston. even though there different materials. they just work this out by metal density and thickness and any kind off alloy mixed with it and lots of other stuff that i have no idea about. its the oil you need to heat up more than the metal of the engine. so there you have it, a post that makes bugger all sense. I’m going home.

Cookiemonster · Post by **Cookiemonster** » Wed May 19, 2004 8:41 pm

I agree with Will.

When we used to do karting if you didn't allow the engine to warm up it would seize. Different metals expand at different rates so you have to allow the all parts of the engine to come upto temparture before you put too much stress on it.

scum · Post by **scum** » Wed May 19, 2004 8:45 pm

o yegh, i forgot go-karts did that. well, there different coz..... errrrr i cant remember. i might be lack of cooling system. naaaa that wasnt it, preformance orientated? uhhhh, might have been. anyway, them and those horrible briggs and stratton engines (and british things) but a JAP engine wont.

edit: sorry, going off track, i'm talking about pistons only really, not valves n stuff.

Cookiemonster · Post by **Cookiemonster** » Wed May 19, 2004 8:47 pm

Hmmmm.. our kart engines had Yamaha written on them. I wonder if they were Japanese.

scum · Post by **scum** » Wed May 19, 2004 8:52 pm

i remember when i was told all this crap that there are plenty of exeptions to the rule, but not in the jap car 4-6-8 range. ever bin to one of those engine blowing up comps where you cant have a sump or radiator? ever seen a jap engine blow first? HA! wont happen, watch the V8's go first HAHAHAHA!!! well, exept for that lousy stinking V8 a couple of years ago..... :x

Cookiemonster · Post by **Cookiemonster** » Wed May 19, 2004 8:57 pm

I think YOU are the exception to the rule. No offense.

Austarion

'Warming up' a car

'Warming up' a car

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