whats worse for a cold engine?

[madmelon]

Originally Posted by kempster1

All mechanical and electrical engineers should be made to do a trade prior to studying engineering.

..yeh the 4 years of my life and 20G's it's cost ME (yeh, ME, not my parents or family or friends etc) doesn't cut the mustard ay.

You haven't tried to be at all helpful, rather flaming someone for explaining what happens AND why in terms anyone can understand. If I've made a stuff up somewhere I'll gladly be corrected but nobody has said anything so far.

A forum is about learning and being helpful where you can. Be a contributor or naff off.

[ebxr8240]

You need some load on an engine...
Just drive normal ...Not like a di[khead...
Leaving an engine to idle is not the best either...
Buy the time I put my seat belts on etc is about as much time required for
oil to get around internal parts etc...I'd say no more than 1/4 throttle...
An auto is much easier in this dept as it always has load on engine...

[kempster1]

Originally Posted by madmelon

Load: Bad because applying higher cylinder pressures to a cold engine will result in more blow-by and increases the possibility of gases creeping past the head gasket, causing it to fail. Older english cars are notorious for blowing head gaskets with even a slight thrash when they're cold. As the engine warms up, the pistons expand as does the block and head, which reduces the clearance around the piston and increases the clamping force on the head (dependant on materials- an all iron engine may actually lose clamping force due to the lower coefficient of expansion of irons compared to high tensile steels.)

RPM: Bad because the oil is not warm and so is still thick. Giving an engine high revs when it's cold will greatly increase the stress on the oil pump gears and drive, possibly causing premature failure. If the the oil can flow into the pump sufficiently at that temperature, the high oil pressure created may blow out seals etc (again thinking about clamping forces) but if it can't suck the oil it wants, it may cavitate, causing pump damage and possibly causing starvation at the bearings. Another thing is how long it takes to run back to the sump- if all the oil is up the top, then say goodbye to bottom end bearings.

The thicker oil generally puts more stress on all engine components as it takes more torque or force to move them. Also, oil consumption is not helped either as the thick oil is more likely to stick to the bores as the scraper ring comes past. This plus greater cold clearances is why you get blue (oil) smoke when you give it to a cold engine.

Some better comments about your original post
I not sure how many people on this site have an old english car to warm up every morning.
The parts that your talking about warm up very quickly, idling cyclinder temp would be over 200 Deg C, so items like pistons and rings warm up almost instantly when the engine is started. All the other items you spoke about in the load section are taken care of by modern gaskets.

Oil pumps are designed to pump oil, they have pressure regulator valve and pressure relief valves to prevent them from being overloaded and getting damaged.
Multi grade oils take care of all the problems you discribed relating to the oil being cold.

For me the answer to the original question, as long as you have good oil pressure and do not flog the car for the first 100 metres.
That all you need to do to warm a car up.

[ltd]

The important thing for an engine when cold is not to rush. Start the car, let it idle for the time you put your wallet, phone, coffee etc in place and then drive it gingerly. Short shifting is a good idea until the engine temperature guage starts to move off the stop and is on its way up. For those with automatics, just use the throttle lightly until you get some temperature in the engine. In aviation, one of the preflight checks is to have the oil temp and pressure in the normal range. Failure to allow the oil temperature and pressure to come up to normal will cause premature wear and can result in premature engine failure on takeoff.

In turbines, the engine oil temp and pressure again have to be up to temp/press normal ranges before taking off or again, failure can occur. If you have an engine failure on this type of aircraft and you failed to check or commenced takeoff without them being normal and you have an incident, then CASA will define this as substantially contributory to the incident and you will be held responsible.

It is unthinkable to try and operate an engine at any less a minimum standard. If you are the type who likes to thrash an engine from the time you start it then you should do an oil change, and then run a magnet around the bottom of the container you collected the used oil in. If you find that the magnet has got lots of little fine bits on it then you have your answer to the cold start question.

[vztrt]

Originally Posted by madmelon

..yeh the 4 years of my life and 20G's it's cost ME (yeh, ME, not my parents or family or friends etc) doesn't cut the mustard ay.

You haven't tried to be at all helpful, rather flaming someone for explaining what happens AND why in terms anyone can understand. If I've made a stuff up somewhere I'll gladly be corrected but nobody has said anything so far.

A forum is about learning and being helpful where you can. Be a contributor or naff off.

Mate dont worry about people like that, your better off ignoring these people. They're exactly like the electrical contractors I have to deal with. You have to hold their hands because some of the stupid things they do is absolutly amazing, like how can you put a one way drop lead on the wrong way...oh wait use a hammer....

[Hybrid34]

Thats why the REmote Start was invented, not just a t0ss3r function

[DBourne]

Originally Posted by Hybrid34

Thats why the REmote Start was invented, not just a t0ss3r function

not sure how it'd work when you're meant to leave your car in gear..

[Wally]

In old cars you had to let the engine fast idle for a 30 seconds just to stop it from stalling. This gave the fuel copious time to pour into the pots and give the sidewalls a good rinsing to get rid those pesky lubricants.

These days engines don't rely on the manifold heating up enough to vapourise the fuel; even cold start injectors are no more.

At cold idle the oil pump is not moving much oil around and about the only way to get it circulating sufficiently is to get the revs up.

[ltd]

Originally Posted by Wally

In old cars you had to let the engine fast idle for a 30 seconds just to stop it from stalling. This gave the fuel copious time to pour into the pots and give the sidewalls a good rinsing to get rid those pesky lubricants.

These days engines don't rely on the manifold heating up enough to vapourise the fuel; even cold start injectors are no more.

At cold idle the oil pump is not moving much oil around and about the only way to get it circulating sufficiently is to get the revs up.

Oil pump is circulating at idle from startup, it is also in fact often circulating more pressure than normal due to the oil being under-temperature and therefore thicker. What I think you meant is that in the first second or two of startup whilst the pressure builds is where most of the engine wear occurs. This is not however arrested by revs. In fact, this is exacerbated by revs. For example, a mate used to have an EL XR8. On cold mornings, he'd start it up and rev the crap out of it under the guise of "warming it up". In the two years he owned it he managed to score the bores in 5 of the 8 cylinders, as well as blow a total 7 oil filters apart where the body joins the base. This was all because he thought revving it was good.

When they pulled the engine apart his warranty claim was denied on the basis of abuse, and ironically he used to drive it pretty calmly. I at the time had a DL 5 litre, and never had any of the issues he did. I just started it up, waited about a minute before driving it off slowly. This also helped the transmission and I only did a slightly leaking extension housing seal at 140,000klm. Again this was to guard against the higher pressure caused by the colder fluid.
As for ford saying not to let it idle, this is partially to prevent rust and corrosion in your exhaust from water vapour getting trapped in your exhaust and not being blasted out from exhaust gas heat and pressure. Also, this advice is from the same people who say never to service your transmission for the life of the vehicle. They are correct though in not letting your car idle if you aren't going to drive it, as this can cause corrosion in the heads too and lead to premature spark plug failure, as well as unneccessary coke build up.

Oh, and before you think of taking me on or try to belittle my knowledge of it, I'd suggest facts and not supposition. I know engines and although through my ATPL I studied turbines and turbo fans such as the RB211 and the JT9-D, oil lubrication necessities are much the same for bearings and friction surfaces whether they be titanium, alloy or iron.

[Wally]

No I meant that you have to get the revs up for good circulation; I am not suggesting anyone "rev the crap" out of it.

I'd be interested to know what your oil pump volumetric rate is at idle, even with cold oil, and what it is at cruise revs. Static pressure with a thick oil does not translate to the same flow of a thin oil at the same pressure. Pumps are sensitive to specfic gravity and will almost always pump less with a higher head as the specific gravity increases. Raising the revs to fast idle with either a choke knob or autochoke was fairly common for quite a few decades when carbies were the go and I'm not sure it invalidated warranty?

Fear not I'm not about to "belittle" your input and experience, but as your are experienced with turbochargers, you'd know that when checking the flow through the CHRA into a milk bottle, the reduced flow when at idle and cold is noticeable.

I'll have to take your word for

ford saying not to let it idle, this is partially to prevent rust and corrosion in your exhaust from water vapour getting trapped in your exhaust and not being blasted out from exhaust gas heat and pressure

. I heard something like this before, but never seen it substantiated in a Ford (or any other maker's) TSB so if you have a copy I'd be interested.

My experience is limited to hands on modification and rebuilding of engines over a 30+ year period and I can't comment on scored cylinder walls and burst oil filters from over revving, because I've never seen either in my builds... lucky I guess.

[madmelon]

Originally Posted by ltd

For example, a mate used to have an EL XR8. On cold mornings, he'd start it up and rev the crap out of it under the guise of "warming it up". In the two years he owned it he managed to score the bores in 5 of the 8 cylinders, as well as blow a total 7 oil filters apart where the body joins the base. This was all because he thought revving it was good.

That's what I was getting at as well. There might be oil pressure relief valves...but try blowing cool honey through a straw and see how it goes.

[Wally]

Originally Posted by madmelon

That's what I was getting at as well. There might be oil pressure relief valves...but try blowing cool honey through a straw and see how it goes.

Oil pumps have a relief valve to regulate the oil pressure to about 40 - 60 psig. The only way you'd blow an oil filter is if the relief valve was faulty or too slow opening. Giving the engine a prolonged ragging at startup might just beat the relief valve action, but I'm sure that's not the intent of this thread.

[Van D]

I turn my car idle, heaps of choke so it doesn't cut out for about 30 seconds then straight to work. It still stalls on cold mornings sometimes coming to a stop etc if it's all not right, but the engine's never let me down.

Neither have any of mine, or families car from been driven from cold.

[ltd]

Originally Posted by Wally

No I meant that you have to get the revs up for good circulation; I am not suggesting anyone "rev the crap" out of it.

I'd be interested to know what your oil pump volumetric rate is at idle, even with cold oil, and what it is at cruise revs. Static pressure with a thick oil does not translate to the same flow of a thin oil at the same pressure. Pumps are sensitive to specfic gravity and will almost always pump less with a higher head as the specific gravity increases. Raising the revs to fast idle with either a choke knob or autochoke was fairly common for quite a few decades when carbies were the go and I'm not sure it invalidated warranty?

Fear not I'm not about to "belittle" your input and experience, but as your are experienced with turbochargers, you'd know that when checking the flow through the CHRA into a milk bottle, the reduced flow when at idle and cold is noticeable.

I'll have to take your word for . I heard something like this before, but never seen it substantiated in a Ford (or any other maker's) TSB so if you have a copy I'd be interested.

My experience is limited to hands on modification and rebuilding of engines over a 30+ year period and I can't comment on scored cylinder walls and burst oil filters from over revving, because I've never seen either in my builds... lucky I guess.

Fair enough. Without going into specifics oil pumps are generally rated at a higher pressure than needed to prevent wear when cold, which is why oil pressure tends to be higher at cold startup; to take into account the thicker viscosity without starving the engine from lubrication.

I have no experience with turbo's, what I have studied extensively and have passed my examinations on is turbine engines, engines as small as the pratt and whitney PT6 750 shaft hp turboprop up to the GE90-115B turbofan with 135,000 shaft hp (think boeing 777).

These engines have very sophisticated lubrication systems and although turbine temperature often reaches 1200 degrees celsius before actually starting, their lubrication even at the first primary spool up is crucial.
As in these engines and in ICE the oil pumps pump a static pressure, which is easily exceeded on revs with a thicker oil. When the static pressure is exceeded that is where you can have problems such as blowing seals etc. As the oil heats up it loses some of its viscosity and ergo is at a lower pressure for the same revolutions.

To overcome problems with this as well as fuel introduction into the combustion chamber, manufacturers devised an auto start feature, much the same as fuel injection for your car. In the older pratt and whitney turbofans which had manual fuel introduction, it wasn't infrequent for passengers on planes to see a 50 foot long flame explode out of the rear of these engines due to overzealous fuel supply and/or a dirty hot section.

Anyway I digress, but you can actually do a lot more damage with higher revs and cold/thicker oil than with hot oil. This is why I drive my car gingerly when cold and always let it idle for a few moments.
To combat this problem however, manufacturers are now using much lighter viscosity oils such as the 5w-20 used in the 3v V8.

[ltd]

Originally Posted by Wally

Oil pumps have a relief valve to regulate the oil pressure to about 40 - 60 psig. The only way you'd blow an oil filter is if the relief valve was faulty or too slow opening. Giving the engine a prolonged ragging at startup might just beat the relief valve action, but I'm sure that's not the intent of this thread.

I'd say that he would also have had heaps of contaminents in his oil due to the amount of blowby he would have generated, not to mention the fact that he changed his oil as per the handbook which would have allowed for more degredation. His oil pump nor the pressure regulator where found faulty, but again thats not to say that ford service departments are absolutely perfect in diagnosing pressures of valves in situ.

[XR6BF24V]

i agree only an engineer knows the value of a sky hook or was that a left handed screw driver or an ....

[nugget378]

Whoever thinks there is less blowby without any load on the engine obviously hasnt ever built one,otherwise you would know that the rings are designed to seal better with some cylinder pressure,the combustion gasses need to get between the rings and expand them,try bedding in the rings on a rebuilt or new motor with no load and see how long they last,talk about a puffing billy.

It beggars belief that you can equate a prop engine to one in a car,while I dont know much about aircraft it doesnt take a genious to work out that the prop places a load on the engine,so in reality its not like a car idleing in park.
I also dont get the idea of a daily driver needing a few moments to circulate oil,its not like it has been sitting for 6 months,there is enough of an oil film on bearings from yesterday's driving to cover those first few fractions of a second till the pump circulates some oil.

And one more thing,low oil pressure does not necessarily mean the bearings are running dry,an engine can show only 10psi oil pressure and still have more than enough oil,bearing clearances have more to do with this than return spring pressure..
I never warm up a car,just start and go,and bearings always come up looking like new.
The only time I prime the pump is when the car has been sitting for a long while,and then I crank it with the ignition diconnected till it builds some pressure,then start and go...

[ltd]

^^^^^^^^^^

Ok, the amount of blowby I was referring to is from a cold engine, cold and ergo unexpanded metal irregardless of rings. There is substantial load at idle on the engine regardless. This thread isn't about bedding rings once installed, it's about day to day operation of an ICE.

If you read my post I merely suggested driving it gently until some heat is generated in the motor so that the oil is more fluid (ability to move), has coated more surfaces within the engine and that the friction surfaces have started to expand to within their normal operational tolerances.
I have rebuilt motors as well so I do have a little knowledge in this area.

The lubricating properties of oil for example are substantially diminished as a coefficient of temperature. If you pour some GTX2 out of a bottle that is at room temperature it will take longer to empty than the same bottle of oil heated to 100 degrees celsius. Hydrodynamic friction does not occur instantly regardless of oil pump pressure and therefore damage to crankshafts and bearings is directly proportional to temperature, viscosity, condition and revolutions.

Furthermore, one of the functions of oil is to help seal the microscopic imperfections of friction surfaces such as cylinder walls and/or piston rings, excessive revs before substantial oil flow can encourage blowby to contaminate the oil prematurely. If you want to substantiate this then flush your oil, put in new oil and try driving your car gently until it starts to gain temperature in the engine after starting. 3000k's later do an oil change and note the colour. Now flush and repeat the process and drive it harder upon startup. 3000k's later do your oil change and note the colour. I'll bet you'll find the darker oil is the harder driven oil.

As for turboprop motors, there is no load from the prop pulling on the engine as most have a pneumatic coupling (think torque converter but with air instead of fluid).
Turbofans are the same as the actual turbines themselves are separate so therefore receive no directional loading. My comparison with these engines and ICE's is to demonstrate the lubrication requirements of an engine turning at 30,000rpm with bearings costing up to half a million dollars each, and then the rubbish they stick in cars worth 25 dollars each. Friction is friction, and to avoid unnecessary wear it requires lubrication and not overspeeding in certain conditions.

One last thing, as for bearings running dry, I don't believe I mentioned that, or where you referring to someone else in this thread?

[Wokkas]

Originally Posted by kempster1

All mechanical and electrical engineers should be made to do a trade prior to studying engineering.

Spot on. What's stated in books, and what actually happens are two completely different things...

[T3rminator]

In my T-Series manual, on page 112 it suggests various ways to conserve fuel economy. One of the bullet point includes "Warming the engine is not necessary". The T3 runs on 0w-40 (factory recommended).

Despite this I always let the car idle for ~30 sec on cold starts.

[Circle_Wurkin]

Id agree with that last point, it is not neccessary, the internal temperatures of the combustion chamber are pretty damn hot which heats up the oil pretty quickly and at the end of the day thats what you need good free flowing oil to lubricate those moving parts coz remember THERES ALWAYS TIME FOR LUBRICATION and anyways the temp gauge on your dash is how hot/warm the coolant is not how hot the engine is and its really only a guide.