Myth or truth? Big engines question

[Pondrew]

I have heard many times over the years (and several times recently) people saying that big engines don't like lots of short journeys.
Is there any truth in this, or is it an 'old wives tale'?
I can't think of any logical reason why a 'big' engine (let's say 4.5 litre V8) should have any more problems with very short journeys than any other. Mind you, I am no mechanic and my knowledge of the ICE is very limited.

 

[Mr Tidy]

I don't think it does any engines any good regardless of their size as they never get properly warmed up. That's one of the reasons you get a build up of "mayo" on the back of the oil filler cap.

BMW M54 engines certainly don't like it. The only time I did that in my E46 next time I drove it I got a misfire and an Amber EML! Fortunately after I had done a few miles the misfire cleared and next time I used it the EML was off.

BMW N52 engines also aren't keen - it causes the common lifter ticking issue, although a decent drive clears that.

I'll never do it with my S54 engine because once I start driving it I can't help finding reasons to use the longest route possible. :lol:

 

[Smartbear]

I have heard many times over the years (and several times recently) people saying that big engines don't like lots of short journeys.
Is there any truth in this, or is it an 'old wives tale'?
I can't think of any logical reason why a 'big' engine (let's say 4.5 litre V8) should have any more problems with very short journeys than any other. Mind you, I am no mechanic and my knowledge of the ICE is very limited.

Maybe a contributing factor would be that larger engines generally take longer to warm up?
Rob

 

[Pondrew]

Maybe a contributing factor would be that larger engines generally take longer to warm up?

That seems to be logic, but why? Surely if it is bigger, it will have more oil, more friction, more coolant, all to the same ratios.
If you have a 2000cc 4 cylinder engine it will heat up at x
If you then bolted another 2000cc 4 cylinder engine to a common crank it would become a 4 litre 8 cylinder which surely would also heat up at x, not x times 2, as the friction is doubled (in fact probably more than doubled as it's got common parts therefore more to transfer the heat).

 

[Mr Tidy]

That's all getting way beyond my minimal technical knowledge, but someone may know!

What I have discovered since getting my MC which only shows oil teperature (rather than water) is that on free-flowing roads with 50mph or higher speed limits at this time of year it takes 8 or 10 miles before it is properly up to temperature. But if I get stuck in stop-start traffic in the summer it takes half the distance, so there are a lot of variable factors.

 

[Smartbear]

Maybe a contributing factor would be that larger engines generally take longer to warm up?

That seems to be logic, but why? Surely if it is bigger, it will have more oil, more friction, more coolant, all to the same ratios.
If you have a 2000cc 4 cylinder engine it will heat up at x
If you then bolted another 2000cc 4 cylinder engine to a common crank it would become a 4 litre 8 cylinder which surely would also heat up at x, not x times 2, as the friction is doubled (in fact probably more than doubled as it's got common parts therefore more to transfer the heat).

The greater capacity of oil would take longer to warm, the larger engine is also under less load so not working as hard which will tend to promote less heat being generated. Also larger engines tend to be taller geared so running less rpm for a given speed.
Just my opinion of course - Rob

 

[Pondrew]

That's all getting way beyond my minimal technical knowledge, but someone may know!

What I have discovered since getting my MC which only shows oil teperature (rather than water) is that on free-flowing roads with 50mph or higher speed limits at this time of year it takes 8 or 10 miles before it is properly up to temperature. But if I get stuck in stop-start traffic in the summer it takes half the distance, so there are a lot of variable factors.

Indeed. With modern fully synthetic oils, though, I would expect the viscosity to not change too much with temperature.
Your earlier comment regarding 'mayo' is due to emulsification of moisture mixing (or rather not) with the oil.
I know a little bit about a lot of things, but not a lot about anything (classic jack of all trades, master of none me)

I am just interested to find out stuff. Knowledge is power and every day should be a school day

 

[Mr Tidy]

Indeed. With modern fully synthetic oils, though, I would expect the viscosity to not change too much with temperature.
Your earlier comment regarding 'mayo' is due to emulsification of moisture mixing (or rather not) with the oil.
I know a little bit about a lot of things, but not a lot about anything (classic jack of all trades, master of none me)

With 5W30 or similar oils viscosity probably doesn't change too much with temperature, but my MC uses 10W60 and it's like treacle at ambient temperature!

I know what you mean about the "mayo", but if that happens you have to wonder how well the oil is protecting the engine.

And some thought-provoking input from Smartbear.

 

[Pondrew]

And some thought-provoking input from Smartbear.

Indeed. Roberto is one who doesn't shout too loud but is always the voice of reason and logic.

 

[Chris_D]

Every heat cycle is basically very gradually and progressively detrimental and destructive to your engine block and associated components.
This is why the term 'operating temperature' is commonly used within engineering as this usually refers to the optimum conditions for which any mechanical system can operate.

Friction, thermal transfer, contraction, expansion are all phenomena that take place in such systems and all contribute to the eventual end-of-life scenario for any given mechanical system, usually by things going out of operating 'tolerance' and subsequently failing.
When I was designing mechanical handling systems for the MOX plant at Sellafield (micron tolerances used in nuclear engineering) we would pre-determine the end-of-life scenario via maximum operating hours. Here, it was all about mitigating any risk of a failure of any system in operation which could potentially lead to alpha/gamma radiation leakage and/or loss of production. Hence, even though something like a robot arm could still be functioning perfectly and within its' design specification it would still be decommissioned as it would be nearing its' 'end of life'. I think it was after about 20,000 hours operation. By that time it would have completed so many duty cycles and absorbed enough radiation that the main threat to the arm would be failure of the flexible and susceptible internal components especially the power and control cabling being repeatedly exposed to fluctuating levels of radiation and heat from being used to extract and manipulate the plutonium cores from spent fuel rods. After that, it would be things like elbow bearings going out of spec. The maintenance engineers had a really cool way of determining the condition of bearings by measuring electronically how smooth they moved in operation.

Exactly the same principle applies to the engine in a car. Eventually things will go out of spec and fail and heat cycles will be a major contributory factor.
A well maintained engine, used correctly and sympathetically will last longer than one that's had infrequent oil changes and ragged or been subject to short journeys and not allowed to reach optimum operating temps.

My trusty old E36 coupe with the M52B25Tu engine which I used to commute around Europe for my business achieved 260k miles before it was t-boned and written off, but just before it was murdered I had recently done a compression test and it was still within factory specs. The rear cylinder was slightly lower as this is the cylinder that runs at the highest temps usually. Makes sense?

The point is, all those short journeys, track days, revving away from the lights just to get away first, pulling doughnuts, laying strips will contribute to the failure of your engine quicker than an engine that's been looked after. Simples.

I recently changed to 5w40 oil from 5w30 on my 147k miles M54B30 engined zed as a preventive maintenance measure. Always do intermediary oil changes at 7500k miles and never ever take it on short journeys. Shortest time allowed to be driven is at least 30 minutes and very rarely take it to the redline in any gear. Might make me sound boring but I'm more interested in longevity than having mindless 'fun'.
:wink:

 

[Pondrew]

The point is, all those short journeys, track days, revving away from the lights just to get away first, pulling doughnuts, laying strips will contribute to the failure of your engine quicker than an engine that's been looked after. Simples.

I get all that. BUT is there a difference in doing the same journeys in a larger engine'd car to a smaller one?
Going back to my original question; is it a myth or not?
My BIL made me re-visit this question. We were talking about cars recently. He had a 2001 Jag XKR (the 4 litre s/charged) about 15 years ago. It spent more time on a transporter than driving under it's own power, because it kept breaking down. I was ribbing him about how sh*te Jags are. He said "it's because big engines don't like short journeys and it did a lot of short journeys". My immediate reaction was "bollox, it's because Jags are sh*te". This, and the fact I am thinking of buying a big-engined car which won't be used much is the reason for the thread.

 

[Chris_D]

The point is, all those short journeys, track days, revving away from the lights just to get away first, pulling doughnuts, laying strips will contribute to the failure of your engine quicker than an engine that's been looked after. Simples.

I get all that. BUT is there a difference in doing the same journeys in a larger engine'd car to a smaller one?
Going back to my original question; is it a myth or not?
My BIL made me re-visit this question. We were talking about cars recently. He had a 2001 Jag XKR (the 4 litre s/charged) about 15 years ago. It spent more time on a transporter than driving under it's own power, because it kept breaking down. I was ribbing him about how sh*te Jags are. He said "it's because big engines don't like short journeys and it did a lot of short journeys". My immediate reaction was "bollox, it's because Jags are sh*te". This, and the fact I am thinking of buying a big-engined car which won't be used much is the reason for the thread.

Kinell fella, I think you're missing my point and the same point somebody else made that ALL engines, no matter what size will need to reach optimum operating conditions before any detrimental phenomena occurs.
The simplest/dumbest way to measure if a 'big' engine is going to suffer more on the same journey as a smaller engine is to drive the journey in both cars the journey and see if the temp gauge reaches the middle position - usually assumed as the optimum operating temp.
If they both do, no problem! If they don't, well there's your answer.
:roll:

 

[Smartbear]

The point is, all those short journeys, track days, revving away from the lights just to get away first, pulling doughnuts, laying strips will contribute to the failure of your engine quicker than an engine that's been looked after. Simples.

I get all that. BUT is there a difference in doing the same journeys in a larger engine'd car to a smaller one?
Going back to my original question; is it a myth or not?
My BIL made me re-visit this question. We were talking about cars recently. He had a 2001 Jag XKR (the 4 litre s/charged) about 15 years ago. It spent more time on a transporter than driving under it's own power, because it kept breaking down. I was ribbing him about how sh*te Jags are. He said "it's because big engines don't like short journeys and it did a lot of short journeys". My immediate reaction was "bollox, it's because Jags are sh*te". This, and the fact I am thinking of buying a big-engined car which won't be used much is the reason for the thread.

Kinell fella, I think you're missing my point and the same point somebody else made that ALL engines, no matter what size will need to reach optimum operating conditions before any detrimental phenomena occurs.
The simplest/dumbest way to measure if a 'big' engine is going to suffer more on the same journey as a smaller engine is to drive the journey in both cars the journey and see if the temp gauge reaches the middle position - usually assumed as the optimum operating temp.
If they both do, no problem! If they don't, well there's your answer.
:roll:

I’d say that the car which reaches its operating temp more quickly will be the longer lasting engine, as it’s running at the correct temperature for a longer period of time and burning off more condensation within the engine.
Rob

 

[Chris_D]

I get all that. BUT is there a difference in doing the same journeys in a larger engine'd car to a smaller one?
Going back to my original question; is it a myth or not?
My BIL made me re-visit this question. We were talking about cars recently. He had a 2001 Jag XKR (the 4 litre s/charged) about 15 years ago. It spent more time on a transporter than driving under it's own power, because it kept breaking down. I was ribbing him about how sh*te Jags are. He said "it's because big engines don't like short journeys and it did a lot of short journeys". My immediate reaction was "bollox, it's because Jags are sh*te". This, and the fact I am thinking of buying a big-engined car which won't be used much is the reason for the thread.

Kinell fella, I think you're missing my point and the same point somebody else made that ALL engines, no matter what size will need to reach optimum operating conditions before any detrimental phenomena occurs.
The simplest/dumbest way to measure if a 'big' engine is going to suffer more on the same journey as a smaller engine is to drive the journey in both cars the journey and see if the temp gauge reaches the middle position - usually assumed as the optimum operating temp.
If they both do, no problem! If they don't, well there's your answer.
:roll:

I’d say that the car which reaches its operating temp more quickly will be the longer lasting engine, as it’s running at the correct temperature for a longer period of time and burning off more condensation within the engine.
Rob

That's assuming that there was any existing condensate to be evaporated off or that the engine had not evaporated all the condensate that was produced while reaching its optimum operating temp (?)

 

[Roberltd2]

This has turned out to be an interesting thread opcorn:

 

[Smartbear]

I’d say that an engine which only just reached its normal temp by the end of the journey wouldn’t have had time to burn off all the condensation produced, it would have to operate at optimum temp for a longer period of time before that’s accomplished.
It’s all guesswork but I’d be uncomfortable using my car for regular journeys of less then 30mins even though it reaches normal temps after about 10/15mins or so :?
Don’t forget that the e85 displays water temp which reaches normal long before the oil does.
Rob

 

[Pondrew]

Kinell fella, I think you're missing my point and the same point somebody else made that ALL engines, no matter what size will need to reach optimum operating conditions before any detrimental phenomena occurs.
The simplest/dumbest way to measure if a 'big' engine is going to suffer more on the same journey as a smaller engine is to drive the journey in both cars the journey and see if the temp gauge reaches the middle position - usually assumed as the optimum operating temp.
If they both do, no problem! If they don't, well there's your answer.

So your answer is to conduct a very expensive and long-winded experiment?
Thanks, I'll think about it.
PS I get the feeling you may have some anger issues.

 

[mgrlane]

I think you have 1st got to define the definition of "warm".

Many people will look at the water temp and think the car is "warm" as soon as it "gets in the middle".

The reality is (in my (often) stupid opinion) is that this water temp means very little.

I think you have also got to ask the temperature of "what" contributes to "warm". Is it water temp? Engine oil temp, gear box oil temp?

My AMG I don't believe shows water temp (not easily anyway) but I drive it in AMG setting and it displays at all time engine and gearbox oil temp (other settings are sat nav, direction, speed etc).

When the engine oil hits 80 degrees the colour of the temp setting changes from white to blue and all systems are go (basically like an M where you get the extra couple of 1000's on the rev cycle). An interesting point is the newer 63's (w205) tolerance for being warm is 10 degrees cooler than the w204.

In terms of getting to optimum running temp my car will get there within 3-6 miles (the engine is a 6.2- I might have mentioned it). So it looks like it heats up considerably quicker that your iron block M's on here?

 

[BeeEmm]

Views please on this real life scenario. I have read on this forum, that a lot of people start the engine, then leave the car to 'warm up' before moving away. I always believed that this was wrong and that you should drive of immediately with reasonably low revs in each gear. I have also read the manufacturers instructions which advised the same. I have a BMW plug-in hybrid car with a 3.0 straight six petrol engine as well as the electric motor. The electric motor easily takes me to the M25 where I can build up speed to 70 mph (I know, unusual for the M25). The cold 3.0 litre engine will then 'kick in' at that or slightly lower speed and cruise happily. The change from electric to ICE is barely noticeable.

 

[mgrlane]

The electric motor easily takes me to the M25 where I can build up speed to 70 mph (I know, unusual for the M25). The cold 3.0 litre engine will then 'kick in' at that or slightly lower speed and cruise happily. The change from electric to ICE is barely noticeable.

I have thought about these engines before. I am interested to see how the petrol engine lasts. My understanding is that when you need extra power it will kick in the petrol engine so there are various times that you will be driving on electric and need that extra shove so a petrol engine is started and then put under load with effectively no warmth in the engine.

Is that the case? Is it an electric car that gets assisted by a combustion engine?