Long run improves running - why?

[David53]

Just completed another nice long country drive, about 400 miles round trip. Today I did about 130 miles in one go, and this included some heavy hill climbing (down to second gear) and some long stints of motorway cruising. I noticed that towards the second half of this long stint the car was running noticeably better, nice and smooth and idled nicer at the lights once I hit the big smoke again. I'm aware that a good hard run like this kind of cleans things out but what is it actually doing?

[Dean]

I think the oil being hot and thin has something to do with it. I agree though, when I am doing the annual run to the national my mog sounds and runs the best it ever does.

[chrisryder]

Cars generally seem to handle better after a long run as the tyres get hot, the air expands, increasing the tyre pressures. But no idea why you've found it to improve the engine running!

Coincidentally I did 400 miles (over two days) the other weekend going around the country. And the 200 mile non-stop journey on the way home certainly seemed to feel better and better. Got home beaming! Bluey certainly felt very happy, engine-wise too.

Could be uniform distribution of heat. I imagine in short runs, although when up to normal running temperature, some bits are still warmer than others. But after a good long run, all that heat soaks around uniformly... I could just be talking out of my DONT SWEAR OR YOU WILL BE BANNED though.

[Alec]

Hello David,

cars that do a lot of short runs tend to coke up a bit inside which a good run clears out. Cars that are driven hard do seem to run better.

Alec

[moggiethouable]

In addition the exhaust gets good and hot, as they rot from the inside this is beneficial as you are drying it out thoroughly.
The battery gets a thorough charge too, and the engine a bit of a decoke.
They are meant to run I suppose, not stop and start intermittently.
I dont think its your imagination.

[MarkyB]

I should think the gearbox oil will warm up too from conduction from the engine.
Even the diff oil from being churned about.
Some of it is probably psychological, I'm always listening for new noises that might mean trouble at the start of a long journey but relax once it's been running for a while.

[autolycus]

Well, we've had all the technical explanations, most of which I find unconvincing, so let's add "because after driving a Moggy for 200 miles you're as deaf as a post, so you no longer hear the noises that previously held you back from keeping your hoof down regardless".

Kevin

[David53]

No, it's not lack of noises. The engine was definitely running a little more smoothly and was more responsive than it had been previously. I presume it's due to the de-coking of the engine, but my question is why does this happen after a long drive and why did owners have to manually decoke the head in years gone by but we no longer have to?

[Dean]

Better petrol David that cleans as it combusts perhaps.

[mowogg]

I would imagine the improved running of the engine is due to the abundance of free radicals, which are formed from the long journey. This will ensure the engine runs more freely

[bmcecosse]

I like that idea - I've always been a bit of a free radical.......

[chrisryder]

I wouldn't mind a free Radical...

[MarkyB]

http://en.wikipedia.org/wiki/Free-radic ... y_of_aging

[JOWETTJAVELIN]

You DO still have to decoke as carbon still accumulates. Even on an unleaded head which was fitted brand new about 5000 miles ago yeilded a considerable amount of cack. Long runs are good for the engine esp. high speed cruising as it is having an easy time yet everything is getting a good blast through. As others suggest the proper warming up of components will no doubt have something to do with it.

[MikeNash]

David,
I think a contributor to your good running after a long run is just that the oil reaches a higher temp and so getting thinner with an associated drop in friction thus allowing the engine to give a little extra noticeable bit of available power. (Note, most of us use SAE 20-50 as opposed to BMC's recommended SAE30.)
I've a temp guage in the sump and only on long journeys at a brisk pace will the oil get above 80C, a temp generally considered the low end for oil health. You needn't worry about over cooking it; I find I can only reach oil temps of 95-95C by driving at 60-65 mph (true) in air temps around 25C with a full load aboard or towing a trailer, and then only after a few hours of motorway driving. Regards, MikeN.

[bmcecosse]

At that temperature - you need an oil cooler Mike !

[bmcecosse]

On the long run - everything loosens up. Wheel bearings run free, brakes stop rubbing that wee bit - and yes the engine/gearbox/final drive all loosen up and run more freely. Even the tyres warm up and roll more easily - and the pressure rises slightly too, further decreasing the rolling resistance.

[MikeNash]

Roy,
You only get 90-95C when driving hard on hot days - and I'd forgotten that was with my old engine (pre the one I bought from you!) that used a pint of oil every 200 miles, so that after a long hard drive (up the A1(M) to Newcastle I'd only got half a sump full left! No wonder it got a bit warm.
No, our real problem is getting and keeping the oil hot enough, MikeN.

[bmcecosse]

I had endless problems on my rally Minor - until I fitted a cooler....... Maybe if you use fancy modern 'synthetic' oil you can get away with 90/95 degrees - I prefer to see at least 60 psi on the gauge, which I could never hold until the cooler went on.

[MikeNash]

With due respect M'lud, oil pressure readings mean little without an associated oil temperature. For instance on my engine I only get 60 psi when cold i.e. when the relief valve is relieving. A quick bit of shopping today with a round trip of 14 miles at 40-60 mph gives an oil temp of 150F (65C) and pressure at 40 mph of 50 psi. I'm happy with that.
Re synthetics, I'm trying to sort out my fuel flowmeter to get some figures using Wilkinson's 20 -50 oil and will try some 5-30 synthetic. Good names are getting cheaper - and BMC recommended SAE 30 anyway. Regards,MikeN.