As engines age...

H

HappyWax

New member
Ok so we all know that as an engine gets older the power is "lost" I'm curious to know a couple things:



1. Is there is a general rule of thumb when it comes to how much power is lost over time? -ie Car X has 150hp New from the factory- at 100,000 miles it will produce apx ____ hp. and at 180,000 miles?



2. Is power loss even a relevant, measurable amount?



3. -Is the power lost at the crankshaft or at the wheel (ie the loss of efficiency through out all the moving parts)
 
1. No.

2. Yes.

3. Power loss is cumulative, but generally, it comes from the fact that over time, engines lose compression due mostly to wear on the rings. While its' not an overly complicated thing to change out on a common US V block engine, it is exacting work.



There are some relatively simple things that can be done to restore that power once the engine is out of the car, or the head is removed.



Think of the engine as an air pump. The more efficient the pump, the more power it will make. Seal it up super tight, and that bad boy is going to get the most it can out of it's displacement.
 
depends a lot on maintenance...most of the loss is due to loss of compression...



as the drivetrain and bearings 'loosen up', they actually consume less power...



here's a Cummings engine...

12k mile oil changes, 300k miles, almost no power loss

in fact at power peak of 2100 it GAINED power!



with 25k miles oil changes, and only 250k miles, it loses a lot of power ~20%



Editor-Fig3.gif
 
scoach hit the nail right on the head.. wear in cylinder walls, and piston rings (what makes the seal between each piston and its cylinder's walls, causes reduced compression... valves seals can also wear and distort somewhat, also contributing to lost compression and over all performance... where your rockers touch the top of your valves, the clearance there also grows, resulting in a louder running engine (tapping) and the valves not being opened as far... valve adjustments are a simple way to gain power on an older motor, which involves putting the clearance just mentioned (between rockers and the top of valves) back to factory spec, to allow the valves to open fully, and the motor to run more quietly.
 
As long as the engine is well maintained and doesn't lose compression it will gain power as it loosens up.
 
Wear and tear seem to be the concern here, but like Jason M suggested, what about a seasoned motor? A lot of motors in cars make less power off the factory line, than they will 1 or even 5 years later.
 
Generally no real loss in power until something starts to fail, such as rings, valve seats, cam lobes, whatever. Rings can wear a certain amount before they negatively affect power. I'd say as a general rule, most modern cars with good maintenance that are driven reasonably will go 200-300k miles before power really starts being affected. As mentioned in a previous post, usually engines make a little less power at first due to extra friction and poorer sealing before all the parts get worn in.
 
And even as rings wear, so do the cylinder walls. This makes the engine looser due to the reduction in friction but the engine still "seals" fine since the walls wear in the same pattern. Do a read up on "hard break in" of engines. Most race/high perf. engines are broken in this way.
 
Since piston rings are exandable, they do compensate for the wear both in themselves and the cylinder walls, so its only as they get older that compression is lost. Compression can also be lost through wear in the valve seats and valves.



One thing that hasn't been touched on but relevant to the question since most people here are petrol heads is that the fuel will also make a difference. Most diesel engines wear more slowly than gas, reaching higher mileages before suffering compression loss. Though I have to say that as I sit here and write that, any explanation for that completely escapes me!
 
butchdave said:
Though I have to say that as I sit here and write that, any explanation for that completely escapes me!
Click to expand...



Probably related to the fact that their static compression is so much higher and they run on autoignition.
 
Lower RPM, stronger parts, diesel acts as a lubricant, tapered rings, etc.



Basically diesel engines are made to have a longer service life. If would be easy to build a gas engine that lasted for a million miles. Of course it would weigh a ton, rev to 2500RPM, and make 50ft/lbs or torque. You get the idea. It's a balancing act.



Change your oil, avoid detonation, maintain your fuel system and modern gas engines should have no issues going for 150-200k without losing compression.
 
butchdave said:
One thing that hasn't been touched on but relevant to the question since most people here are petrol heads is that the fuel will also make a difference. Most diesel engines wear more slowly than gas, reaching higher mileages before suffering compression loss. Though I have to say that as I sit here and write that, any explanation for that completely escapes me!
Click to expand...



I would assume that this is due to the lower temperatures that the motor runs at. Gasoline motors run pretty hot. Deisel on the other hand, ignites and burns at a lower temperature. Slower motor speeds might contribute, as there would be less friction involved with a motor, who's redline is 4k rpm.
 
Jason M said:
Lower RPM, stronger parts, diesel acts as a lubricant, tapered rings, etc.



Basically diesel engines are made to have a longer service life. If would be easy to build a gas engine that lasted for a million miles. Of course it would weigh a ton, rev to 2500RPM, and make 50ft/lbs or torque. You get the idea. It's a balancing act.



Change your oil, avoid detonation, maintain your fuel system and modern gas engines should have no issues going for 150-200k without losing compression.
Click to expand...



What he said...
 
Of all that, I'd go with the lower RPM as the main contributor, after all, less movement - less wear. Yes temperature and lubrication from the diesel etc will assist, but I suspect the largest factor is simply the lower RPM.



But if that were the case then lower revving, more torquey gas engines would also last longer, and I've not noticed it being a particular factor.



Of the engines that last longer, I'm of a feeling that its more to do with drivers than design. Diesels don't attract the high revving, heavy footed drivers, and the longer lasting gas engines seem in my mind to also to be those that attract shall we say the more mature driver. Perhaps too though, the older driver tends to me a bit more affluent and able to afford regular servicing.



Interesting concept, though not exactly what the OP was asking.
 
Temp has almost nothing to do with it. An engine can be designed to run at any temperature. And diesels exhaust gas temp is actually higher than most gas engines anyway. Lower RPM is also not a major factor. The main deal is that they are designed to be stronger from the start.
 
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