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I am considering getting a new engine for one of my cars and I was wondering if I'll have to change the odometer too. Since the car already has 220,000 miles on it, it would become a huge number if I used the same odometer on a new engine.

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    Replacing the odometer is going to make bookkeeping very difficult. Oil change: 200,000 | 208,000 | 216,000 | 4,000 ?? Followed by Alternator: 6,000 ?? If you're installing a new engine at 220,000 then that's a simple bookkeeping entry. A used engine just needs to make a side note of the used engine mileage. – MonkeyZeus Oct 28 at 13:49
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    In the UK, MOT vehicle testing automatically builds up a database of annual odometer readings as a fraud protection measure and three years of history is printed on the MOT certificate, so unless you reset the new one to the old mileage you are potentially going to create problems for yourself, quite apart from selling the vehicle etc. – alephzero Oct 28 at 14:02
  • Now I wonder if resetting an hour meter (when equipped) is common when an engine is replaced. – JPhi1618 Oct 29 at 15:08
  • @JPhi1618 I would change/reset any hour meters – PeteCon Oct 29 at 15:18
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    Getting a new engine isn't usually something you 'consider' doing - either it needs to be replaced or it doesn't. Unless the alternative you are considering is the scrapyard? – J... Oct 29 at 15:39
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I wouldn't touch the odometer. The rule I always subscribe to is that the odometer measures how far the chassis has rolled. Otherwise a person could go mad trying to figure out which repairs/replacements should reset the clock. (Obviously not tires or wheels, but wheel bearings? Axles/driveshaft? Transmission/differential? etc...)

It also makes sense when you think about the disconnect between the number of hours an engine has run vs. the distance it's traveled. Work trucks, limousines and police cars all can spend a significant amount of their life just idling, and that's not reflected in an odometer reading because the chassis never went anywhere in that time.

  • Don't forget that many modern car security systems link the key in your pocket, the dashboard clocks and the ECU. Replace one and you'll need to get the immobiliser re-coded. – Steve Matthews Oct 29 at 10:49
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    The odometer of Theseus. – Studoku Oct 29 at 12:45
  • It's like I've always wondered about those people who replace the wheels with lower diameter wheels to reduce their ground clearance - making the wheels have to turn that much more to achieve the same horizontal travel, presumably this messes up both the odometer and speedometer (in addition to inviting damage to the chassis since it can't go over even a minor pothole or road debris without scraping the bottom...) – Darrel Hoffman Oct 30 at 18:14
  • @DarrelHoffman the difference is proportional to the diameters ratio and is not that significant. And the speedometer is intentionally biased to higher readings (psychological trick to slow cars down). – Crowley Oct 30 at 21:01
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    @Crowley Actually (according to Wikipedia, EU has regulations that a car speedometer "The indicated speed must never be less than the actual speed", and I understand then that manufacturers, to account for mfg tolerances, will purposely read higher to prevent breaking those regulations. So no psychological trick, just erring on side of not breaking laws. – mharr Oct 31 at 21:35
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I've never replaced an odometer when replacing an engine. What I will do, however, is make a note in the cars documentation that the engine was replaced at xxx,000 miles with a new/refurbished engine with xx,000 miles. I also keep all the receipts of any ancillary parts replaced at the same time (tensioners, water pumps, etc), so that a new buyer can see that the work was done correctly.

This way, you're staying legal, and you're making the replacement engine a positive aspect when you come to sell the car.

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You're probably better off not replacing the odometer. You will need to keep accurate track of how far the car has been driven in total, so if you were to later sell your car without disclosing that the actual mileage is the new odometer reading + 220k miles, you could be found guilty of fraud. You certainly don't have to replace the odometer, and it will only increase the amount of bookkeeping you need to do, so it'll be simplest if you don't.

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    +1 for the fraud mention. In many jurisdictions, it's actually illegal to change the odometer unless it's broken or the entire dashboard is being replaced. ISTR that some dealers (possibly in the EU?) actually have to contact the factory and order a replacement odometer with the same mileage as the one being replaced. – TMN Oct 30 at 13:47
  • @TMN: You should be able to match or exceed existing odometer with any replacement without factory assistance. If it's already past your existing reading, no problem (except it reduces the value of your car). If it's less, hook it up to a power supply and an oscillator on the wire that normally goes to the transmission, and let it spin until it reaches a matching value. – R.. Oct 30 at 14:45
  • This doesn't actually answer the question, which is: "When is it not fraud to change the odometer?" – jpaugh Oct 31 at 16:22
  • @jpaugh Not sure how you got that from either the question title or body. The question is "Am I required to replace the odometer when replacing the engine?" - the OP never mentions fraud at all. – Nuclear Wang Oct 31 at 16:50
  • @NuclearWang Your answer assumes the OP's decision will be fraudulent, but the OP assumes it will not be. I'm merely restating the question in terms of the facts that you have mentioned. More to my point, without talking about what situations would be fraudulent, this doesn't answer the question: replacing every part except the odo would be just as fraudulent as replacing only the odo: But where is the line between those two extremes? – jpaugh Oct 31 at 18:31

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