Do I really need to rebuild this engine?

November 10, 2008 4:46 PM

I now have a car with a seized engine. If I can get the engine unseized, what are the potential consequences of not rebuilding it?

The car in question is a '93 Hyundai Excel. As long as I have owned it, it has burned a quart of oil every 600-1000 miles (yet it miraculously still passes emissions). The engine seized because it burned too much oil -- someone drove it for a mile with the oil light on.

Getting the engine unseized might be possible, but all the advice I have seen on this ends with "Then, rebuild your engine." Rebuilding it myself, having it rebuilt, or buying a rebuilt engine are all expensive, and I would end up with a crappy car that still needs a lot of other work done. I'd rather save that kind of money for a more reliable car (or bike).

So, the cheap option is to try and get the engine unstuck, but forget about rebuilding it. Is this likely to end in disaster? Burning more oil? Burning less oil? Any advice on this (or on the general situation, like how to get the engine unseized), would be appreciated.

posted by rossmik to travel & transportation (12 answers total)

If it's been going through that much oil for so long, it's already had some pretty serious problems and probably has been in need of a rebuild.
I'd even say that you've been incredibly lucky it hadn't seized before now.

I would think that getting the engine unsiezed would require a rebuild in the first place. There's also the problem that when the engine seized up, it might have done itself some serious internal damage.

It's an old car. A new engine wouldn't have the problems your current one already did, and would probably be cheaper. A new car would be even cheaper still.
posted by dunkadunc at 4:59 PM on November 10, 2008

"unseizing" it won't mean it runs; it just means it rotates. An engine seizes when one of either the main or rod bearings go dry, rotate in their journal, and jam up against the crank. Sometimes rotating the crank backwards will unwedge it, but the engine is almost certainly toast. You may get lucky and only need to replace the bearings, but at that point you're wayyyy inside the engine, and it's not worth it to just replace parts and button it back up, vs a rebuild or a replacement.
posted by notsnot at 5:03 PM on November 10, 2008 [1 favorite]

With most cars, once the engine has seized, replacing the car is almost always more cost-effective than replacing the engine. Your seized engine is probably not rebuildable--if the engine block didn't crack, the cylinder walls and pistons have probably melted and there really isn't a way to "unseize" an engine.

One option would be to buy a rebuilt engine and have your mechanic install it, but with parts and labor you're looking at roughly $2500 to $3000, so you need to decide if you want to invest that kind of money in a 15-year-old car or put it towards something newer.

My advice would be to sell the car to a junkyard and buy a newer car. Much of your decision depends on the degree of emotional attachment you have to the car and what you want to do with it, but unless your 1993 Hyundai Excel had only a few thousand miles on it and ran like it did the day you drove it off the showroom floor, it's almost certainly not worth a whole new engine.
posted by mattdidthat at 5:11 PM on November 10, 2008

I doubt you can unseize the engine and then not rebuild it. What happens when an engine seizes is, the lack of oil film between the piston and the cylinder causes the two to grind against each other directly, removing metal from both. Eventually heat builds up, the cylinder and piston are all ground to hell, and they stick together nice and tight from friction.

In addition, it should be noted that oil lubricates more than just the pistons in the cylinders. It also lubricates bearings in the piston rods. If those bearings lose oil and stick (called a "spun" bearing), they have to be replaced also.

So it all depends on what exactly happened to your engine. Most shops would actually just replace a seized engine on a car this old, if they can get a replacement. It's a lot cheaper in terms of labor. Unseizing will require, at a minimum, a lot of penetrating oil and patience just to get the pistons moving again. Even then, a compression test is likely to tell you that there's major scoring of some or all of the pistons/cylinder walls. Those walls will then have to be bored out, and the pistons replaced with larger ones. If you've spun any bearings, those will need to be replaced... the list goes on. I don't see this repair being worth it. And in my opinion, you can't unseize the engine and not rebuild it. It won't run again without repair.

If you want to sell the car for any reasonable sum of money, look into an engine replacement. It may be cheaper than you expect, but you'll need to do the math on the resale value with a running engine. I think you could get a new motor for $500-$800. Replacement could be done for as little as $600 in labor if you can find a shop that specializes in that. If the sale price of the running car would be $3k, that might be worth doing.
posted by autojack at 5:15 PM on November 10, 2008

You should sell the car for scrap. A junk yard might pick it up for free. You don't say how many miles on the engine, but as others posted, there is no way you can rehab it w/out opening it up the engine to almost the same point as a rebuild.

If you are really attached to this car the better choice is to buy an already rebuilt engine and install that.

Consider that its "a crappy car" already and an emissions disaster to boot. Save your money and get a nice bike. You'll also save gas, insurance, parking tickets, etc.
posted by TDIpod at 5:18 PM on November 10, 2008

When an engine seizes, it's because certain rotating parts expanded beyond their allocated range for expansion, and the now-bigger part could no longer rotate. Consequently, it stopped rotating, often very suddenly.

Case in point: Once upon a time, I had a Honda Accord that used a qt. of oil every 1k miles. And, of course, being a lazy and broke student, I let it run below it's safety threshold, which given the other abuse this engine withstood, must have meant that there was no oil at all in the crankcase. In any event, I seized that motor up real good. When it seized, it didn't all stop at once. Instead, some parts seized immediately, and others tried to rotate a little more before seizing. The metal parts that were connected by gears, such as the oil pump drive shaft (which was connected by a gear to the cam shaft), sheered off some teeth on both the drive shaft and the cam shaft, ruining both. All in all, it proved much cheaper to simply replace the motor with another used motor than to attempt to rebuild the pile of slag the old motor had become.

Moral of this story: a seized motor does not typically just start back up again. It's very likely dead, with extensive internal injuries, and only a thorough rebuild will really fix the parts that are broken and the parts that got damaged but maybe didn't break.

You can possible find a running replacement motor fairly cheap -- think "cars damaged by Katrina" -- but your current motor is toast and needs to be rebuilt to be reused. Sorry.
posted by mosk at 5:19 PM on November 10, 2008

It depends on what sorts of parts are damaged. Cracked things -- pistons, rods, crank shaft, flywheels, cams, valves, springs, and on and on -- will prevent the engine from running properly, or at all. Ruined seals will prevent the engine from running for very long. Then, there are bearings. Chances are extremely good one or more of these are ruined.

By definition, you've got rings seized to the cylinder walls. You're going to have to take the heads off, soak the cylinder's in penetrative oil, and use mechanical force to get them moving again. The tools required for this, the time, and the expertise make this an expensive and time consuming job. In the end, the pistons probably won't seal, and basically the engine won't run without a rebuild. You'll have spent all that time disassembling the engine for nothing sans a rebuild.

Your cheapest bet is to locate a used engine somewhere (salvage yard) on the cheap (the exact same engine, mind you) and swap it yourself. You could probably rent all of the tools from Autozone and do it yourself in a weekend with help from the internet. It's actually not as difficult as it might present itself to be. That's what I'd do.
posted by luckypozzo at 5:19 PM on November 10, 2008

The only reason I would ever ask a mechanic to try and rebuild a seized engine (and it would have to be done by a mechanic, because no shade-tree is going to be able to un-seize the parts by themselves) would be because the engine or car was so rare and valuable that it needed to be saved to keep the components of the car "matching."

I cannot think of a single reason otherwise.
posted by Civil_Disobedient at 5:44 PM on November 10, 2008

So many things can go wrong with an engine after it has already seized - even if it can be unseized - that I can't even begin to recommend rebuilding the engine you have now and hoping it'll have been worth it. Money down a hole, based on my personal experience ('88 Nissan Sentra, had no idea the oil light wasn't functioning...d'oh).

Your choices are going to be:
• Get a new engine
• Get a different rebuilt engine
• Use what you'd spend on either as purchase or down payment for a less broken vehicle

Whatever you end up doing, good luck.
posted by batmonkey at 5:59 PM on November 10, 2008

As everyone else has said, you can't just "unseize" an engine and use it again, it needs to be rebuilt or replaced to a tune of $2000-3000. You can buy a perfectly good car for $1000 or less, so unless you have a strong emotional attachment to this car and money to burn, I'd write it off. If the rest of the car is in good shape you can probably sell it for a couple hundred to a shade-tree mechanic (who can fix it for much less and re-sell it at a profit or give it to his kid).
posted by bizwank at 5:59 PM on November 10, 2008

it has burned a quart of oil every 600-1000 miles (yet it miraculously still passes emissions).

This is just 'relatively high oil usage'. There is no reason for it to affect emissions, nor is there any reason to claim/assume that it was at all related to the initial failure. The oil light generally comes on below an astonishingly low oil pressure related to the amount required to run the engine without lasting damage. I have been amazed that manufacturers are still able to leave such a low theshhold on such a major failure.

The engine seized because it ran out of oil. Possibly almost completely. It ran out of oil because it burns it while it runs (as do al l engines, to differing degrees). It is almost certainly either impossible or not in the slightest bit cost effective to rebuild it unless, as previously noted, the car/engine is incredibly rare or of very high value.

It's a 93 Hyundai, so none of those apply. Either buy a second hand engine (from a crashed one, perhaps) and have it installed, or walk away from the car and learn that ignoring oil levels is a stupidly expensive error. It's the single most important element of car maintenance.
posted by Brockles at 6:55 PM on November 10, 2008

Thank you all for your advice. Best answers were marked where people suggested what types of damage there might be (I didn't know about spun bearings), but all of your advice helped. If this were a good car, I would be encouraged to try replacing the engine myself, but as it is, I'm going to take TDIpod's advice and save my money.
posted by rossmik at 9:36 PM on November 10, 2008