W123 engine swap advice - PeachParts Mercedes-Benz Forum

tampatech · #1 03-20-2006, 11:07 AM

Hi, I'm new here.

I recently purchased an '85 300D with a tired engine. I hoped that that it would get me by for a while. It didn't. Not being the sort of person to learn my lesson and cut my loses, I elected to double down. Now I have another '85 that was hit it the front end for parts.

The parts car supposedly has 200,000 miles on it. The radiator was busted and some parts already removed so I have not heard it run. I did a compression test with the following results.

#1 230 psi
#2 260
#3 310
#4 240
#5 270

I understand that these numbers are low and there is a large difference between the highest and lowest. This test was obviously done cold. The engine may not have been run in a couple years if that makes any difference.

The "good" car has zero rust (southern car), decent paint, fair but presentable interior and 240,000 miles on it. Everything works except the cruise control and power antenna, oh yeah... and that engine thingy.

I would like your opinions on the wisdom of doing and engine swap with this getting tired engine. Obviously there are no guarantees but how much life would you guess is left in it? If I thought it would last a couple years I would probably go that route rather than taking my chances on an $800 junk yard engine that may not be any better.

Any thoughts or suggestions would be appreciated.

bgkast · #2 03-20-2006, 03:22 PM

I'm no expert but those compression numbers seem low and the $800 price seems high. I would keep looking for a different engine.

t walgamuth · #3 03-20-2006, 05:42 PM

then before giving up on that motor i would try to get a radiator on it and start up and run it for a while with fresh oil. rig it to drive around if you can. then after getting it good and hot and such do the compression test. cant tell much from an engine that has been sitting so long.

tom w

Diesel Giant · #4 03-20-2006, 05:44 PM

Below 300psi is suspect, but they will run with care far below that. I would probably look at some others, but keep that one in reserve.

Stevo · #5 03-20-2006, 09:16 PM

If those numbers were obtained by cranking the engine cold, which i assume they were, You might not be too bad off. Those low 200#s might show closer to 300 with a proper compression test with a warm engine.

kirby_pug · #6 03-21-2006, 07:56 AM

I just bought a nice body 126 300SD with a junk motor & I had a parts car 123 with 320,000 miles on it & I thought the motor would be tired. After warming it up I found the compression to be 300 psi in every cylinder. Many people would be very gun shy about putting a engine with this many miles in but since Im doing it myself on slow days I did it & it runs GREAT!

If your doing the work yourself & you dont mind the work go for it. But I would not advise hiring out this work. Also dont get caught up in the trap of replaceing all these items just because "your in there anyways" If the motor mounts are still good leave them alone or take the better set from the 2 cars. Some like to buy $500-$1000 worth of new parts when doing this (ie oil cooler hoses, mounts, tranny lines, water pump,etc) Just replace what is bad if any. Although if the oil filter housing is leaking this is the time to do that.

tampatech · #7 03-21-2006, 10:05 AM

Thanks for all the good advice.

The parts car has been a parts car for a while and had a lot of parts scavenged already. It has no dash, steering wheel, exhaust manifold, turbo, etc so it would take a fair bit of work to get it running well enough to really warm it up. I am curious to know how the compression would check out warm but at this point I think I might as well proceed with the swap and find out. I intend to do the work myself. It will be the first time I have done this so I am sure it will take me a while but it should be a good learning experience.

I did run though a list of parts I thought I would need for the swap. Motor & transmission mounts, engine shock, gaskets, etc… I quickly had a $450 list of parts. I like your advice Kirby about getting in there and only replacing what really needs to be done. I will check out the oil filter housing and I do plan to replace the oil pan gasket “while I’m in there”. Do you think it would be a good idea to replace the starter now even though it seems to work okay? If the compression doesn’t improve when warm then it might benefit from a strong starter.

Thanks again for the suggestions. I would not have considered taking on this project if it weren’t for the great sources of information at this site.

tampatech · #8 03-21-2006, 03:36 PM

Hey, there is an engine on ebay right now item #8049471508. The price seems right although it would cost me a few hundred to have it shipped to Florida. Are those compression numbers for real? 480 psi? I thought spec for a new engine was 350 or so.

Panzermann · #9 03-21-2006, 04:11 PM

Quote:

Originally Posted by kirby_pug

Also dont get caught up in the trap of replaceing all these items just because "your in there anyways" If the motor mounts are still good leave them alone or take the better set from the 2 cars. Some like to buy $500-$1000 worth of new parts when doing this (ie oil cooler hoses, mounts, tranny lines, water pump,etc) Just replace what is bad if any. Although if the oil filter housing is leaking this is the time to do that.

I disagree with this. If you're just there "to make it go for the least," then not replacing things might be reasonable. But if your intention is anything beyond just making it go, then replacing anything suspect is easiest when the engine is out of the car. Working with the engine on a stand is pleasurable compared to trying to replace some parts of it while the engine is in the car. This is particularly true of a very high mileage situation. Those Mercedes engines may last forever, but rubber is rubber.

kirby_pug · #10 03-21-2006, 11:10 PM

panzermann: dont kid yourself, if these engines really lasted "forever" then this post wouldnt exist. He is after all talking about swapping out a bad engine for a used one. Just like I did Last month. Nothing lasts forever & if you replace everything your money wont last forever. Sure if you use credit cards then Charge away because its not real money till the bill arrives (if thats your attitude? sure isnt mine!) I do agree that if your mounts are bad Replace them but if your parts car has good ones use those. Why get the Dealer or Parts places rich when you have useable parts. Why even own a parts car if your going to buy everything new? Most everything that can be done with the engine out can be done with it in. I do agree with changeing out the oil filter housing gasket while the engines out. But if you have good mounts & oil cooler hoses that dont leak why bother?

The truth is I used to do the "replace everything while your in there" in the past & it dosnt pay. Replace everything that Needs to be replaced & thats it.

& dont think im some cheap ass owner because I change my oil every 2,000 miles & use Redline DFC, change tranny fluid every 15,000 & all other fluids.

Tampatech: Just remove the donor engine & take note on how it comes out & take your time removing your junk engine & take even more time installing the donor engine. Be patient & dont waste your coin on stuff that isnt broken.

t walgamuth · #11 03-22-2006, 07:29 AM

i agree with the last poster. i wouldnt change the pan gasket. they hardly ever leak. i might do the oil filter housing gasket. they do and it is easy with the engine out and almost impossible in. otherwise unless i saw an obvious leak i would not change things.

you will spend enough on things that are actually broken without doing a lot of prophelactic stuff.

if you spend an extra 1000 on stuff that really doesnt have to be replaced and you are in an accident next week, you wont get any more $ for your car cause it has a new pan gasket.

tom w

tampatech · #12 03-22-2006, 09:58 AM

I can see both sides to this debate. If I intended to own this car for the rest of my life then I would replace everything that I could while I was doing the engine swap. Then again if that were the case I would probably buy a $3500+ rebuilt engine rather than using one that has seen a lot of miles already. In my case I am looking to make it a safe, dependable daily driver that I will enjoy driving until something better comes along. This is my first Mercedes, my first diesel car for that matter. If I get hooked on them as most of you have, then I will be keeping my eyes open for one of those really nice, one-owner cars with maintenance records that come up for sale occasionally here in Florida. In the meantime I think I should try to keep my investment in this one to a minimum. The car will need a little front end work to be safe to drive and my budget is limited.

Thank you again for all your advice. I will post the results of a warm compression test when I get it running for the sake of comparison.