How much notice once a 3.5L diesel starts bending rods??? - PeachParts Mercedes-Benz Forum

bhatt · #1 03-27-2006, 02:44 PM

Hello all,

Considering buying a 1992 300SD (W140 w/rod bender engine)

First of all, let me say: yes, I know of the (potential) engine problems.........

I have found one that is in nice shape and am considering buying it. It has 100,000 miles and it is undetermined as yet whether it has the original or a rebuilt engine. By the time I do the minor repairs needed/pay all the taxes/etc, I would have $1000 (canadian) into the car.

The guy is 3hrs away from civilization so I'd have a heck of a time taking it to my mechanic. Not that he'd know if the rods were bent anyway! (is there any test for this at all??)

Here's my thought:
-Look over the car on my own and make SURE the following 4 things work: A/C is cold (prove the evaporator isn't leaking), stereo works (Bose amp OK), wiring harness isn't cracked (check multiple places), and that the vacuum trunk/doors work properly.

-If all that stuff checks out and the car runs well, would I be safe to buy it, knowing that I'd sell if the rods ever started bending? I would NOT be interested in spending the money to rebuild that engine.. would sell it and either buy another diesel, or just get a gas W140.

So here are the 2 big questions:
1. How much notice do I have once the car starts using oil before it's "obvious" that there is a problem? If I were to trade it into a dealer for example, how much time would I have before they test drove it and screamed "engine problems!". I'm guessing it is a slow process over 10,000 miles or so???
2. What % of these engines went either "forever" or "a really long time" without EVER having a bent rod? I am pretty sure I read here that it was NOT a 100% failure rate. I remember reading something about either 50% of the cars having experienced bent rods OR that 50% will ever experience bent rods (big difference between the two!). If I'm at 100,000 miles already, I would take the 50/50 chance if that's the case. I assume at 100k mi if it hasn't gone BANG the chances of that ever happening are <10% or <20% or so?

Thanks!
Neal

PS. In case you're wondering, I want a W140 but CAN'T bring myself to sell my W126 300SDL. Keeping the current car isn't an option and I really HATE to buy a gas W140 (even though I know it might be cheaper overall to buy a gas one & maintain it since the prices are lower on the used market, I really prefer the diesel ones!)

Hatterasguy · #2 03-27-2006, 10:31 PM

Do a search on the diesel forum their is a lot of thought on this subject. But $1k for a 350SD is so cheap just buy it anyway you can resell it and make money!

What happens is you start noticing the oil consumption going up and up, until it burns so much you can't drive it. It seems to happen pretty slowly, plenty of time to trade in for another car.

DslBnz · #3 03-27-2006, 10:51 PM

There are TWO I am tracking right now. Each with completely different symptoms. Both consume oil at least 200 miles to the quart consistently.

One has so much blowby it blew the front crankshaft seal. It has low, low oil pressure (almost 0 at idle, not even .5 bar). It does not start very willingly. It is constantly engulfed by a blue cloud of smoke. The idle throbs, the engine shakes enough to nearly toss itself out of its braces, and is essentially undriveable. DON'T YOU DARE OPEN THE OIL FILLER CAP WHILE THIS THING IS RUNNING. IT WILL SEND THE CAP INTO ORBIT.
It uses about 150 to the quart last time I measured, if I recall correctly.
That one's mine.

The other, I mentioned earlier in the archives, has much more subdued symptoms. Maybe a cracking injector (or rod clanking against the cylinder) at higher rpm. Idle is very smooth, no blowby at all, power is plentiful, a darkish blue haze at idle, and copious amounts of oil at higher revs. At highway speeds, it burns considerably more oil (130 miles to the qt). You'd never know it given how well it runs and how easily it starts.

My 350, the poor running car, is having its head pulled THIS VERY NIGHT! So I will know what to do, and where to go from there.

t walgamuth · #4 03-27-2006, 10:58 PM

wrong with the thought process you are following at 1000 including some repairs.

otoh if it is that cheap it must have a bent one already. or some other major issue.

tom w

bhatt · #5 03-28-2006, 06:58 AM

Must have mislead you guys on the price....

I'd have $1000 that I couldn't recover into the car (taxes, couple of repairs, etc.)

The price on the car is about $10k CDN (Say $8500US or so).

I was just saying that I would only be out about $1000 if the worst case scenario happened (found the rods started to bend after 1 month and sold it a month later for example).

Thanks for everyones comments so far.. very helpful!

t walgamuth · #6 03-28-2006, 07:49 AM

i was wondering how it could be so cheap!

i have the 90 350sdl. i bought it with knowledge of a bad head gasket for $4000. after repairs including lots of valves and such i have about 7500 or so in it. so i am prob ok so far. if it bends a rod i will prob rebuild with a 3.0 liter block since they dont bend rods. then i would have more than it is worth in it but i would have a new motor, too.

i might have a problem paying that much for one unless it had a new long block. or short block.

tom w

dieseldiehard · #7 05-06-2006, 09:08 PM

In a recent eBay listing I found a very well prepared descripotion of the rod bender issue:

"The Engine
When Mercedes re-designed the engine in the model year previous to mine, it started out as a 300SD (3 liter) Diesel engine. -- In an effort to upgrade the engine to a 3.5 liter,(350SD) they didn't strengthen the piston rods and increased the displacement (leaving less room between cylinders) With the heavier forces in the newly 'bored-out' and larger cylinders - the piston rods failed. Usually in the #1 cylinder first. These failed rods caused piston failure which in turn caused the cylinder to go 'out-of-round'. Oil goes up past the rings, unburned fuel goes down past the rings. Oil consumption increases, engine oil becomes diluted with diesel, further exacerbating the entire process.
Sure enough, right around 80,000 my tech suggested an oil consumption test and found that we had one of the faulty engines. Thank God for that Tech and the integrity of Mercedes - - they put a whole new engine in --at NO charge!! I have been humming along ever since - for about 145,000 miles now! These new and improved engines have gone for 500,000 miles. ---I think this car is one of them. Thanks again---Good luck!"

Please note that I have no interest in the car listed, just the fact that the seller's understanding and description of the real problem. The car has a supposedly new engine. It might make a nice car for someone. Not me though, I like the 124 chassis with the 603 diesel turbo. the 140 has way too much stuff to go wrong
DDH
Ebay listing is here:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=4637892880
After the sale is completed and the link is dead I'll try to remember to remove the link but the words should be left for others to read, don't you agree?

lkchris · #8 05-07-2006, 11:52 AM

Once an engine has started bending rods there is no notice because it already has.

Brian Carlton · #9 05-07-2006, 12:22 PM

Neil,

Ask the seller what the current oil consumption rate is........he'd have to know that.......unless it's a dealer.

If the consumption is less than 2K to the quart, them buy it.

Watch the consumption carefully. Once it gets to 1K to the quart........then sell it.

If you buy it and it consumes oil at a rate of 1K to the quart......personally......I'd sell it immediately.