Anomaly

Wasn't sure where else to put this. Short version, I'm trying to decode an oddball engine serial number of W1N10THS on a 90-degree V-6 engine that found its way into a 1998 GMC Safari van. The serial number was found in the appropriate location, top side of passenger side engine block below the cylinder head.

But W1N10THS doesn't jive with anything that should have been installed in this van, or even anything in the same ballpark. I am not sure this engine is even a truck engine, or that it is even a 4.3. Block casting number appears to be 14099090M, which is interesting, because some sources indicate that casting number as a 2000-2005, others indicate 1998, others indicate 2000. The serial number doesn't jive though.

And here's the kicker -- I have run across another thread elsewhere from someone else, also with a 14099090M block, with a serial number of W10L29THF. So I'm thinking there was a change in serial number structure that came with the 14099090 / 14099090M blocks that hasn't been made common knowledge.

"10" "29" might be October 29th, which would make "1" "10" January 10th. "W" might well be the engine VIN code, as these were both 4.3 V6s, likely W-code (They were coded X, W, and Z). But if that holds water, what do 'L' and 'N' mean? It's not likely to be year of manufacture, because L would be 1990, and N would be 1992. 14099090 / 14099090M blocks were from 1996-on.

Okay, so let's take it from the top to explain how this came to pass and why I am seeking this information.

At one time, I owned an all-wheel-drive 1998 GMC Safari (the Astro's twin brother) that lost oil pressure after never having really shown good pressure to begin with (4.3s usually pull 60-80 cold, 40 warm, this one showed about half that). It was a nice van, fully loaded and I liked it a lot, so I decided to fix it.

However, at 185k, I couldn't be sure whether the engine was worth fixing, so I purchased a used engine / transmission package from a reputable eBay seller, S10Warehouse. The price was fair, the transaction went well, and my merchandise arrived safely, very clean, well-wrapped and complete. No reason to believe any wrongdoing of the seller, and I recommend them if anyone needs anything that interchanges with the S-trucks / SUVs .

I tried out a mechanic that a friend recommended and had been going to for years. They had quoted me $1300 for the job, and I had the van towed there about a week after delivering the engine and transmission, which had come from a 2000 Oldsmobile Bravada (the S-Blazer's luxurious cousin), with 111k miles.

Here's where the trouble (and mystery) starts. The mechanic in question had my van a total of 5-6 weeks. Along the way, he told me he would be out of town for about a week. He never said anything about this when I delivered the van or the engine. I have it on good authority from others who have similar vans that they have changed engines and such within a week.

At some point, I came by to check progress. During that visit, this guy went out of his way to show me how good his full-size pickup ran. Which just happens to be a 4.3L / 4-speed auto / 4WD, same as my van uses. Stay with me, you'll see why this is relevant soon.

When the guy called to say my van was ready a few weeks later, I was charged another $600 for parts that were supposedly necessary to make the replacement engine work with my van's setup. When I started the engine, I noticed no change in oil pressure from before the previous complete loss of oil pressure. It also ran poorly under load. I immediately returned to this mechanic, who blamed it on the 'used' engine and after checking PCM codes, gave me three codes indicating a catalytic converter problem.

Trouble with this is, another mechanic scanned it and gave me a completely different set of trouble codes, and said nothing was wrong with the converter. The problem was found to be damaged wiring on an exhaust sensor (which had not been a problem before it was trusted to the guy who supposedly swapped the engine and transmission).

About 15,000 miles later, the engine was developing a noticeable knock. I parked it and started checking things over, finding a lot of indications that the engine I bought was not the engine that was in my van. There was way too much grime and grease -- the engine I bought was clean enough to eat off of.

There's not a lot of great info on engine serial numbers and such for the 4.3 V6, but a lot of it indicates the serial number should be on the face of the block below the passenger side cylinder head. I found a number there - it appeared to be W1N10THS. Casting number was 14099090M.

Each spot in this number appears to have been made with a series of dots to form a letter or number as needed. I've wondered if it might have been altered, I thought most serial numbers and casting numbers were stamped in such a fashion as the characters would rise above the surface. But apparently one of the two engine plants that built these used such a method of rendering serial numbers.

At any rate, it was so faint that I literally had to wire brush the grime, spray paint the stamping boss, then sand the dried paint away to make the serial number stand out with the remaining paint, just to be sure I was reading it right, because according to what I can find, it does not make sense, because late-model Vortec 4.3s were built two places -- Romulus and Tonawanda, and these serial numbers should start with R or T. Each plant had their own system for the serial number.

For Tonawanda, the first digit is the source code. The second and third digits are the month of build. The fourth and fifth digits are the date of build. The sixth, seventh, and eighth digits are the broadcast codeFor Romulus, the first digit is the source code. The second and third digits are the month of build. The fourth digit is the hour of the build. The fifth and sixth digits are the date of build. The seventh, eighth, and ninth digits are the broadcast code.

W1N10THS is obviously not a correct serial number for the original engine, the replacement I purchased, or anything that should be in this vehicle. It's not anywhere close to being a correct format.

Which leads to my question... What the hell is this serial number, what does it mean, and where did this engine come from? I have a few theories, but I wanted to see if anyone recognizes this serial number and what it might have come from.

The best I can come up with is that it is an earlier non-Vortec 4.3 (my understanding is the Vortec heads and intake can be swapped to non-Vortec blocks if swapped together). Some info leads me to believe that the W in this serial number is Willow Run, the 1 is either January or the 1st of the month, the N could be 1992, being the 14th letter of the alphabet per VIN year coding since 1980, the 10 could be October or the 10th of the month, and the THS seems to be a suffix indicating the engine's application. However, THS comes back as a 1971 307, or a 1982 350, which it obviously is not.

A third-party source claims that THS is for S-trucks and Silverados built in the 1992-1995 era, but hasn't yet been able to get this information to me for review. If this is true, and the N is indeed the 14th letter in the alphabet for 1995, this could very well mean that this engine came out of a 1992 Chevrolet / GMC S-truck or full-size truck -- NOT a 2000 Bravada engine.

So it appears the serial number I found in the appropriate location is bogus, altered, or this is either an older 4.3, or perhaps not even a 4.3, but some other V6 that just happened to be transplantable. I've read that the 265 (4.4L) V-8 begat the 200 (3.3L) V-6, the 305 (5.0L) V-8 begat the 229 (3.8L) V-6, and that the 350 (5.7L) V-8 begat the 262 (4.3L) V-6, which was eventually updated and dubbed the Vortec 4.3.

Seeing as the 4.3 was not just used in trucks, but had a brief run in Malibus, Caprices and Monte Carlos in the mid-80s, I wonder if this is even a truck engine. And seeing as the 200, 229 and early 262 appear to be largely interchangeable, I wonder if this might not even be a 262, but perhaps a 229, or even a 200. It certainly appears that it might be possible to put a Vortec intake and heads on a 200 or 229 if it were tried.

I have also explored the possibility of this being a marine or industrial engine, and found a site for remanufactured boat engines, listing this block casting number of 14099090M as a 2003-2007 design. Other sources list it as 2000, some 1998-2001. The problem is that the serial number does not jive with anything produced in this era.

The 'W' might be 1998 per VIN structure, but what would the L or N in these two serial numbers mean? 'W' could also simply be the VIN's engine code. Can anyone here help figure out this serial number and solve this mystery? Thanks in advance.