230 Cubic inch Flat Head Six, also known as L-head.

The 230ci Flat Head Six had a long run in Dodge trucks and cars, it was used as far back as the early 40's as a truck motor, and when the big trucks went to the longer 251 style block, cars got the 230. By 1961 it was all over, most cars and trucks used OHV slant sixes, but as a friend of mine always says, OHV are a passing FAD!

The 230ci flat head six was used from at least 1946 until 1960 in Dodge trucks, though up to 1955 it was only used in the 1 tons, and bigger. The lighter duty trucks used the 218ci flat head six from the early 40s, until 1955. The 230 and the 218 are very similar motors, the main difference being the stroke, if you put a 230 crank and rods into a 218, you will have a 230. Now if you were a flat head expert, you could tell the difference between the 230, and the 218 from small clues on the engines, but for the purpose of this webpage, I will consider them the same for description purposes.

How to ID a 230ci flat head

A 230ci flat head has a 23" long head, unlike the 265/251 which has a 25" long head. Post war Flat Heads generally have the build date cast in just below the distributor, so if your motor is dated after 1955 and has a 23" long head, then it is most likely a 230ci motor. The numbers listed below are a good beginning guide, but as the 23" long block was used for so many years, in so many applications, I do not have a comprehensive listing yet.

If you have any info to share on flat head engine numbers, I would be interested in hearing it, as I would like to create a database off a flat head engine numbers, so a person could figure out what their engine came from if it is not the original one.

Engine numbers

I have done some research on flat head six engine numbers, and I have found some funny things, first, the factory manuals, and the Dodge Truck books that have been written in the last few years all use the same numbering system to tell you what year, and model of truck a motor came from.

This makes sense, as the newer books used the original literature as reference material. I got my information a different way, I went out into the field, and looked at actual trucks. I checked the engine number, compared it to what the books said, and when it did not match I went looking for a reason. Sometimes the engine had been replaced, but I kept getting to many numbers that did not match the books, and yet matched several other trucks of the same year.

For example, the books claim that a 1959 W100 with a 230ci flat head six should have the following number on the engine:

M6 W1-1001 (1001 is the starting number, it would count up from there)

I have found that ALL the 59 Dodge trucks, D100-D300, and W100-W200 equipped with the 230ci flat head six that I have checked, have the following number:

M23 1001 (1001 is the starting number, it would count up from there)

When I also found the 58s that I checked had L23 1001 I figured I was on to something!

So I started to check every 230ci flat head I could find in a 57-60 truck, and I kept finding the same numbers over and over again.

Below I have a chart of what I have found so far.
  What the books claim What I have found in the field.
W100 T500 1001
W200 T502 1001
D100 T534 1001
D200 T536 1001
D300 T538 1001
I do not have enough information for 57 flat heads yet. Please send in your info!
W100 L6 W1 1001
W200 L6 W2 1001
D100 L6DL L01001
D200 L6D2 L01001
D300 L6D3 L01001

All 230 equipped trucks, D100-D300, and W100-W200.

L23 1001

W100 M6 W1 1001
W200 M6 W2 1001
D100 M6D1 L01001

M6D2 L01001

D300 M6D3 L01001

All 230 equipped trucks, D100-D300, and W100-W200.

M23 1001


All 230 equipped trucks,

TP 23 8 3 1001

The number breaks down as T=Truck, P= P series, 23=230ci, 8=Month made, 3= day made, 1001=sequential serial number.

I do not have enough info for 1960 yet, the two motors I have checked that were original did follow the pattern from the books, but did not have a sequential serial number.
Now that you have seen the numbers, and learned about what the numbers are supposed to be, and what I have found the numbers to actually be, you will want to go check your own engine. Look at the pictures below to find your number.
The red arrow shows the location of the engine number, this is on the drivers side of the block, 3-4 inches back from the front of the block, just below the head.
Above you can see the engine number, TP23 (a bunch of junk) I *I8 This means a 1960 Dodge truck motor made on January 18th if the books can be believed.
I am always looking for more information on flat head six engine numbers, so if you have a 57-60 Dodge truck with a 230ci flat head six, please check your number and E-mail me at Thanks!