6.2 / 6.5 Engines

[dieseldriver]

Here's a question from a new diesel owner. I bought a used 1991 GMC diesel pickup. The engine appears to have been rebuilt / replaced sometime in the past. How can I tell if it's a replacment engine and or a 6.2 or 6.5 ? It's a NA engine. Thanks Dieseldriver

[Robyn]

Look at the very back of the engine (Bell housing flange) below the Oil pressure switch.
There are numbers there. A little wiggling and a good flash light and you should be able to see them.
If the number ends in 506 it's a 6.5 if it ends in 599 it could be either as the 599 block was used in the late 6.2's as well as the early 6.5's

Without measuring the bores its really tough.

Another way would be to remove the lower bell housing cover and look up at the rear main seal.
If it has a one piece ( Large round seal) it's most likely a 6.5 I dont think any 6.2's were made with the one piece rear main seal.

The two engines are virtually interchangable and get swapped a lot.
The final years of 6.2 trucks saw a lot of N/A 6.5's used as replacement engines.

The GoodWrench crate engines could be used to replace either application.
The only difference was the Van application which used different heads and turbo mount ect.

Good luck and I hope this helps

Robyn

[arveetek]

.

Another way would be to remove the lower bell housing cover and look up at the rear main seal.
If it has a one piece ( Large round seal) it's most likely a 6.5 I dont think any 6.2's were made with the one piece rear main seal.

Robyn

The 599 6.2L blocks have a one-piece rear seal. So, a one-piece rear seal only lets you know you have a later ('92+) block.

If you have a 599 block, the only way to tell if it's a 6.2L or 6.5L is to measure the cylinder bore!

Casey

[john8662]

You can tell from the front of the engine too.

6.2L (up to 91) will say "6.2L D" on the block below where the alternator is mounted, will be nearest to the timing cover.

6.5's all say "GM LD"

6.5 = GM (General Motors) LD (Lousy Diesel).

Ok, ok, it's probably really Light Diesel.


But, if you got "GM LD" then you need to check out the casting number stuff mentioned above, cause that'll tell you which 6.5 you have, or if it's a 599, which (again mentioned) could be 6.2L.

You also can't tell the difference between a 6.2 and 6.5 in n/a when they both have the newer (88+) heads on them (changed injector angle, sound different too).

cheers.

J