Hi, I am curious which engine is better to run on WVO 1991-1995 Ford 7.3 or GMC 6.5? and why?

I can't speak to the GMC but I can tell you my '91 runs really well on just about any blend I put in it. Running 80 WVO /15 diesel / 5 RUG right now and really enjoying the savings.

The Ford 7.3 can be one of two totaly different engines for the years you specify, up through 93 they used the 6.9/7.3L IDI Navistar totaly mechanical diesel engine, 94 on had the much more complex powerstroke 7.3L diesel engine. Not sure, but since the engine change took place over late 93 and early 94 I suspect there could be some overlap as to which engine ended up in which year. Parts for the earlier IDI Navistar engines are WAY cheaper than for a Powerstroke and they seem to handle burning veg or WMO fairly well, at least that is the results of a friend that has been burning a 50/50 cold blend of WMO/diesel for the last 3 years in his 93 IDI Ford pickup, after over 35,000 miles on the blend he finally had to put a cheap $150.00 set of Ebay fuel injectors in the engine but he had already saved over $4000 bucks on fuel.

For heavy hauling, I'd much rather have the 7.3 than the 6.5. The 7.3 has a four bolt block, forged crank, rods and a roller valve train. Cam, pump and other front items are gear driven rather than a timing chain.

The IDI Ford/Navistar engines are pretty tolerant of fuel quality. I'm not however a fan of using veggie oil in diesels though. Torn down several engines that were ruined by WVO getting into the lube oil, starving the oil pump for supply. The engines were 6.2L diesels, which are similar to the 6.5.

For a 1/2 ton truck or a light duty 3/4 ton, the 6.5 is a great engine, but I wouldn't want to use one for heavy trailer hauling. The 7.3 is just a more massive engine with stronger internals.

The biggest issue you have to worry about with the 7.3 is block cavitation or 'block worm'. To stop this from happening, make sure you put a sacrificial coolant additive (SCA) in the antifreeze on a regular basis, NAPA sells this along with the test strips to check for the strength of the coolant protection.

I like the 6.9 because it's a simple engine, much thicker block (no cavitation problems) and has all the roller cam goodies with a gear drive on the front of the engine. With a turbo system set at about 8psi max boost, you'll be able to tow just about anything within reason. If you go with a turbo, make sure you get a pyrometer gauge installed as the pistons will start to take damage at around 1250F, they're aluminum. I usually drive so as not to let the temps get above 1000F for a safety factor. If someone wants to pass, I let them.

On some of the years of 6.5 (pre-1997 ?) there can be problems with blown head gaskets / warped / cracked heads . Also the PMD must be relocated or else . Also, I think that there is some kind of problem that comes up with the optical sensor in the IP using WVO . Do some research here ( "find" ) and http://www.dieselplace.com/forum/index.php on the forums at and www.oilburners.net .

I have both a Standyne based 6.9 and a PSD - which would be the equivalent of the 94.5-95 7.3 in your OP - I assume the 94/95 PSDs were HEUI.

Not having to worry about the shaft in the IP shattering or seizing is really nice - that said an injector job for the PSD is about 2k in parts alone and the 6.9's fuel pump, IP and injectors can be replaced for less than $600.00

Pick your poison

The 7.3 is a rock solid engine. Nothing is perfect but it is one of the best IMO. My 01 7.3 will blow the doors of my old 99 6.5. The 6.5's are notorious for overheating causing cracked block, cracked heads, blown head gasket. That's what happened to mine. Cracked block!! But the parts are cheap compared to the 7.3 & are easier to work on. There are upgrades you can do to reduce overheating in the 6.5 but if you are going to be doing alot of towing I would go with the 7.3 no question.

As far as veg my 6.5 ran very well on it. The IP shaft shearing was on the mechanical DB2 IP( pre 93) & the electronic IP never had that problem. I don't have my 7.3 running on veg but have been reading alot on it & looks to be a great candidate for veg as well. I beleive my 01 is a much different 7.3 then the 91-95 but I still think it is a great candidate.

I really like my 7.3 but it has one of the stupidest thing ever done on a diesel engine, the damn injectors are under the valve covers requiring an electrical harness to be exposed to hot oil, I realize the injectors are oil pressure powered and that is where the oil line are but, GOOD GOD ALMIGHTY! That is the dumbest damn thing I have ever seen.