On Aug 20, 2019, at 6:22 PM, tonka6cuda6--- via Gmclist wrote:

> So, with all the cheaper portable units out there has anyone tried recently to install one? What the biggest hurdle....no liquid cooling?

ALL of these machines are 20-25% efficient and the other 75-80% of the fuel's BTU output needs to be discharged quickly and efficiently in order to prevent overheating. Liquid vs. air cooling means absolutely nothing if the thing is crammed into a smallish enclosure with nowhere for that rejected heat to go. The Onans that came stock in our coaches are a pull-through cooling design (Onan's name is "Vacu-flo") that is specifically intended for the RV application and they move 2-3x as much air over the engine and alternator per unit time as compared to a more traditional forced-air cooling that is designed for non-enclosed operation. They expel the waste heat to the side of the coach where convection can take it up up and away - and if you add the Ragusa deflector from our GMC dealers then that heat is all horizontally ejected making for even better cooling.

I follow closely the trials and tribulations of those (especially on fakebook) that get disgusted and throw away their Onan in favor of something they buy at walmart or horrible freight because they think the Onan is junk and something brand new must undoubtedly be better. The usual problem encountered with the newish unit is overheating when trying to run it inside the compartment either while going down the road or while parked with the compartment door up. They simply cannot get rid of waste heat fast enough and subsequently overheat and shut down.

None of what I said addresses mechanical longevity and sound characteristics of the Onan's 1800RPM design vs. the 3600RPM models commonly used as replacements..that is another story. Re longevity: I have worked on a couple dozen Onans in GMC coaches and some of them have been 300-500 hour units and others > 1000 hours. The high time specimens run just as well as the young ones. I have *never* seen an Onan that smoked and puffed and had minimal compression no matter how many hours were on it. I recently obtained a 4kW Powerdrawer that had been abandoned in a horse barn for 25 years and was completely stuck. I managed to free it up but differential compression score was terrible - 80/30 on each cylinder. After a little bit of work on the carb and points I started it up and ran it for about half an hour and now it scores 80/65 on each cylinder and has become my test unit for armature and field assembly repairs. There is no smoke, no oil consumption and it starts every time.

I am aware of several success stories of people (particularly ones here on GMCnet) that have put in other generators and have had positive results - however I also highly respect those particular people's engineering skills and the ability to address the issues.

--Jim
Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH




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The only way to go cheap is to make a carrier and haul a champion generator on your hitch. And even then in some odd conditions it may shut down occasionally when driving down the road.

What you save in trying to install
Something inexpensive, you loose in time. You have to be pretty mechanical
To make another generator work in that compartment.
There are used original gmc onans out there if you look hard that can be bought reasonably.

Give me a call when your in town. 612-961- four-one-nine-six.

Here's how. This in a 23', a 26' has more room to work out baffling and airflow.

http://www.gmcmhphotos.com/photos/g6827-new-genset.html

--johnny