Community Forums

paul65k · 06-10-2020, 01:07 PM

So our Onan 7500QD started acting up the other day and I took it in for service. The generator shuts down after 10 - 15 minutes and then gives a Low Oil pressure warning.

We have replaced the Oil Pressure Switch (Sender) and it's doing exactly the same thing.

Shop is telling me that they think it's the controller and they are checking on the price but somewhere between 2500 - 3300 for the new controller.

The generator has ~1900 hours and is almost 20 years old.

Does anyone have any thoughts or ideas.....has anyone run into this??

SteveNSue · 06-10-2020, 01:16 PM

It might be that the oil weight is too low for the heat generated. What weight oil have you been using?

RELHUB · 06-10-2020, 02:02 PM

Quote:

Originally Posted by paul65k

So our Onan 7500QD started acting up the other day and I took it in for service. The generator shuts down after 10 - 15 minutes and then gives a Low Oil pressure warning.

We have replaced the Oil Pressure Switch (Sender) and it's doing exactly the same thing.

Shop is telling me that they think it's the controller and they are checking on the price but somewhere between 2500 - 3300 for the new controller.

The generator has ~1900 hours and is almost 20 years old.

Does anyone have any thoughts or ideas.....has anyone run into this??

Do some research on prices for a controller.
That is a complete rip off $3,300.00 Your repair
shop is WAY out of line with that quote.

How much would a NEW generator cost $6,000.00 ???

paul65k · 06-10-2020, 02:08 PM

Quote:

Originally Posted by RELHUB

Do some research on prices for a controller.
That is a complete rip off $3,300.00 Your repair
shop is WAY out of line with that quote.

How much would a NEW generator cost $6,000.00 ???

so a couple of updates:

Shop hasn’t even looked up the part cost yet he was just ballparking so I’ll be interested to see what they come back with for a hard quote.

In the mean time I called a part manager I know at a Cummins factory store and the retail price of the part is actually a little over $1900 and I can get 10% off that so that is now the worst case.

Secondly the price of a new QD7500 is almost $10k at best price I could find online and $4-5k for a used one on eBay😮

paul65k · 06-10-2020, 02:11 PM

Quote:

Originally Posted by SteveNSue

It might be that the oil weight is too low for the heat generated. What weight oil have you been using?

It is running 10-30. Just serviced it before changing pressure switch and it wasn’t even 90* when they ran it.

crb478 · 06-10-2020, 04:57 PM

I had to put a new controller in my 7.5 Onan QD, and it was right at $1900.00. If you can get 10% off that is better than most people can do. For me it was the cheapest option I had at the time. The Diesel engine I have been told will run for a long time with regular service. My controller also had just over 1900 hrs I believe, and I do not know if it was exercised properly before I owned it however. I did have a couple of generators sold locally that would have cost about the same as my repair, but I also din not know their true condition only that they were running right now.

I now know that I have a new controller and a properly running engine, just have to keep it that way.

paul65k · 06-10-2020, 07:37 PM

Update
Shop ordered the controller from Cummins and wouldn’t let me use my 10%....kinda sucks but when you live in a small town you deal with it I guess��

imnprsd · 06-11-2020, 02:11 AM

Try replacing your corroded coolant Temp Sensor.

And if you have not replaced your belt, now might be the time.

Note: Removing the top cover is a PITA, especially if you do not have a generator side. So I'm wondering... Has any one cut an access hole in the cover so you don't have to remover it and then seal it back up with some super-insulated-tape (12" wide)?

I paid an Onan mechanic $650 to to do this repair and after that I wished I took a closer look at this problem. And the picture of this 2004 belt has racked up 570 hours when I changed it. I figure a new belt will last another 15 years so why chance it?

...But the Onan mechanic removed my gen-set form the frame to replace the belt, but this seemed like "overkill" to me. Maybe because my generator was on a slide-out and he could not resist. ...Then I got a lot of generator noise after the $650 repair, because apparently the genny did not sit bank on the rubber suppression "feet" like it is suppose to and the whole thing rattles!!!

So if there is a way to cut an inspection hole (where you can get to the upper pully nut) without removing the generator off its slideout, it seems to me you can make quick work of replacing the belt that way... and who cares if their is a "patch job" on the back of the generator no-one sees!!!

RichKimball · 06-11-2020, 09:19 AM

Quote:

Originally Posted by paul65k

It is running 10-30. Just serviced it before changing pressure switch and it wasn’t even 90* when they ran it.

I have always used, and I thought was OEM spec, 15w40 diesel oil. Hmmm

My bet it isn't the controller, but the temp sender. Good luck.

RELHUB · 06-11-2020, 09:41 AM

Quote:

Originally Posted by mevman

I have always used, and I thought was OEM spec, 15w40 diesel oil. Hmmm

My bet it isn't the controller, but the temp sender. Good luck.

If this controller cost almost $2,000 dollars,
I sure hope they tested it to confirm it is really the issue.

This is why I can't justify owning anything diesel .
All of the parts are so crazy expensive and most times not in stock.

Our work fleet is all diesel and sometimes we have drivers sitting for 2 days waiting for replacement parts.
Our trucks also seem to have a lot of issues with controllers sounds like the diesel industry needs to make better computers.

Mtn. Lion · 06-11-2020, 05:50 PM

Quote:

Originally Posted by RELHUB

If this controller cost almost $2,000 dollars,
I sure hope they tested it to confirm it is really the issue.

So many "mechanics" use the process of elimination. Buying parts and doing a remove/replace approach. The process of elimination. I am curious if they actually tested the oil pressure before replacing the sending unit. And ordering a $2k controller.

paul65k · 06-13-2020, 05:17 PM

So I am certainly a "Skeptic" but in this case I did see them install the new Pressure sensor (That I purchased from Onan) and did same thing. I also saw them replace the coolant sensor as well before the controller was replaced.

While they were in there I also had the belt changed, which needed it as well.

So other than a radiator we have pretty much changed all the components on this baby.....only $3500 with labor

Oh well no one ever said owning a motorhome was cheap

sledhead · 06-13-2020, 07:39 PM

Make sure the shop tests the oir pressure with a mechanical gauge using the oil pressure port of the engine to verify what the oil pressure actually is before they spend your money. This needs to be done while the engine is running and hot, oil pressure will go down as the engine warms up.

Corc · 06-13-2020, 10:16 PM

Are you sure you are getting low oil pressure code FC2? 10 - 15 min shutdown sounds like bad water temp sender, FC24.

If you do indeed have FC2; have you verified you do have oil pressure?

I would not be jumping into a new inverter/controller without some serious troubleshooting, including finding a shop that can download the control FC history.