oil pump

[Ricky Coon]

Hello, glad to be here. I am changing the front crank seal on the timing cover. I figured while i have it apart in might as well put in a new oil pump, truck has 270K miles. I ordered as melling pump M251 appropriate for the year 2003 dodge ram 3500 cummins 5.9
The only problem is my current pump and all associated gears are straight cut gears. The M251 has helical gears. Anyone have an idea as to why the difference. Thanks in advance

 

[JR]

I would call the vendor you bought it from and double check on the part number. I've not been into a CR engine, but I am pretty certain the gears on the 6b (pre common rail) are helical gears. They may have given you a pump for an early 24 valve engine.
I am actually surprised your gears are straight cut. Seems like a step backwards.

 

[jgillott]

In all my years of playing with these trucks, I can't think of one single oil pump failure. I'm sure that there have been some, but it is very uncommon.

Personally, unless you are seeing some issues with your current pump, I'd send the new one back for a refund, button up your truck, and forget about it.

 

[Ricky Coon]

Thanks for the reply. I ordered the pump from Rock Auto. They are certain based on the year the M251 is the correct pump. I went to the melling web page. Their drill down parts finder lead to the same results M251. I called the tech line at melling. The guy said the straight cut gears started on the 2004 model cummins and the model number is M451.

 

[Ricky Coon]

Thanks for the reply, the primary motivation for changing the pump was my pressure while 40+ at speed the idle pressure seems to be going down below 20. could be symptoms of a much larger problem i am sure but the new oil pump seemed an easy attempt at a fix since i was in there anyway (leaky front seal).

 

[jgillott]

Is that pressure as measured by a mechanical gauge or via the factory gauge?

The Cummins pressure sender has always been suspect and I wouldn't rely on the factory gauge.

 

[Ricky Coon]

Good to know jgillott, thanks for the info. Those reading are based on the factory dash gauge. I'll have to have it checked with a mechanical gauge. Thanks again

 

[JR]

Thanks for the reply. I ordered the pump from Rock Auto. They are certain based on the year the M251 is the correct pump. I went to the melling web page. Their drill down parts finder lead to the same results M251. I called the tech line at melling. The guy said the straight cut gears started on the 2004 model cummins and the model number is M451.

I just did a quick search and found this.
Read the description about the gears.

https://puredieselpower.com/dodge-p...ummins-6bt-diesel-oil-pump.html#/product/1914

Normally Rock Auto is pretty reliable but they may be off here.

I agree with Justin, if you are suspect double check with a manual oil pressure gauge. There should be a 1/8" npt plug on the top of the oil filter, that would be the easiest spot (but not the only). At operating temp the minimum pressure for a B series is 10 psi.

 

[Wayne M.]

Good to know jgillott, thanks for the info. Those reading are based on the factory dash gauge. I'll have to have it checked with a mechanical gauge. Thanks again

Hi Ricky and welcome!
Believe me, it was a huge blow below the belt once it was proven to me, but starting in the late ‘90’s, Dodge trucks have a “improvised” oil pressure reading. Do not go by the gauge!
I second reinstalling your original pump and check your readings with a mechanical gauge hooked to the correct port in the block.

 

[Ricky Coon]

that's what ill do...thanks

 

[Joe Mc]

Ricky, I agree with all repliers above and also doubt there's an issue with the stock pump.
BTW: do take a few minutes and create a signature with your truck info so folks don't have to ask "what year, auto or manual, etc." next time you post.

Welcome!

 

[crabman]

When you do hook up a mechanical oil gage, I think that you will be amazed at how high is really is. "Computer says!", which is BS.

 

[GAmes]

Just a heads up, the pressure you get from the top of the filter housing may or may not be accurate. I have a sender installed in the top of the housing and it will peg a 100 psi gauge easily when the oil is cold According to the schematic the port should be regulated but mine isn't. My dash gauge works just fine and will be showing 50-60. As an added note, when I rebuilt my engine I checked the wear on my oil pump (it had 800k on it) and it was still in spec. I've never replaced mine.