I'm not as good as laying things out as some are here, so hopefully you guys'll cut me some slack for tryin'.

I'm looking to replace the OE oil pump on my '97 F-250HD, 5.8L, 351W, Auto Trani, 2wd & 140K miles. It's time for a new oil pan seal, so it was recommended to change the pump proactively - I agree since I don't know how the truck was treated before I got it. (Nice peace of mind while I'm in there.

It's my understanding that the pump on the 351W is already slightly larger than needed (I read that it's also used in Cleveland's, 429 & 460) which I really appreciate. Not much interested in even more than that for my stock truck, because it's worked perfectly as is, for a driver/occasional hauler. If I could see the advantages in my case, then maybe, but I've heard there can be downsides too. Out of my wheelhouse on that one, so I'm playing it safe.

Running a search on Summit for a Melling oil pump, I get options, but I'm not sure where to go from there. They're described as HV pumps - confusing. Mine's standard, but higher volume compared to some, so perhaps it's considered high volume because it's being sold for a 351W engine? And when sold for the larger engine it's labeled as standard? IDK. Maybe you can see where I'm going with this though?

Going with a Melling brand oil pump because it's all I know, I see a M-83 and the M-83HV. Both are listed as a fit for my pickup. The M-83 is Standard Pressure & Standard Volume. The M-83HV is High Volume & Standard Pressure and for this one the description states it'll increase oil volume by 20%-25%. I won't be running high rpm's often, unless I'm pulling something up a hill or getting on it briefly merging onto a Hwy or what-not. So, I doubt my needs surpass the OE pump, I just don't want to end up with a pump that has slightly less volume than the original, because I didn't understand the differences when ordering. (2 Links below.)

The M-83HV HV / Standard pressure is kind of how I would 'describe' my pump, but maybe someone who actually knows a thing or two would say that the M-83 Standard/Standard Pressure is considered the slightly larger pump mine has already? Am I making any sense? Ha! Just hoping you guys could educate me here, trying to get my head around it.

And then how do I know which shaft before ordering?

PUMP OPTIONS: https://www.summitracing.com/search/...s&kr=oil+pumps
SHAFT OPTIONS: https://www.summitracing.com/search/...oil+pump+shaft

 

If your motor has good oil pressure a HV pump doesn't have any added value but does put more load on the OP drive shaft and has greater parasitic loss. When I built my 5.8 what I believe was a Melling HV pump would not fit inside the stock oilpan.. I had to have a little shaved off the base which was easy enough to do at a machine shop but if you don't have access to those tools then you have a problem.

 

I would go with the HV pump
The pressure relief valve will accommodate any unneeded oil pressure cold, and you'll be glad you put it in there when HOT
I'm a big fan of an updated oil pump drive too, so I do both on every rebuild

 

I have my engine on a stand, guess it is recommended to change it out.

Part numbers please.

 

@Conanski So far, I agree about no real added benefits at least for a street driver - if it ain't broke. Should I go with a HV unit, how much did you have to have removed from the base to get the HV pump to fit? How much clearance do I need between the pan and the downspout? And how much parasitic loss do you think we're we talkin'?

@manicmechanic007 originally that was my thinking too. It'd be different if it were a new build instead of 140K, I'd be HV all the way. Not saying I'm against it, just don't know enough to be convinced back when it seems like there's a possible tradeoff. Part of me says more oil in a loser spec engine would be beneficial, while the other side of me says more isn't always a good thing.

Everything's on the line to get this truck back up and running as reliably as it was. So, I'm mostly trying to play it safe for that reason. I have no experience with HV pumps myself, if I change my mind later, I'll change the pump too. Yet, I've never gotten less than 300K+ out of a stock rig with no real problems. I got over 524k out of my GMC, It was super reliable, started at first turn of the key every time hot or cold, (just like this Ford truck did we're talking about now) but it was getting tired, so I finally swapped the engine out after moving to a location where there were bigger hills to take on. Otherwise, I'd have left it alone and kept driving it as it was.

Anyway, here's one thread here, that has stuck with me, particularly the first reply by krewat. Same HV vs. standard volume argument...no solution - Ford Truck Enthusiasts Forums

I DO want to learn whatever I can about HV pumps, absolutely! I'm not opposed to changing my mind to HV, if there are no or very minor downsides that justify it. But my post / thread is primarily trying to ask how to find out or know if a new replacement oil pump has the 'same pressure & volume' specs as the OE pump that came on it?

 

What about where kretwat mentioned the heads flooding with oil. Wouldn't that be a concern with my engine being higher miles?

Same HV vs. standard volume argument...no solution - Ford Truck Enthusiasts Forums

 

The thread you posted has a good discussion about the pros and cons. Only you can decide what camp you want to pitch your tent in.

The oil pump is the first to get lubricated. I would at least take a peak at the gears and most likely use the stock on. I would not purchase a new one for no reason. That money is best put in retirement or your beer fund.

To date, I've never seen an oil pump wear out if the services have been done properly. When I have seen one worn out, there was a lot more bad stuff inside.

 

Thanks Butcher, I plan on sticking with stock, just couldn't understand what standard oil pressure / volume represents when that same pump was used on several engines and how it rated on them in comparison to mine. If it's standard, you'd think there's be a number showing that spec. I've been thinking about that OEM pump too because a man does need his retirement beer money but can't remember how to inspect it beyond obvious wear. I recall needing to check the gaps inside the pump itself with feeler gauges and haven't been able to find any specs on that to do it right. I bought the truck used years ago, I'm diligent on maintenance, not sure how it was treated before, but I suspect it'd spent time sitting between use and has always been dependable for us. I'll be back when it's all said and done and say how it went, for the next guy's research.

 

The way I think of hydraulics is that the pumps never make pressure. They just move the fluid. If the fluid has nowhere to go, the pressure backs up. If there is no pressure relief valve, the pump would no longer turn because something will break.

So, if you got low pressure, the problem is usually there is no restriction. Worn bearings are certainly a good place to check. On a newly rebuilt engine, missing galley plugs is where I would start. Could the pump be so worn that it can't move the fluid to build up the pressure? Sure, but I've yet to see an oil pump that worn out. Can a larger oil pump bring up the pressure? Sure, but you are not fixing the problem, you are just hiding it. That is always assuming that the factory did a good job in the beginning.

If I was putting turbos on the engine or something else that needs oil pressure, I would look at a larger capacity pump. I don't know much about Fords, but what I have looked into, the 351W has a good oiling system.

There are many more people hear that you should listen too.

 

Thanks Butcher, great info!

Yuh know, I was thinking last week the more I learn how these pump works that perhaps (and this goes along with what you're saying too) it's not about what pressure the pump can reach but more about where the cutoff point is for the relief valve that maintains the set pressure, and that might be why I'm not seeing any specs or ratings on the pump's capabilities. That measurement may be considered whatever the overflow valve is, size of the spring, etc? When asking Summit and other reps about it for ordering an oil pump, they all drew a blank. So, I thought, well it couldn't be that simple or surely they'd know. They may've not understood or heard the question so well. IDK