Oil for recently rebuilt 351

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   Hi Everyone,
I scoured the forum for an answer but I came up with nothing on these specific questions.  Please let me know if I missed something.

I just bought an '85 SN2001 that has a recently rebuilt 351 engine (~30 hours).  I've been working my way through some minor repairs that the previous owner said haven't been quite right since the rebuild and I need some advice on an oil pressure issue.

The oil pressure gauge maxes out 80+ immediately after the engine turns over and stays there regardless of engine temp.  I double checked the visible wiring, replaced the portion of the oil pressure sender wire that was hidden inside the conduit for good measure, then moved on to the oil pressure sender.  I took it off, hooked up a manual gauge and sure enough it was the problem.  However, rather than reading the 40-ish psi I expected it started off at 70, creeping down to 60 after the oil warmed up to temp.  I ordered a new sender and while I'm waiting for it to arrive my questions are these:

Question #1: Since the engine is recently rebuilt, is this higher pressure to be expected?  I've read a lot about tolerances being much tighter on rebuilt engines which suggests that this could be related to the sudden change in how leaky the 351 probably was.

Question #2: I'm planning to change the oil before I winterize and my gut is telling me to change to 15w-40 oil like Valvoline Premium Blue to bring the pressure down and prevent any unnecessary problems down the road.  Are there any known issues, long or short term, using this oil in a 351?

Question #3: Am i missing something that I should be checking out before changing the oil type?

Thanks in advance,

-Bryan

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fredJones Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: October-18-2021 Location: Arlington, VA Status: Offline Points: 3	Post Options Post Reply Quote fredJones Report Post Thanks(0) Quote Reply Topic: Oil for recently rebuilt 351 Posted: October-18-2021 at 8:50pm
	Hi Everyone, I scoured the forum for an answer but I came up with nothing on these specific questions. Please let me know if I missed something. I just bought an '85 SN2001 that has a recently rebuilt 351 engine (~30 hours). I've been working my way through some minor repairs that the previous owner said haven't been quite right since the rebuild and I need some advice on an oil pressure issue. The oil pressure gauge maxes out 80+ immediately after the engine turns over and stays there regardless of engine temp. I double checked the visible wiring, replaced the portion of the oil pressure sender wire that was hidden inside the conduit for good measure, then moved on to the oil pressure sender. I took it off, hooked up a manual gauge and sure enough it was the problem. However, rather than reading the 40-ish psi I expected it started off at 70, creeping down to 60 after the oil warmed up to temp. I ordered a new sender and while I'm waiting for it to arrive my questions are these: Question #1: Since the engine is recently rebuilt, is this higher pressure to be expected? I've read a lot about tolerances being much tighter on rebuilt engines which suggests that this could be related to the sudden change in how leaky the 351 probably was. Question #2: I'm planning to change the oil before I winterize and my gut is telling me to change to 15w-40 oil like Valvoline Premium Blue to bring the pressure down and prevent any unnecessary problems down the road. Are there any known issues, long or short term, using this oil in a 351? Question #3: Am i missing something that I should be checking out before changing the oil type? Thanks in advance, -Bryan

MrMcD Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: January-28-2014 Location: Folsom, CA Status: Offline Points: 3764	Post Options Post Reply Quote MrMcD Report Post Thanks(0) Quote Reply Posted: October-18-2021 at 10:20pm
	Well, your high oil pressure will do no damage. It can rob a little horsepower producing the extra oil pressure. If I had my choice between 20 PSI at idle or your 60 PSI at hot idle I would keep your engine just like it is. Someone installed a high volume or high pressure pump in that engine and it is a very common rebuilder upgrade. Since your oil pressure is very strong already I would not choose the 15-40W even though that is my normal 1st choice oil for a flat tappet camshaft with hydraulic lifters. I would switch to a 10-30W that meets the same specs as the diesel oil 15-40W, I forget the SAE spec but you need the extra ZDDP for camshaft protection. I think the 10-30W will drop pressure about 5-8 pounds but I am assuming the engine has heavier weight oil in it right now. Many run 20-50W ;in their boats, there is no telling what you have till you change it.

KENO Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11155	Post Options Post Reply Quote KENO Report Post Thanks(0) Quote Reply Posted: October-19-2021 at 6:52am
	I think you missed the part where you mention what weight oil is in it now Since your gut says to change to 15w40 oil, what's in the engine must be some heavier 50 ish weight stuff like 20w 50 or 15w 50? If these readings are while it's on the trailer warming up on a hose, I'd get the boat on the water driving around so there's load on it and see what the oil pressure reads at different speeds/rpms after it's been loaded for a while You might find that a new sender doesn't fix your issue and that you need a new gauge also, but after the new sender is in, you'll know if that's the case . Also if you have a Pleasurecraft 351, most any High Volume pump won't fit inside the stock (rear sump) oil pan without some serious hammering and banging because it's taller than the normal pump and you can't bolt the pan down.

fredJones Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: October-18-2021 Location: Arlington, VA Status: Offline Points: 3	Post Options Post Reply Quote fredJones Report Post Thanks(0) Quote Reply Posted: October-19-2021 at 9:59am
	Thank you both for your replies Keno, you're right, I didn't mention what weight the oil currently is. Oops. . It's 20w50 right now. I think Valvoline VR1, but not 100% sure on that. You're spot on, it is a PCM 351. The oil pan looks new and hasn't been hammered on so I have no clue if its big enough to accommodate a high volume pump. I suppose I'll find out when I change the oil. The new sender comes today so I'm going to get that installed and see if the gauge is okay. I actually bought a new gauge already but then realized the more likely culprit was the sender and held off on replacing it. Assuming I get the gauge issue worked out today I plan to take her out tomorrow morning to do as you suggested and let the engine fully warm up. The 60-70 was using the fake a lake. Then I'll decide on what weight I should be using. Hopefully my timeline works out because I want to get this figured out before winter sets in. Overnight temps here are getting cold and I probably shouldn't hold off much longer on winterizing. It sounds like regardless of which weight oil I decide to go with, stick with 20w50 or change to 15w40, I won't be doing any harm to anything like the distributor or pump. Is that a fairly safe assumption?

KENO Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11155	Post Options Post Reply Quote KENO Report Post Thanks(0) Quote Reply Posted: October-19-2021 at 1:55pm
	You won't know what you have for a pump unless you take the engine out and drop the oil pan. Way too much work You won't harm the distributor or pump or anything else with either oil, like MrMcD said . Zinc concentration always sneaks into the conversation with flat tappet engines and your Premium Blue being a diesel oil has a decent amount of zinc, and with a little Google magic you can find out how much from the PQIA. They test oils for all kinds of stuff Here's a link to your Valvoline Premium Blue15w40 test results showing plenty of zinc and phosphorus to keep most anybody happy. link You can surf around the PQIA website till your eyeballs and brain are tired of reading about oil, it's a good outfit

MrMcD Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: January-28-2014 Location: Folsom, CA Status: Offline Points: 3764	Post Options Post Reply Quote MrMcD Report Post Thanks(0) Quote Reply Posted: October-19-2021 at 3:23pm
	High volume pumps are a little larger, a high pressure pump is just a higher tension spring in the stock pump.

flyweed Members Profile Send Private Message Find Members Posts Add to Buddy List Gold Member Joined: July-11-2016 Location: WI Status: Offline Points: 546	Post Options Post Reply Quote flyweed Report Post Thanks(0) Quote Reply Posted: October-19-2021 at 8:51pm
	I might add, that before you go "trusting" ANY of your gauges, you check all of your grounds to your instruments, and then upgrade them all to a heavier gauge ground wire and grounding block. Then you can have more confidence in any/all of your gauges.
	'93 Ski Nautique NWZ, Air Boom Tower Drink Tonight..for tomorrow We Ride!

Oil for recently rebuilt 351

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