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Oil Pressure Problem 351w

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    Posted: January-26-2010 at 1:04am
Hi everyone

Just over the last few trips i have had a couple of problems with my oil pressure in my 83SN

its fine for the half hour or so (40psi) then it drops way of to like 5 at idle and 20 running,

the 1st time i saw it i went straight home checked oil level, was a bit low but nothing to cry home about, so i topped it up (15w40), ran it on a hose for about 15 min and everything was normal! so went out again last night and same again after a while it dropped off, not as far as the 1st time but still under 15 at idle and max of 30, everything sounds normal to me no major leeks (always had 1 small one out of the main end seal)

what do u think could be the issue?

the engine has done 1100 hours so its not in mint condition but it starts first pop every time has heaps of power for what i need and i never run it much over 3500rpm in fact most of the time only about 1800rpm.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote SS 201 Quote  Post ReplyReply Direct Link To This Post Posted: January-26-2010 at 8:41am
I am assuming you changed the filter too, If not do so.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SNobsessed Quote  Post ReplyReply Direct Link To This Post Posted: January-26-2010 at 10:53am
Morgan - It sounds to me that your bearings are at the end of their life (too much clearance). You might want to switch to 20W50 for the short term, then start a fund to rebuild the engine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: January-26-2010 at 11:03am
Originally posted by SNobsessed SNobsessed wrote:

Morgan - It sounds to me that your bearings are at the end of their life (too much clearance). You might want to switch to 20W50 for the short term, then start a fund to rebuild the engine.


Or go to a straight weight 40. The pressure dropping off on a high hour engine is typical when using multi vis oil after it gets hot.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote eric lavine Quote  Post ReplyReply Direct Link To This Post Posted: January-26-2010 at 12:13pm
i dont condone Lucas, but it wouldnt hurt....run it in my car to keep the oil pressure light from coming on. thats a mechanics fix btw. I look at it this way its not going to get any better and why spin a bearing and create yourself more problems
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SS 201 Quote  Post ReplyReply Direct Link To This Post Posted: January-26-2010 at 6:08pm
What the Lucas does is keep the viscioty of the oil up. Bearing clearances get bigger and so does the pumps,Heavy oil does help, however its flows heavier so the quality of flow of the oil is comprised a bit that's why they use a multi vis oil.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote behindpropeller Quote  Post ReplyReply Direct Link To This Post Posted: January-26-2010 at 7:55pm
Originally posted by MorganB MorganB wrote:

Hi everyone

Just over the last few trips i have had a couple of problems with my oil pressure in my 83SN

its fine for the half hour or so (40psi) then it drops way of to like 5 at idle and 20 running,

the 1st time i saw it i went straight home checked oil level, was a bit low but nothing to cry home about, so i topped it up (15w40), ran it on a hose for about 15 min and everything was normal! so went out again last night and same again after a while it dropped off, not as far as the 1st time but still under 15 at idle and max of 30, everything sounds normal to me no major leeks (always had 1 small one out of the main end seal)

what do u think could be the issue?

the engine has done 1100 hours so its not in mint condition but it starts first pop every time has heaps of power for what i need and i never run it much over 3500rpm in fact most of the time only about 1800rpm.





Put a mechanical gauge on the engine and verify that you actually have low pressure. 1100 hours isn't much.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote SNobsessed Quote  Post ReplyReply Direct Link To This Post Posted: January-26-2010 at 9:17pm
BP, good point. I once had a loose connection on a sender & the gauge would vary depending on speed (vibration).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MorganB Quote  Post ReplyReply Direct Link To This Post Posted: January-26-2010 at 9:24pm
Hmm Seams everyone has the same conclusion i have come up with, bottom end bearings! can i just replace those? or would it be a waste of time? the engine just runs so happy dont relay wana spend money on complete build, i don't think 1100 was a massive amount of hours. will have to look out for this LUCAS stuff see if i can get it here. also will change to 20/50 see if that helps for now! still got at least another 2 months of boarding to get in this summer!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SNobsessed Quote  Post ReplyReply Direct Link To This Post Posted: January-27-2010 at 1:00am
Check out Jbear jr's post. Sounds like he put new bearings in without much fuss;

lower end rebuild
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kapla Quote  Post ReplyReply Direct Link To This Post Posted: January-27-2010 at 1:03am
1100 is not that much on this engines..mine actually went almost 2k before one of the heads cracked..could have lasted some more time if that didn't happen...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote critter Quote  Post ReplyReply Direct Link To This Post Posted: January-27-2010 at 2:39am
I too would put a mechanical guage on before I tore that motor down. It is too easy to pick up and install a mechanical guage not to verify the suspected pressure drop. Just mount it under the motor cover and check it often to verify your concerns. If the oil pressure is ok on the mechanical guage, then you need to be looking elsewhere.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote eric lavine Quote  Post ReplyReply Direct Link To This Post Posted: January-27-2010 at 10:26am
1100 isnt that much if the oil was changed regularly, its funny sometimes you tear into a 500 hour engine and it looks like 3000, but try the mechanical guage first then decide which way to go.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote skicat2001 Quote  Post ReplyReply Direct Link To This Post Posted: January-27-2010 at 1:40pm
What is standard pressure readings? If I can remeber mine runs at 20psi at idle and above 60-70 while running..
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kapla Quote  Post ReplyReply Direct Link To This Post Posted: January-27-2010 at 3:08pm
In the case he decides to put a mech gauge..were should it be plugged? I guess that will need to put the gauge in place of the oil sender?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote abolton Quote  Post ReplyReply Direct Link To This Post Posted: January-27-2010 at 4:03pm
Did anyone else see the episode of Horsepower TV where the drilled into the oil passage in the back of the block and ran copper tubing up to the front of the block and tapped into the oil passage? They where said the racers do it all the time on the Ford 351's because of week oil at the front end.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: January-27-2010 at 4:37pm
Originally posted by kapla kapla wrote:

In the case he decides to put a mech gauge..were should it be plugged? I guess that will need to put the gauge in place of the oil sender?



either tee into the oil pressure switch/sender or remove it and install the gauge start it up and let it get hot no need to go anywhere to see the oil get hot and loose pressure, Driving it is only going to get it hotter quicker and so it takes an extra couple minutes sitting at the dock or on the trailer to find your answer.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GottaSki Quote  Post ReplyReply Direct Link To This Post Posted: January-27-2010 at 5:05pm
Originally posted by abolton abolton wrote:

Did anyone else see the episode of Horsepower TV where the drilled into the oil passage in the back of the block and ran copper tubing up to the front of the block and tapped into the oil passage? They where said the racers do it all the time on the Ford 351's because of week oil at the front end.


Never heard of any weekness with the W oil system.
And weak at the front? where the pump is? Similary skeptical.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: January-27-2010 at 5:17pm
Originally posted by GottaSki GottaSki wrote:

Originally posted by abolton abolton wrote:

Did anyone else see the episode of Horsepower TV where the drilled into the oil passage in the back of the block and ran copper tubing up to the front of the block and tapped into the oil passage? They where said the racers do it all the time on the Ford 351's because of week oil at the front end.


Never heard of any weekness with the W oil system.
And weak at the front? where the pump is? Similary skeptical.

Im no expert, but I thought I had heard of something along those lines regarding the Ford 460. Maybe thats where the confusion is?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MorganB Quote  Post ReplyReply Direct Link To This Post Posted: January-27-2010 at 7:55pm
Originally posted by eric lavine eric lavine wrote:

1100 isnt that much if the oil was changed regularly, its funny sometimes you tear into a 500 hour engine and it looks like 3000, but try the mechanical guage first then decide which way to go.


Yea we have had the sump off once wile i had the engine out to paint the bilge and my mechanic was quite happy that it was real clean in there and the oil looked good and so on, but once again it hasn't been performing max rpm 4200 (only had it there once, also at that rpm after bout 1 minute i could hear the tapits then it would start to back itself off a bit then eventually blow back through the carb? does anyone know what that could be? (never tried that again happy to keep rpm low wake boarding)

Thanks for the link but does anyone know of a more detailed post on someone pulling the bottom end off with photos and so on?

Thanks for all the responses im getting some good ideas
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Post Options Post Options   Thanks (0) Thanks(0)   Quote critter Quote  Post ReplyReply Direct Link To This Post Posted: January-27-2010 at 10:42pm
This site has some pictures that you can enlarge to get better views.

Rebuild

If you are thinking of only doing the main and rod bearings without pulling the heads, it can be a bit more difficult.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Waterdog Quote  Post ReplyReply Direct Link To This Post Posted: January-28-2010 at 5:11pm
It's tricky rolling the main thrust bearing out of the block and rolling the new one in. The first one I did, a freind gave me OJT on, now I can do it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MorganB Quote  Post ReplyReply Direct Link To This Post Posted: February-02-2010 at 7:41pm
Update:

Put a diff version of that Lucas stuff in, it helped a lot, still only getting about 10psi at idle but 40 wile running so will do me out for the rest of the summer i hope!!!

Once again thanks for all the help!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Greg_SA Quote  Post ReplyReply Direct Link To This Post Posted: February-04-2010 at 2:58pm
Hi,

This last weekend, I noticed my oil pressure had suddenly dropped by about say 15psi (idle or while cruising). It is normally around 30psi idle and 70psi cruising speed).

My oil level was also a bit low (at the add oil mark), so I topped it up (not much was needed to get back to the full mark), but the pressure isn't what it used to be (say 15pis idle and 40psi running). I hope that the very short time the oil level was a bit low couldn't have done damage to something? I'm wondering if the oil markings on my dip stick are actually correct, maybe I have the wrong dip stick (eek).

I'm just wondering what I can check/do:

* Replace oil filter? (in case this has some blockage?)
* Remove and clean the sender unit? Does anyone know what I can clean with? Some alcohol?
* Measure resistance of sender unit (240 ohms = 0psi, 33 ohms = max psi, 100 ohms is about the middle).
* Test with mechanical pressure gauge?

A local mechanic mentioned that it can be the bypass (relief) valve of the oil pump is stuck open (gone sticky)? As I understand, the oil pump diverts oil back to the sump to regulate the oil pressure from going too high.

MorganB, did you try anything listed above, or just run the Lucas oil?

Any help would be great.

Cheers
Greg
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MorganB Quote  Post ReplyReply Direct Link To This Post Posted: February-04-2010 at 9:02pm
Hi Greg no i did not do any of that was always planning on getting another gauge and put it on but were using the boat every second day so have yet to have a chance to do so!

the Lucas seamed to make things abit better to be comfortable running it!!

A little strange that both of us all of a sudden had a problem after letting the oil get a bit low!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SNobsessed Quote  Post ReplyReply Direct Link To This Post Posted: February-04-2010 at 9:11pm
Originally posted by Greg_SA Greg_SA wrote:

Hi,

I noticed my oil pressure had suddenly dropped by about say 15psi


Greg - It doesn't sound like wearout - I'm with you, sounds like the relief valve has dirt in it. Or maybe the oil pump is going out.

How many hours are on your oil change? I notice a drop (but not quite that much) after about 40 hours.

Test with a mechanical gauge before you tear into it!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Greg_SA Quote  Post ReplyReply Direct Link To This Post Posted: February-04-2010 at 10:47pm
Hi,

Thanks for the feedback.

I do my oil change around every 50 hours. It has been about 40 hours since the last change! Maybe I should just do a oil change again, now - it can't hurt?

I'll definitely test with a mech gauge - just need to find one locally (I'll call some auto shops).

Thanks again,
Greg
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Post Options Post Options   Thanks (0) Thanks(0)   Quote critter Quote  Post ReplyReply Direct Link To This Post Posted: February-04-2010 at 10:57pm
Originally posted by Greg_SA Greg_SA wrote:

I'll definitely test with a mech gauge - just need to find one locally (I'll call some auto shops).

Walmart has them along with most Autoparts stores. Just get a cheap one
as you will be removing it after correcting the problem and it will stay in your workbench for the next time you need it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Greg_SA Quote  Post ReplyReply Direct Link To This Post Posted: February-08-2010 at 5:11am
Hi,

I did an oil change (and oil filter) this weekend (the last oil was only 30 hours old). When cold, the oil pressure was around 80psi... and as it warmed up, it dropped to around 55 to 60 psi when cruising. Idle was around 30 (in gear) or 40 (neutral) psi. It stayed like this for around 10 minutes of cruising.

Later the next day, I took a long cruise at say 3000rpm for around 20 minutes... I noticed the oil pressure was a bit lower, around 50 psi.

At idle (neutral) it was 30 psi, but then after idling in neutral for about 2 minutes, it rose to 40 psi. At one point, it was at 50psi after a l0ong time idling.

Could these differences be due to a difference in oil temperature?

I got a mechanical oil pressure gauge, but never got a chance to test it - I'll try next weekend though.

Regards,
Greg


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Post Options Post Options   Thanks (0) Thanks(0)   Quote SNobsessed Quote  Post ReplyReply Direct Link To This Post Posted: February-08-2010 at 10:47am
Greg - Your pressures are very similar to what I get.

I'd say your problem is solved.

The differences in pressure are from the oil temperature changes affecting the viscosity. The oil takes a while to cool down after you go back to idle. Remember the block stays pretty constant from the lake water cooling but the pistons get very hot from the constant load at higher RPMs. The oil cools the pistons off.
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