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naughty boy · 03-05-2014, 00:39

Hi everyone, I have a Perkins 4108 in my seamaster 23 cruiser. I have recently had her serviced and fitted an oil pressure gauge and sender. I have discovered that I have very low oil pressure. Idling at about 2 psi, then going up to 20 psi at 2000 rpm and 30 psi at 3000 rpm. No water in the oil, new oil filter fitted. The pressure release valve near filter is clear and working fine. Any ideas?

forsailbyowner · 03-05-2014, 03:21

Mechanical or electric guage? If its accurate something is amiss. I have a mechanical one with the copper tubing kit (instead of plastic). I get 45-50lbs constant, not varying with engine speed. Id check it with another guage, if accurate its not a good thing. Possible causes for pressure that low, bad bearing clearances, pickup tube problems, plugged strainer. Till i found out what the deal was I wouldnt run the engine. Your connection point for the sender/line is near the dipstick?

capt-couillon · 03-05-2014, 06:40

Assuming an electric gauge/sender combination...

Nominal battery voltage is supplied to the + side of the gauge which then runs from the - side of the gauge, to the sending unit and thence to ground. The sending unit ground is typically via the metal body of the unit and the engine block.

The sending unit varies internal resistance dependent on oil pressure resulting in a variable current flowing thru the gauge which provides a calibrated response. The sending units resistance range must be matched to the response curve. If the sender/gauge were not purchased as a set, this may be your problem.

If they were purchased as a set, a poor ground (poor engine block ground circuits are common as well as high ground resistance caused by the use of teflon tape on the sensor threads), high voltage drop on the wire from the sender to the gauge caused by improper wire size or poor connections, or a combination of the two, can cause improper readings. Low supply voltage to the + side of the gauge can also cause low readings.

Mechanical gauges are direct reading through a capillary tube, and are almost foolproof. If possible, beg or borrow a mechanical gauge to temporarily install and check. As stated in the previous post, if your 410.8 is actually running in the range your new system shows, you have issues that need to be addressed immediately.

naughty boy · 03-05-2014, 11:08

Hi all, I have had a gauge put on which confirms the readings I was seeing. Engine out on Monday it is to drop the sump and see what's wrong. Fingers crossed for a blocked strainer. While the engine is out, should I be looking to replace anything else seeing as it's not often I will be able to get to the underneath.

DeepFrz · 03-05-2014, 11:20

You don't say what age or how many hrs. on the engine, however if it were my engine I would be checking the bottom end bearings and replacing the crankshaft seals. Might as well give the bottom end a real good check while it is out. If you find any problems then send the engine to a machine shop to have it rebuilt. Certainly replace the oil pump and clean everything very thoroughly.

If you have a chance before dropping the pan check the compression on all cylinders. Leak down top and bottom tests preferred. That will tell you if the head needs to be removed. If the head needs to be removed then for sure rebuild or new engine replacement.

naughty boy · 03-05-2014, 11:23

No idea of age or hours, it had a part rebuild two years ago by previous owner. Apparently all that he didn't do we're bearings and oil pump. I'm no mechanic so all your post are definitely helping.

DeepFrz · 03-05-2014, 13:02

A partial rebuild could mean just about anything or nothing. If he did a top end rebuild, new pistons, rings, valves etc. then all you need to do is replace the bottom end bearings: rod bearings and crankshaft main bearings and check that the crank is in good shape. Make sure it is not out of round on any of the bearing areas and not worn beyond spec. Have a good diesel mechanic check it out for you and have the crank serviced by a good diesel shop if need be. Then replace the oil pump and screen and all seals and gaskets while reassembling.

Hopefully I haven't missed anything. Others may chime in if I have.

capt-couillon · 03-05-2014, 14:27

Sounds to me like DeepFrz has covered all your bases...

Quote:

Have a good diesel mechanic check it out for you

This is a great suggestion... If you can find a mechanic that is willing to work with you, you have a perfect opportunity to learn about your power plant. The 4108 is about as basic as it gets, and a $100 investment in some basic tools will allow you to do everything not requiring a machine shop.

Do the dirty work yourself (pull the engine, clean and degrease, mount on an engine stand) Then get your mechanic to come in and help with the compression and leak-down tests. While the injectors are out for the compression test, its a good time to have "pop-tested" to check for wear
and proper spray pattern.

After the top end is checked, more dirty work. Flip the engine over, and clean it all up inside. Pull the oil pump strainer and have your mech come back to help "plasti-guage" the rod and crank bearing clearances, plus offer some advice on the results...

Couple of additional suggestions... The 4-108 was (and still is) used in a lot of applications outside the marine environment. Massey-Ferguson tractors, and power plant for over the road reefer trailers are just a couple of examples. Good source for mechanics and parts at a generally lower rate.
Check your local diesel shops for farm equipment and over the road trucks before checking with the "marine" sector. For example your oil pump is a #41314089 (the original was not manufactured by Perkins) and is available from RF Engine for $180 vs $420 from a "marine" supplier... Same pump.
Same advice for having the injectors tested/rebuilt and any other internal engine parts.

Here also is a link to the 4-108 shop manual. Everything you ever needed to know about your iron genoa and how to fix her. Great old beast (ran one for 25 years) Keep oil in her, don't over-rev and she will last you forever.

evm1024 · 04-05-2014, 10:45

Quote:

Originally Posted by naughty boy

No idea of age or hours, it had a part rebuild two years ago by previous owner. Apparently all that he didn't do we're bearings and oil pump. I'm no mechanic so all your post are definitely helping.

Get an il analysis to see what metals are in it. If the oil has been in there a while you might an insight.

**sailorchic34** · 04-05-2014, 17:48

Could be as simple as a bit of trash keeping the pressure relief valve from seating. The relief valve is part of the oil pump assembly on the perkins and accessed after removing the oil pan. I would check that there is no pitting around the relief valve seat. I might even use a small washer to increase spring pressure a tad, which will boost pressure.

Low oil pressure is caused by either a failed relief valve, worn big end bearings, crack in the valve train assembly or wrong oil. Could possibly be caused by a blown head gasket if the oil is fed through the block to the head.

If the engine starts easy and does not smoke then compression is good enough.

LeaseOnLife · 04-05-2014, 17:57

Quote:

Originally Posted by sailorchic34

..
Low oil pressure is caused by either a failed relief valve, worn big end bearings, crack in the valve train assembly or wrong oil. Could possibly be caused by a blown head gasket if the oil is fed through the block to the head.
...

Add to the list: Diesel leaking into oil and lowering the viscosity.

naughty boy · 05-05-2014, 11:25

Update. Engine is out of the boat. Fuel pump is out. The pressure release valve in the fuel pump was jammed open. Looks like this could be the cause. Would this cause low oil pressure?

DeepFrz · 05-05-2014, 11:40

Fuel pump or oil pump? Unless the fuel pump was leaking diesel into the oil sump it would have nothing to do with the problem. I actually didn't know there was a pressure relief valve on the fuel pump, so I think you must mean oil pump. If you really do mean oil pump, then yes, it could be the cause of low oil pressure and you should send manna to the gods.