Oil pressure reads max when Perkins 4.236 running

[solmaniac]

Is my oil pressure sender malfunctioning? New boat to me. I get maximum oil pressure on the gauge when engine starts and it stays that way. I get 1 ohm reading when testing wire connection to ground. This is all new learning to me. There are two what look like sensors coming off the same tube coming out of the block (picture), only one has a wire going to it, which goes to oil pressure gauge on the instrument panel. There is a wire floating around connected to nothing which leads to an alarm on the instrument panel. I am reluctant to leave engine running when oil pressure gauge doesn't seem right. I'll start thinking about the leaking water pump">raw water pump later. Help!

[deblen]

Workshop manual Perkins 4.236 Workshop Manual


Wiring diagram http://www.cruisersforum.com/forums/...am-107801.html

You have two oil pressure sending units.
The one with the wire removed is for an audible alarm. The sender provides ground when oil pressure drops close to zero. Turn key on-do not start engine.Touch the loose wire to engine block & you should get audible alarm. If this works,touch to alarm sender terminal & you should get alarm.
Turn key off & connect loose wire to alarm sender terminal.
Start engine.Alarm may sound briefly & then stop sounding as oil pressure builds.

I suspect the other sender,which operates the gauge,is defective . Check that the wire to/from gauge is not grounded somewhere in it's travels-not likely because you said that gauge only goes hard up when engine is running. Confirm gauge goes to zero when engine is stopped. If OK,replace sender-make sure you get the gauge type sender-not the alarm type as I believe they are different.

Cheers/ Len

[DougR]

The original sender (blue paint) is a combination pressure/ alarm sender with three terminals. One terminal is for a ground lead, one for a pressure gauge, and the third for an alarm. Without a ground lead installed on the ground terminal it won't function for anything.

The new sender is for a pressure gauge, and was probably installed after a partial failure of the original sender. You can check the wiring for the pressure gauge as described by Deblen in his post. Key on, touch and remove the gauge lead to ground. The gauge should peg when grounded and go to 0 when not grounded. It's also very possible that there is a resistance mismatch between the new sender and the old pressure gauge, and that is causing the behavior of the gauge.

I suggest obtaining a mechanical pressure gauge and installing it in one of the ports currently occupied by a sender. Then start the engine and you will be able to see the true oil pressure condition. If the pressure is within the allowable limits you can safely run the engine.

Then you can address the gauge/alarm sender problem. Either a new combination sender that matches the gauge, or two new senders, one for the alarm and one for the gauge.

DougR

[deblen]

Originally Posted by DougR

The original sender (blue paint) is a combination pressure/ alarm sender with three terminals. One terminal is for a ground lead, one for a pressure gauge, and the third for an alarm. Without a ground lead installed on the ground terminal it won't function for anything.

The new sender is for a pressure gauge, and was probably installed after a partial failure of the original sender. You can check the wiring for the pressure gauge as described by Deblen in his post. Key on, touch and remove the gauge lead to ground. The gauge should peg when grounded and go to 0 when not grounded. It's also very possible that there is a resistance mismatch between the new sender and the old pressure gauge, and that is causing the behavior of the gauge.

I suggest obtaining a mechanical pressure gauge and installing it in one of the ports currently occupied by a sender. Then start the engine and you will be able to see the true oil pressure condition. If the pressure is within the allowable limits you can safely run the engine.

Then you can address the gauge/alarm sender problem. Either a new combination sender that matches the gauge, or two new senders, one for the alarm and one for the gauge.

DougR

Thanks for clarifying that Doug.

/ Len

[sailorboy1]

Both of the boats Ivem owned have had problems with the oil pressure and temperature gauges. On both I started with replacing the senders and in both ended up replacing the gauge itself. Since these need to be matched my recommendation is that you just replace both sender and gauge right off the start and save yourself the trouble.

I would recommend that you check the wires first especially at any harness connection.

[hamburking]

Sorry to be the one to state the obvious...but have you checked the oil? Does it look good (not too black) and filled with the correct amount?

[northwestsailor]

I have a similar set up on my 4-236. The ground lug broke off the original sender and to replace it was like $50. So I just went to the auto parts store and bought a Tee and short stub. Total cost in an expensive spot like Friday Harbor was only about $10. Works fine but was alarming the first time the buzzer went off before cranking. That is one loud buzzer!

[Triumphant]

A lot of the 4236M's are insulated ground (I have been told they were modified for use in aluminium assault crafts) so each gauge/instrument, alternator and starter motor will have a positive and negative running to it to make it works and there should NOT be any current running through the engine.

If your engine is insulated ground, one of the senders in the picture appears to have only one wire so it will not work.

When we bought our boat, both the pressure gauges went to max when the key was turned on due to wiring faults

My 1984 4236M run at just under 60 lbs when warm at cruising revs (1500) and about 45 to 50 on warm idle after a long run

Hope this helps

[solmaniac]

Thanks guys!

I do get an alarm by grounding the loose wire...nothing when connecting to old sensor. Still get infinity reading when touching newer sensor to ground. Appears older sensor malfunctioning...and newer one has no alarm switch...and probably mismatched to gauge?

Stephen

[Tetepare]

I spent years of "free time" (e.g., warm and sunny time) with wiring diagrams, a meter, and whatever friend would help me trying to resolve the same problem.

Then last year I googled the meter, and found a trouble shooting guide for it. In five minutes I had determined, yep, the meter. A week later and $60 and all was good- after years of chasing a non-issue because everybody said "it can't be the meter".

[Lancerbye]

I also have a pair of 4-236s and have a single wire sender and a separate switch on a plumbed tee. I suspect the previous owner had problems with the system and teed in a replacement sender, but since the previous unit was a combination unit(pricey) he opted to replace without removing the old system. You could just unscrew the unused sender and replace it with an oil pressure switch. The gauge operating pressure should be between 45 and 65 psi. If is totally wonky get a real pressure gauge 1/8 in. npt fitting( most common) and put it temporarily in place of the sender. Should be a 100 psi gauge.

[hellosailor]

"Alarm may sound briefly & then stop sounding as oil pressure builds."
I knew a big Pearson where the owner had hooked u one of those big (eight or ten inch) fire bells in the lazarette to make sure he couldn't miss a low oil pressure alarm.


The neighbors really appreciate that when he was departing the slip at o-dawn-hundred to make a tide.(G)


So it wouldn't surprise me to find someone had disconnected an alarm.

[deblen]

Originally Posted by hellosailor

"Alarm may sound briefly & then stop sounding as oil pressure builds."
I knew a big Pearson where the owner had hooked u one of those big (eight or ten inch) fire bells in the lazarette to make sure he couldn't miss a low oil pressure alarm.


The neighbors really appreciate that when he was departing the slip at o-dawn-hundred to make a tide.(G)


So it wouldn't surprise me to find someone had disconnected an alarm.

Oh yeah!! Some of the fishing boats I serviced had those! Just great when I was ready to touch the soldering iron to a pcb.

[deblen]

Originally Posted by Lancerbye

I also have a pair of 4-236s and have a single wire sender and a separate switch on a plumbed tee. I suspect the previous owner had problems with the system and teed in a replacement sender, but since the previous unit was a combination unit(pricey) he opted to replace without removing the old system. You could just unscrew the unused sender and replace it with an oil pressure switch. The gauge operating pressure should be between 45 and 65 psi. If is totally wonky get a real pressure gauge 1/8 in. npt fitting( most common) and put it temporarily in place of the sender. Should be a 100 psi gauge.

Mechanical is best IMHO but don't trust that cheapie plastic tubing they use now. Ask me why mine is piped with 1/4" hydraulic hose. 1/8 copper fittings are very difficult to find.

[Captain Bob]

As the owner of a Perkins sales and service business, we replaced many faulty and/or leaking oil pressure senders (particularly in the 4-108, 4-236, 4-etc and 6-354 engines). They are all the same original units. Previous recommendation to check the pressure with a mechanical gauge is a good one. They are hard to find but a Google search should reveal a source. Mine is an older Stewart-Warner gauge. If the oil pressure tests good, check for a good ground to the gauge and then apply 12 volts with a test lead to the positive pin. If the gauge pegs, it is probably OK. I'll take a bet that this is a faulty sender. It was probably provided by Lucas (the prince of darkness) and that alone could explain it.