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tommcat
08-21-2011, 04:33 PM
97 prostar 205, LT-1. my oil pressure sending unit just went, it shows full pressure all the time, even with the engine off. does anyone know if it is just a normal GM sender i can grab at napa or is it something different for the boat?

tom

Jeff d
08-21-2011, 04:45 PM
I got one from NAPA for my LTR and it works fine (Part # SME 185899):
https://www.napaonline.com/Catalog/CatalogItemDetail.aspx?A=SME185899_0134690215&An=0

That's a Sierra "marine" sender though and they had to request it from another store about an hr away. They had it the next morning for like $37 w/ tax. I'm pretty sure just about every pre '06 marinized Ford or GM smallblock uses the same sender. My guess is that there's a cheaper "automotive" one that would work just as well for less money and immediately available but they wouldn't have accepted a return since it's an electrical component. The guy there said that some marine gauges are reverse of auto gauges (i.e. more resistance=less pressure or vice versa). Not sure how true that is but I just went for the marine one to be safe.

You could also get what appears to be the same part from Skidim for the same price (+shipping but -tax unless you live in SC):
http://www.skidim.com/prodinfo.asp?number=R020001

Jeff d
08-21-2011, 04:51 PM
BTW my factory sender had a square profile vs. the angled top on the Sierra part. The factory one was painted black rather poorly so I painted the new one black too even though it appeared to be plated in some kind of corrosion resistant metal. It was as easy to change as a sparkplug and works fine. Before I had oil pressure readings all over the map. I'd be idling and it would jump up to 70-80 psi. I wouldn't touch the throttle and it would drop back down to like 10 psi. The new sender cleared all of that up and if I remember correctly it's like 40-50 at idle and 60-70ish under throttle with a smooth progression as load/revs increase.

tommcat
08-21-2011, 04:55 PM
it is definitely a high resistance=low pressure reading type

Jeff d
08-21-2011, 05:04 PM
it is definitely a high resistance=low pressure reading type

Good to know.

I had my suspicions that a standard $15 80 PSI sender would have done the job but maybe those are reversed.


The parts store websites didn't go into that much detail on their universal senders. At that point I gave up on trying to save $15 and bought the Sierra one. IIRC I had to do a couple of cross references from the part # stamped on my OEM sender to arrive at the Sierra part above.

Skipper
08-21-2011, 05:13 PM
BTW my factory sender had a square profile vs. the angled top on the Sierra part. The factory one was painted black rather poorly so I painted the new one black too even though it appeared to be plated in some kind of corrosion resistant metal. It was as easy to change as a sparkplug and works fine. Before I had oil pressure readings all over the map. I'd be idling and it would jump up to 70-80 psi. I wouldn't touch the throttle and it would drop back down to like 10 psi. The new sender cleared all of that up and if I remember correctly it's like 40-50 at idle and 60-70ish under throttle with a smooth progression as load/revs increase.

I have recently noticed that my oil pressure is running in the 60-70 range under throttle. I never noticed that before. I throught it was in the 40-50 range. Even after an oil change I have the same increased psi. The guage is not jumping all across the board, but it looks like it might be worth the time and money to replace the sending unit?

Opinions?

tommcat
08-21-2011, 05:21 PM
jeff, i'll be picking up that napa sender from your post tomorrow, thanks for the info

Jeff d
08-21-2011, 06:01 PM
I have recently noticed that my oil pressure is running in the 60-70 range under throttle. I never noticed that before. I throught it was in the 40-50 range. Even after an oil change I have the same increased psi. The guage is not jumping all across the board, but it looks like it might be worth the time and money to replace the sending unit?

Opinions?

I'm not 100% certain of the numbers I posted above with the new sender. I'd have to pay closer attention and make a note next time I'm out. The sender is just FYI for the operator and if I'm not mistaken the ECU doesn't ever "see" the data from it. There's an oil pressure switch (usually on the opposite side of the engine) that the computer "listens" to. I think it's a basic on/off if the pressure is correct vs. too low. This would be the sensor that would actually throw an error code via the ECU putting you into "limp mode". Not sure if it's just a low pressure switch or a high/low pressure switch. Anyway, if you're not getting a check engine light along with the seemingly elevated pressure I think you're OK as long as it's not pegged out at 80 all of the time. The pressures you posted sound OK compared to what I've been seeing.

I'd confirm that your oil is not overfilled. Also, I think a stuck/restricted PCV valve can cause elevated oil pressure but I could be wrong. They're like $4-5 at any auto parts store and a good preventative maintenance item anyway. Just pull your old one and go match it up with an appropriate new one. Also, when you changed the oil did you use the same weight (i.e. 15w40) that you'd been using previously? A different weight could cause variation in pressure levels at a given RPM.

Skipper
08-21-2011, 06:03 PM
Thanks. I always use Rotella T 15W40 oil and the NAPA 1060 filter. No difference there. I don't think I have replaced the PVC valve this season. I'll try that. Thanks.

rem_pss308
08-21-2011, 07:54 PM
You have to make sure its a marine sending unit. I tried a standard sending unit and it wouldnt work.

JimN
08-21-2011, 08:04 PM
You have to make sure its a marine sending unit. I tried a standard sending unit and it wouldnt work.

That sender came from GM when Indmar received the engine. I can't think of a single reason it would need to be a marine-specific unit. Did you see a part number on the OEM part?

rem_pss308
08-21-2011, 08:34 PM
Dont know JimN could have been a faulty sending unit. But after I got one from a marine dealer. it worked. This was on my 1993 with the 351 carbed motor.

sp00ky
08-22-2011, 11:35 AM
I had the same issue. Replaced the sending unit from skidim.com. I put the new one on and it did not fix the issue. I am going to rewire next.

tommcat
08-22-2011, 11:37 AM
did you test the gauge to make sure it even moves? it should read 0 with the sender unhooked and max with the wire grounded, that at least lets you know if the gauge or wires are completely open or shorted.

JimN
08-22-2011, 11:54 AM
I had the same issue. Replaced the sending unit from skidim.com. I put the new one on and it did not fix the issue. I am going to rewire next.

You want to rewire it, but you don't know the cause of the problem. That makes no sense, whatsoever. FIND THE CAUSE! Test the wire- short the wire to ground and see if it pegs the needle. If not, test the gauge. If you short the sender wire at the gauge and the needle does nothing, make sure the ground or B+ wire is good. If that doesn't help, you have a bad gauge.

Diagnostics isn't guessing, unless it's an educated guess. It requires logical thought, knowledge of how it's wired and how it's supposed to function. If you don't know, buy a manual- this is a car/truck engine, after all.

Sorry if this seems harsh but replacing the sender and then deciding that the wire needs to be replaced is an awfully simplistic way to find the problem. It could be a bad terminal on the wire, at either end. It could be a loose nut on the gauge. Measure the resistance between the sender and gauge, then find the problem if the resistance is high.

tommcat
08-22-2011, 01:02 PM
Diagnostics isn't guessing, unless it's an educated guess. It requires logical thought, knowledge of how it's wired and how it's supposed to function. If you don't know, buy a manual- this is a car/truck engine, after all.

.i get that same type of thinking in the automotive field jim. people want us to swap parts for them all the time, or i get their vehicle after they've already replaced every part they could think of and now finally want it diagnosed since none of that fixed it.:rolleyes:

tommcat
08-24-2011, 07:49 PM
well i got the boat started today and although the oil gauge works it's not accurate. pretty sure the gauge is junk, the sender reads the correct resistance and the wire is not shorted or open. only problem is i cant seem to find anyone offering the gauge anymore. does anyone have a link for them?

tommcat
08-25-2011, 08:18 AM
well i couldnt find an exact mastercraft gauge but the teleflex 'eclipse' gauges are pretty close so i ordered one, we'll see how close it is when it gets here.

for anyone elses reference, here is the diag steps for the gauge/sender

To test the gauge, voltage from "I" to "G" terminal must be 10-16 volts DC, with no wire on "S" terminal. Gauge pointer should rest below the "0 PSI" mark. Next, connect the "S" terminal to the "G" terminal (leave "I" and "G" terminals connected). The gauge pointer should rest above the maximum pressure mark.
Sender resistance can be measured to determine the sender's correct operation. Remove wire to gauge. Connect an ohmmeter to terminal of sender and to engine block. Approximate pressure sender resistance values are:
Zero pressure = 240 ohms
1/2 gauge reading = 103 ohms
full gauge pressure = 33 ohms.
You will get half these values on a dual gauge sender.
If sender is shorted (0 ohms) gauge will read above full gauge pressure reading.
If sender has infinite resistance (open) gauge will read below 0 PSI.
If gauge reads lower than expected, was sealer used on the sender threads? (See illustration.)
The accuracy of the system (gauge & sender) can be 5 PSI at 40 or 50 PSI.
Use of pipe extenders to plumb both a sender and pressure switch (for horn or warning light) from one port is not recommended. Pressure readings will be accurate, but the weight added to the extended fitting of a vibrating engine may cause fatigue related break age.
Teleflex does not offer senders for metric threaded ports.
Dual Station installations:
When replacing one gauge in a two station installation, the second gauge may need to be replaced as well.
Mixing two gauges from different manufacturers to one sender may cause an error in both gauges.
If one gauge fails the second gauge will read much higher than expected.
If sender fails "open", both gauges will read below the "0" mark.
If sender fails "short", both gauges will read above the "full pressure" mark.
Twin engines: it may be helpful in troubleshooting to switch either the senders or the gauges from engine to engine.

http://www.jamestowndistributors.com/userportal/document.do?docId=835&title=Troubleshooting+Teleflex+Oil+Pressure+Gauges +-+Inboard+%26+Stern+Drive