Oil Pressure Sender

Carl Stouffer

Carl Stouffer

Well-known member
Jan 15, 2009
4,688
380
83
Tucson, Arizona 85718
We just completed a 3361 mile, 3-1/2 week trip from Tucson up through the Grand Tetons, Yellowstone, Devil's Tower, Rapid city and associated
attractions, then back down through Wyoming and Utah to Tucson. I had no problems with anything on the coach but I was concerned abut my oil pressure
readings on the factory gauge. It never went below the low line (about 1/4 of the way up) and was always higher than that at any speed above idle,
but it was all over the place while driving.

The engine has about 12,000 miles on it (now) and used about 1 pint of oil during the entire trip. The trip included SEVERAL 6 - 8 % grades for miles
and miles in second gear and topped out at over 9600' elevation. All this while towing a 2003, four door Tracker (~3000#)

My dream is to someday go with a Mac-Dash and have a REAL oil pressure gauge among other things, but for now I would like to get the most accurate
reading out of my stock gauge. If I remember correctly, the sending unit comes in two versions, a 60 ohm and a 90 ohm. Which one provides the most
accurate reading on the gauge? I currently have a 60 ohm and don't trust it to be reading correctly.

Thanks.

--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member
 
As cheap as aftermarket oil gauges are go ahead and put one in. It can be
set below the dash or in the dash or wherever.

Its cheap insurance.

Sammy

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On Sat, Oct 3, 2020 at 10:54 PM Carl Stouffer via Gmclist <

> We just completed a 3361 mile, 3-1/2 week trip from Tucson up through the
> Grand Tetons, Yellowstone, Devil's Tower, Rapid city and associated
> attractions, then back down through Wyoming and Utah to Tucson. I had no
> problems with anything on the coach but I was concerned abut my oil pressure
> readings on the factory gauge. It never went below the low line (about
> 1/4 of the way up) and was always higher than that at any speed above idle,
> but it was all over the place while driving.
>
> The engine has about 12,000 miles on it (now) and used about 1 pint of oil
> during the entire trip. The trip included SEVERAL 6 - 8 % grades for miles
> and miles in second gear and topped out at over 9600' elevation. All this
> while towing a 2003, four door Tracker (~3000#)
>
> My dream is to someday go with a Mac-Dash and have a REAL oil pressure
> gauge among other things, but for now I would like to get the most accurate
> reading out of my stock gauge. If I remember correctly, the sending unit
> comes in two versions, a 60 ohm and a 90 ohm. Which one provides the most
> accurate reading on the gauge? I currently have a 60 ohm and don't trust
> it to be reading correctly.
>
> Thanks.
>
>
> --
> Carl Stouffer
> '75 ex Palm Beach
> Tucson, AZ.
> Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive,
> Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American
> Eagles,
> Solar battery charging. GMCSJ and GMCMI member
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
> We just completed a 3361 mile, 3-1/2 week trip from Tucson up through the Grand Tetons, Yellowstone, Devil's Tower, Rapid city and associated
> attractions, then back down through Wyoming and Utah to Tucson. I had no problems with anything on the coach but I was concerned abut my oil
> pressure readings on the factory gauge. It never went below the low line (about 1/4 of the way up) and was always higher than that at any speed
> above idle, but it was all over the place while driving.
>
> The engine has about 12,000 miles on it (now) and used about 1 pint of oil during the entire trip. The trip included SEVERAL 6 - 8 % grades for
> miles and miles in second gear and topped out at over 9600' elevation. All this while towing a 2003, four door Tracker (~3000#)
>
> My dream is to someday go with a Mac-Dash and have a REAL oil pressure gauge among other things, but for now I would like to get the most accurate
> reading out of my stock gauge. If I remember correctly, the sending unit comes in two versions, a 60 ohm and a 90 ohm. Which one provides the most
> accurate reading on the gauge? I currently have a 60 ohm and don't trust it to be reading correctly.
>
> Thanks.

Carl,

As nearly as I know, all the sensors used by GM during the coach time were 90Ohm (FS). If you change to one of that scale. the indication should be
higher.
one of things I don't like about the Delco instruments of that period is that higher resistance is higher indication. For lube oil pressure and fuel
level, this is not so good.

A pint in 3200+ miles is almost too good. With the design of out engines, I would expect more like a a quart plus. It may just be that who ever
honed the bores did a real good job of both round and the correct platue (surface).

Matt
--
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
 
Thanks Matt, That's what I was thinking. The actual oil use may have been more along the lines of a quart. The last time I checked it (400 miles
ago) it was on the high side of between the lines. I had poured half a bottle into it at about the 2000 mile mark.

The machine work was done by a very reputable local shop who has lots of experience building marine 455s and performance engines in general. My
mechanic friend, who assembled it for me, is very anal and paid attention to details (ring end gap, etc) that I might have let slide if I had done it
myself. I am happy with the results. The main bearings are set up a little on the high end of the clearance limits due to the large main journal
size and the shop recommended 20W50 oil, which is what I usually run. For this trip, I had switched to Rotella 15W40 since I knew we were going into
colder country than I usually drive in. The oil pressure was slightly lower than usual, but like I said, it was all over the place on the gauge.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member
 
Erratic readings are often poor connection at the pressure sender tab to wire end connector. The days before weatherpak sealed connections.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
On a subject of Oil Pressure sender - I have a Digi-Panel in my coach. I noticed that Oil pressure reading on it stays at 50 PSI when engine is off.
I don't believe it fluctuates when engine is running too (it used to...). My suspicion is - ether a short in the system, or an oil pressure sender
that has gone bad. Does anyone know the correct part number we need to make it work in the right range?
--
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
 
I agree with John.
I have had similar experience as the connector is not that positive.

On Sun, Oct 4, 2020 at 8:21 PM Vadim Jitkov via Gmclist <

> On a subject of Oil Pressure sender - I have a Digi-Panel in my coach. I
> noticed that Oil pressure reading on it stays at 50 PSI when engine is off.
> I don't believe it fluctuates when engine is running too (it used to...).
> My suspicion is - ether a short in the system, or an oil pressure sender
> that has gone bad. Does anyone know the correct part number we need to
> make it work in the right range?
> --
> Vadim Jitkov
> '76 Glenbrook 26'
> Pullman, WA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.gmcrvparts.com
1-800-752-7502
 
Vadim,
Check your connection at the oil pressure sensor. If it is good, then try grounding the connector with a jumper wire... if the pressure reading on
the Digipanel drops to zero, then you have a bad sensor. If it stays high, then you have an open in the wiring to the sensor.

The sensor wires on the DigiPanel are small, like #22. The internal wire can be broken by the crimp on the connector but the plastic insulation holds
the wire in place. Give the connector a tug on the wire to be sure the wires are not broken. If they are broken, the wire insulation will stretch and
the connector will fall off.

You didn't mention what the stock dash oil pressure gauge reads... I'm guessing it reads OK? There was an option on the DigiPanel to just tap into
the existing sensor rather than add a second sensor.

I was able to add the second sensor with just one fitting:
http://www.gmcmhphotos.com/photos/misc/p63220-mounting-dual-oil-pressure-sendors.html

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
To All,
The original oil pressure sender is an 0 - 80 PSIG unit. So it means that at mid scale your indicating 40 PSIG on your stock dash oil pressure indicator. I have an aftermarket McNeil Dash and the gauge for oil pressure is 0-80 PSIG. If you also have a Digi Panel then the unit will be a 0-80 PSIG when using the factor pressure sender and you can tap in.

Some owners have substituted a 0-60 sender when the oil pressure was down to 30 psig or less. I do not recommend this as this low pressure indication may point to a serious engine issue and you should look into was is causing the situation. Especially if this is the cold oil pressure. Some rules of thumb say that all you need is 10 psig for each 1000 rpm and 30 PSIG oil pressure leaves no margin for safety.

I have a long list of available senders that are available but I will only list a NAPA numbers that I know are the 0-80 units.

Napa OP6638 & OP6638SB

I also have a 0-100 PSIG pressure gauge mounted along side the pressure sending unit on top of the engine. I can always check the gauge to verify the dash indication.

And now a word to the GMC’ers who are not a member of GMCMI. You would be able to find these part numbers and more in the literature that you receive several times each year, JOIN its worth the money! You don’t have to be a member any more of FMCA to join. A lot of local clubs have also elected not to be a chapter of FMCA too.

Regards,

J.R. Wright
GMC Great Laker MHC
GMCGL Tech Editor
GMC Eastern States Charter Member
GMCMI
78 GMC Buskirk 29.5’ Stretch
75 GMC Avion (Under Reconstruction)
Michigan

>
> Vadim,
> Check your connection at the oil pressure sensor. If it is good, then try grounding the connector with a jumper wire... if the pressure reading on
> the Digipanel drops to zero, then you have a bad sensor. If it stays high, then you have an open in the wiring to the sensor.
>
> The sensor wires on the DigiPanel are small, like #22. The internal wire can be broken by the crimp on the connector but the plastic insulation holds
> the wire in place. Give the connector a tug on the wire to be sure the wires are not broken. If they are broken, the wire insulation will stretch and
> the connector will fall off.
>
> You didn't mention what the stock dash oil pressure gauge reads... I'm guessing it reads OK? There was an option on the DigiPanel to just tap into
> the existing sensor rather than add a second sensor.
>
> I was able to add the second sensor with just one fitting:
> http://www.gmcmhphotos.com/photos/misc/p63220-mounting-dual-oil-pressure-sendors.html
>
> --
> Bruce Hislop
> ON Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> My Staff says I never listen to them, or something like that
>
 
I forgot to mention that the wire to the pressure is an 18 ga wire, probably the smallest size wire used in the GMC Coach. Most are 14 & 16 ga wires with a number of 12 ga and 1 or 2 10 ga in the Alternator circuits. If you look at your wiring diagrams the wire size is listed on most of the wires if not all of the wires. 20 ga wires are used in a lot of the wiring in todays modern car wiring as they are not used for load carrying capacity. Most 20 ga wire controls relays and signals to the computer. The wiring diagrams are available on bdubs web site. http://www.bdub.net/GMCLinks.html

The manuals are located here:

http://www.bdub.net/manuals/index.html

Regards,

J.R. Wright
GMC Great Laker MHC
GMCGL Tech Editor
GMC Eastern States Charter Member
GMCMI
78 GMC Buskirk 29.5’ Stretch
75 GMC Avion (Under Reconstruction)
Michigan

>
> Vadim,
> Check your connection at the oil pressure sensor. If it is good, then try grounding the connector with a jumper wire... if the pressure reading on
> the Digipanel drops to zero, then you have a bad sensor. If it stays high, then you have an open in the wiring to the sensor.
>
> The sensor wires on the DigiPanel are small, like #22. The internal wire can be broken by the crimp on the connector but the plastic insulation holds
> the wire in place. Give the connector a tug on the wire to be sure the wires are not broken. If they are broken, the wire insulation will stretch and
> the connector will fall off.
>
> You didn't mention what the stock dash oil pressure gauge reads... I'm guessing it reads OK? There was an option on the DigiPanel to just tap into
> the existing sensor rather than add a second sensor.
>
> I was able to add the second sensor with just one fitting:
> http://www.gmcmhphotos.com/photos/misc/p63220-mounting-dual-oil-pressure-sendors.html
>
> --
> Bruce Hislop
> ON Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> My Staff says I never listen to them, or something like that
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
I like the 0-80 psi sender. On cold start up it reads 3/4 which is 60 where the oil pump bypass is set. After warm up it reads center (40 psi)
running down the road and of course not running but key on reads 0. It is a quick check and the sender is OK.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
> Vadim,
> Check your connection at the oil pressure sensor. If it is good, then try grounding the connector with a jumper wire... if the pressure reading
> on the Digipanel drops to zero, then you have a bad sensor. If it stays high, then you have an open in the wiring to the sensor.
>
> The sensor wires on the DigiPanel are small, like #22. The internal wire can be broken by the crimp on the connector but the plastic insulation
> holds the wire in place. Give the connector a tug on the wire to be sure the wires are not broken. If they are broken, the wire insulation will
> stretch and the connector will fall off.
>
> You didn't mention what the stock dash oil pressure gauge reads... I'm guessing it reads OK? There was an option on the DigiPanel to just tap
> into the existing sensor rather than add a second sensor.
>
> I was able to add the second sensor with just one fitting:
> http://www.gmcmhphotos.com/photos/misc/p63220-mounting-dual-oil-pressure-sendors.html

Bruce,
Thank you for the hint on the stock oil pressure gauge. Totally didn't think about that one. Both Digi-Pannel and stock gauge are running off the
same sensor and both are pinned sky HIGH with ignition ON, engine not running. I checked wiring to both instruments by grounding the wire to engine
and each gauge drops down to Zero when corresponding wire is tested. Looks like its time to go shopping for a sending unit. I'll need to evaluate
space requirements under the hatch to see if I can possibly install two sensors and run them separately - one to each instrument as a means of safety
backup.
--
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
 
The more stuff you “hang” on the live oil feed, the more chance for leak or failure. Then you have the safety device causing the accident. Brass
tees fatigue over time (same issue and reason I don’t hang add on hardware to air bag inputs) Factory gauges have always given me enough info,
instead of a readin not to watch the road.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
Got new sensor. Now everything working as its supposed to. Gauges show 0 PSI with engine off, pressure goes right up to 45-50 PSI when engine
starts. Potential problem avoided. Just out of curiosity, I cut open old sensor (because that's the kind of person I am...). It turns out that the
sweep arm got "welded" to the com bars on the signal side and that's why sensor was always showing high. You can see the black spot on the attached
photo. Don't know what would cause such malfunction. Perhaps age of the sensor? Other ideas?

https://drive.google.com/file/d/1vbDger3fsuG9yt9-HXJr1XKjX5lNNZiS/view?usp=sharing

--
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
 
I drove my coach for 12 years before I cooked a transmission at a bit over
100,000 miles. So, I figured when I replaced it, I would put a Ragusa cast
aluminum finned oil pan on the transmission, along with a 3:70 to 1 final
drive. I modified the cover on the final drive so I could include a sending
unit for a temp gage. The Ragusa pan already has a bung for a sender. I
didn't hook up gages to the senders for a year or so, and made a trip
across Canada and back to Oregon without the gages hooked up. Then, a year
or so later, when we were planning to retrace the Route 66 from east to
west I decided to wire up the gages, along with new eagle wheels fitted
with B.F. Goodrich rubber, and every maintenance item that I could think
of. I hate trouble on the road. Fix it at home, and drive your best parts,
don't carry them as spares. It serves me very well.
Long story short, I found myself watching the hell out of those new
gages, anxious over the readings. If I had never hooked them up, I would
driven along fat, dumb, happy, and oblivious to the temps. Results were the
same. Coast to coast, no problems. But, I don't know how many times I took
my eyes off the road ahead to look at those gages. Way too many, for sure.
Jim Hupy
Salem, Oregon

On Mon, Oct 5, 2020, 8:10 PM Vadim Jitkov via Gmclist <

> Got new sensor. Now everything working as its supposed to. Gauges show 0
> PSI with engine off, pressure goes right up to 45-50 PSI when engine
> starts. Potential problem avoided. Just out of curiosity, I cut open old
> sensor (because that's the kind of person I am...). It turns out that the
> sweep arm got "welded" to the com bars on the signal side and that's why
> sensor was always showing high. You can see the black spot on the attached
> photo. Don't know what would cause such malfunction. Perhaps age of the
> sensor? Other ideas?
>
>
> https://drive.google.com/file/d/1vbDger3fsuG9yt9-HXJr1XKjX5lNNZiS/view?usp=sharing
>
> --
> Vadim Jitkov
> '76 Glenbrook 26'
> Pullman, WA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Simply long term wear. With the arm sitting there for most of its
current-bearing time, continually oscillating a trivial amount, the
contacts simply wore out, IMHO.

Ken H.

On Mon, Oct 5, 2020 at 11:10 PM Vadim Jitkov via Gmclist <

> Got new sensor. Now everything working as its supposed to. Gauges show 0
> PSI with engine off, pressure goes right up to 45-50 PSI when engine
> starts. Potential problem avoided. Just out of curiosity, I cut open old
> sensor (because that's the kind of person I am...). It turns out that the
> sweep arm got "welded" to the com bars on the signal side and that's why
> sensor was always showing high. You can see the black spot on the attached
> photo. Don't know what would cause such malfunction. Perhaps age of the
> sensor? Other ideas?
>
>
> https://drive.google.com/file/d/1vbDger3fsuG9yt9-HXJr1XKjX5lNNZiS/view?usp=sharing
>
> --
> Vadim Jitkov
> '76 Glenbrook 26'
> Pullman, WA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
> Simply long term wear. With the arm sitting there for most of its
> current-bearing time, continually oscillating a trivial amount, the
> contacts simply wore out, IMHO.
>
> Ken H.

Makes sense.

--
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
 
> I drove my coach for 12 years before I cooked a transmission at a bit over
> 100,000 miles. So, I figured when I replaced it, I would put a Ragusa cast
> aluminum finned oil pan on the transmission, along with a 3:70 to 1 final
> drive. I modified the cover on the final drive so I could include a sending
> unit for a temp gage. The Ragusa pan already has a bung for a sender. I
> didn't hook up gages to the senders for a year or so, and made a trip
> across Canada and back to Oregon without the gages hooked up. Then, a year
> or so later, when we were planning to retrace the Route 66 from east to
> west I decided to wire up the gages, along with new eagle wheels fitted
> with B.F. Goodrich rubber, and every maintenance item that I could think
> of. I hate trouble on the road. Fix it at home, and drive your best parts,
> don't carry them as spares. It serves me very well.
> Long story short, I found myself watching the hell out of those new
> gages, anxious over the readings. If I had never hooked them up, I would
> driven along fat, dumb, happy, and oblivious to the temps. Results were the
> same. Coast to coast, no problems. But, I don't know how many times I took
> my eyes off the road ahead to look at those gages. Way too many, for sure.
> Jim Hupy
> Salem, Oregon

Jim, you make an interesting point. At the same time I'm sure you've seen plenty of arguments about how many gauges minimum is required for a good
setup of the GMC coach... Some need few more gauges, some few less, others go bats**t crazy
(https://www.motor1.com/photo/4276473/custom-gmc-motorhome-6x6/). In your case, I would safely bet that you have all your OTHER senses tuned in such a
way, that you'd know your engine is not "happy" without looking at the gauges. Unfortunately, not all of us poses such gifts :)

--
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
 
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