: mechanical oil pressure gage sending unit location

09-25-08, 12:30 AM
hello all!

kinda new to this place. i own a 1995 cadillac deville concours with the VIN Y northstar engine and recently iv had some problems with the oil pressure sending unit on my car. occasionally i will get a low oil pressure warning and will have to kill the engine to prevent damage. im a little curious tho about whether or not the engine could actually be having oil pressure problems so im kicking around the idea to install a mechanical oil pressure gage into my car.

2 questions

1. where would i install the actual sensor for the gage?

2. is a mechanical gage the best choice for my application?

help on this would be awesome gents!

p.s. this is the first car i have ever bought and i will stand by the fact that i will never buy anything but a cadillac again

09-25-08, 11:41 AM
Plumb the gauge into the oil filter adapter. There should be a plug you can remove and put the fitting in it's place.

Has any recent work been done on the engine? The oil pump is not a common problem on these engines, but it is driven off of the crank shaft snout and if the harmonic balancer is not torqued properly (very tight) it will slip and loose pressure.

09-25-08, 04:50 PM
thanks for the info ranger!

to my knowledge nothing major has been done to the engine it has roughly 98000 miles on it and i bought her off of an older gentlmen in my town here who only put on 53000 miles. my oil pressure comes on almost always during start up and idle which bothers me bc at idle the oil pressure is already low up until 2000 or so rpm i believe. the best way for me to remove the oil pressure warning for me is too simply change out the oil filter which seems to cure the problem for a while actually but then i may get the warning right after i do that. the car runs for maybe a half second with the light on with is roughly the amount of time it takes me to put the car into neutral and kill it lol

im curious to see if the car is actually losing oil pressure or if its just a malfunctioning idoit light im going to be purchasing a mechanical oil pressure gauge from auto meter.

the car runs great i love her lol i only run premium and i occasionally put in a lucas fuel treatment (4.99 at auto zone) with a full tank of gas. i manage to nail 19mpg average

recently put in a new radiator and flushed the coolant, refilled with 50/50 green stuff and a bottle of hyper cool from a company called no rosion i continue to flush coolant every year.

headgaskets are in great shape and the car has never overheated.

oil life is aprox 1 qt every 600 to 1000 miles and im using valvoline conventional 10w30 with a HP2006 K&N oil filter with ever change at 3000 miles (never trusted the oil life sensor)

recently had to replace transmission shift solenoid.

any help would be awesome gents!!

09-25-08, 05:20 PM
My advice:

Replace the oil pressure sending unit first - less than $10 - a lot less than a mechanical gauge. If you still get the low pressure warnings, then remove the sending unit and install the gauge in place of the sending unit. If you still have low pressure, then your pump might be suspect, or the bearings are worn - 600-1,000 miles per quart is high, even for this engine. You may need to do some of the WOTs many recommend to free up sticking rings

09-25-08, 05:31 PM
I would follow Tateo's sound advice. If you do put a mechanical gauge on it, keep in mind that oil pressure at idle is only about 5 psi.

09-26-08, 12:07 AM
thanks for the help gents!

im gonna work on replacing the sending unit before getting into an actual gage

just for kicks what is the normal oil pressure at idle, cruise (2000+rpm), and WOT?

ps im doing more WOT's to help the oil economy thanks for the advice tateos

09-26-08, 09:29 AM
Good post Topic! I've considered putting a mechanical gauge on my Concours also.

It blows me away that there is NO oil pressure gauge in the Concours dash - or even an oil pressure reading accessable with the "info" button. The Concours is suppose to be a sporty version, and you'd think these owners would be more interested in knowing what their oil pressure is. The non-Concours Devilles have a digital reading of the oil pressure under the "info" button. Heck, my Aerostar mini-van has an oil pressure gage right in the dash, and most of the most basic vehicles have them too.

09-26-08, 09:44 AM
The absolute best of all worlds would be to do the install discussed earlier last spring: Plumb in a T fitting at the oil filter adapter sending unit and run a capillary line (with vibration coil) to a mechanical 0 - 80 psi oil pressure gauge in a wood or aluminum panel down on the center console somewhere. Every car and mounting is different....be creative. Understand that in cold weather the gauge will be slow to come up to pressure due to the static oil in the capillary plus the length: it all takes time to warm up to cabin temp. An electric gauge is easier to run wiring to, but most electric oil pressure gauges are no better than an idiot light.

09-26-08, 01:00 PM
Seems to me the idiot light is adequate. The oil pressure is either adequate or not, no? 99.999% of the time nothing is wrong and there is oil pressure and all well in the world. If there isn't enough oil in the pan or if the oil pump fails or an oil cooler line blows or something like that, the light will go on. The light doesn't go on unless there is a problem.

I know some of you guys will disagree, but that's what I think.

I think my wife's car has a much more interesting an useful thing to monitor: transmission oil temperature. That's right - her '04 Grand Prix GTP with CompG package has the trans temp available to display in the info center. Amazing how hot the trans gets here in AZ in the summer - 220s and even 230s are not unusual! I changed the fluid at 30K miles, even though the manual recommends 100K (can't remember if there is a trans fluid life indicator or not)

09-26-08, 01:56 PM
In the 2002 STS a transmission oil temp of 302 degrees sets fans to high. When you consider all the slipping and gripping going on in there it's no wonder the thing runs toasty. There is a transmission oil life indicator, but it never leaves 100% or so unless you overheat the fluid.

I would think a trans oil temp readout would drive you paranoid in hot city driving with the radical temperature swings involved.

An oil pressure idiot light is a go/no go indicator. The real purpose of an oil pressure gauge is long-term comparison. Instantaneous oil pressure means little if you don't have backup history in part of your car-related brain.

As long as transmission fluid is clear red it's OK. Overheated or just plain tired fluid starts to turn amber to brown and smells horrible. I'll wager that a significant percentage of all cars on the road have never had the transmission fluid changed. Not saying that is the smart way to do it......but generally speaking transmission fluid is practically forever unless you race or tow heavy loads.

09-26-08, 05:19 PM
thanks for the help gents!

im gonna work on replacing the sending unit before getting into an actual gage

just for kicks what is the normal oil pressure at idle, cruise (2000+rpm), and WOT?

ps im doing more WOT's to help the oil economy thanks for the advice tateos
Not sure about cruise & WOT, but idle is only about 5 psi as I mentioned in the earlier post. I think the idiot light trips at about 3 if I remember correctly.

09-29-08, 06:48 PM
thanks alot for the info guys

dear submariner409: when u talked about using a T-fitting on the oil filter adapter sending unit where is that exactly? am i looking for a hose or just a wire going to a sensor?

i was flipping through the jegs book i get in the mail once in a while and found there large selection of gauges and found a cylinder head temp. gauge made by Autometer. it has a temp. range of 140-340 degrees.. lol if i remember correctly this idea of head temp was first used on turboprop aircraft engines lol would this gauge be useful for a northstar engine since the headgaskets are very temp. sensitive?

09-29-08, 07:24 PM
Cylinder head temperature gauge thermocouples are usually two types: a washer type which replaces the older style flat spark plug washer, or a dedicated threaded unit which threads into a solid metal area near the exhaust valve/port. Not practical on a Northstar, and not useful, either. Don't forget that the cylinder head metal in a water cooled engine is subject to a huge range of temperature differences depending on proximity to the coolant passages, so what do you want to monitor ?? An air cooled cylinder head has less of a temperature difference. Liquid cooled aircraft engines (Allison, Rolls Royce) use exhaust pyrometers to monitor exhaust gas temperature and changes to fuel mixture, among other sensors......

The T fitting referred to is a pipe T: the existing oil pressure sending unit goes in one leg, an electric gauge sending unit or mechanical gauge capillary connection goes in the other, and the third leg is fitted with a short pipe nipple which threads into the original hole in the oil filter adapter unit, thus allowing the same (original) oil pressure tap to feed 2 sending units.

09-30-08, 12:45 AM
ah very interesting thanks for the info man i just picked up a brass t fitting at the auto parts store and im gonna be sending in for the gauge really soon thanks for expert advice gents always a pleasure!