Mechanical oil pressure gauge problem

[JXL 12]

This spring when I first started my car the oil pressure gauge went all the way around 360 degrees and is sitting against the pin. I assumed that the gauge screwed up and went and bought another one, put it in, and it did the same thing. Anyone have any idea what is causing the issue? Car is a '69 coupe with a 351w. The gauges worked fine all last summer but now I am having this issue.

[Ridge Runner 1,113]

What is the max reading on the gauge ? My 351 will hit 100 on the gauge when the motor is cold ,drops to around 65 or 70 when hot .

[Kyle T 19]

When you short the wire at the oil sending unit to ground the gauge pegs out like that.  It's one way to test to see if your gauge is working.  If your sending unit is shorting out it will have the same effect.  You could also have a short in the wire somewhere along the line.  At any rate it is going to ground.

 

Kyle T

[sportsroof69 13]

He said it's mechanical, so no grounding required.

[1969_Mach1 333]

Could very well be a gauge issue.  If not, the pressure relief valve in the oil pump might be stuck?  I haven't verified, but most stock or high volume pumps seem to release in the 65 psi range.  High pressure pumps can cause a host of issues and are typically frowned on and not recommended by builders. 

[Ridge Runner 1,113]

Never had a problem with high pressure pumps except for the gauges ,plastic oil lines will blow off or break .usually the gauge is not high enough to work .I would try another gauge .

[Rsmach1 71]

The problem with high oil pressure in street engines is bearing wash and bearing erosion, drastically reducing bearing life.

[1969_Mach1 333]

The problem with high oil pressure in street engines is bearing wash and bearing erosion, drastically reducing bearing life.

 

Thank you.  Last time I mentioned that it seemed people thought I was making it up.

[sportsroof69 13]

Never use the plastic line that those gauges come with. Always run a good solid copper line.

[Rsmach1 71]

Thank you. Last time I mentioned that it seemed people thought I was making it up.

Nope it's a fact and I've seen and experienced it, too high pressure at the bearings doesn't allow a proper film across the bearings surface, and can actually wear grooves in the bearings over time.

 

Edit; and you are welcome 1969_Mach1

[JXL 12]

The weird thing is last fall the gauge was fine. I had not started it in a few months because I was replacing the front seal and the intake manifold gasket. Then once I started it up I had the issue with the gauge.

[JXL 12]

I should have mentioned too that it is a melling high volume pump but regular pressure. Would sit at 20 psi at idle when warm last year. The gauge goes to 100 psi so I can't see it running that high. When the gauge was working it would go to 60 psi when cold.

[Rsmach1 71]

X2 the pressure relief valve in the oil pump is most likely stuck.

[JXL 12]

_{Thanks for all the feedback. My next day off from work I am going to drop the pan and remove the pump. Is there a way I can fix it or is it more advisable to simply change out the entire pump to a new unit?}

[1969_Mach1 333]

I would replace it unless you find something in there binding up the pressure relief valve.  I might even think about installing a standard volume pump like one of Mellings heavy duty standard volume pumps, http://www.summitracing.com/parts/mel-10832/overview/make/ford .  But a lot of that depends on how your drive the car and the bearing oil clearances. 

[JXL 12]

That was going to be my next question, standard or high volume. The engine is a 351w, .030 overbore, stock crank and rods, keith black pistons, 10.5:1 compression, lunati cam and AFR 185 heads. It is an automatic car so it only sees 5500 rpm and not very often as I drive it fairly easy. I have the MSD 6AL box rev limiter set at 6000 RPM. I am thinking that a standard volume would be ok but I was looking for some advice.

[Rsmach1 71]

Oil pumps aren't all that expensive, I would definitely vote to replace it. As far as standard vs high volume, as 1969_Mach1 stated it would be helpful to know what the bearing clearances were when built. Any idea? Did your engine builder recommend the hv pump? How many miles are on it?

[JXL 12]

I believe the clearances are the standard .002" of an inch or so. The builder put in a melling high volume pump so maybe I will just replace it with the same one.

[1969_Mach1 333]

If that's what the builder installed he may have had his reasons for doing so.  It's probably safe reinstall the same type.  Rsmach1 seems to be more knowledgeable in this area.  Lets see if he chimes in with some information.

 

The bearing clearances on my 351W motor are on the small side of the OEM range so I use this Melling standard volume pump http://www.summitracing.com/parts/mel-10832/overview/make/ford .  I tried a Melling high volume pump once in this motor.  I didn't have any issues.  But it was extremely hard to turn as I discovered when priming the oil with a drill motor.  I wondered if there would be excessive wear on the gears that drive the distributor so I went back to a stock volume pump.

[Rsmach1 71]

If that is what the builder installed I would use the high volume pump, and after re-reading you having 20psi at idle hot the hv would be a wise choice. I would highly recommend you pick up a new pump, and not mess around with the old one. Also since there was enough pressure to peg the gauge, it would be a good idea to check the distributor gear just to be safe.

[JXL 12]

OK guys thanks for all the help. I am going to order up a new high volume pump and install. I will let you know how I make out.

[JXL 12]

So I ordered up a new Melling HV pump installed it and it works great. Sits at about 50-60 psi while cruising and about 30 psi at idle when warm. The old pump looks like a Motorcraft unit as it has a ford part number stamped on it and a big "M". The new Melling pump looks like much better quality as it is cast iron/steel and the old unit is cast aluminum. I tore the old one apart and the relief valve was seized solid. I could move it with a hammer and punch but just barely. I will be giving the guy that did my short block for me a call as he said that he put in a Melling pump and it definatly was not. Thanks again everyone for pointing me in the right direction.

[1969_Mach1 333]

Nice work.  Yeah, every original Ford oil pump I have seen has an aluminum housing.  Which would definitely be a stock volume oil pump.

[Rsmach1 71]

You're welcome, glad you got it worked out.