Startup after rebuild - oil pressure off the dial...

[limey66]

So, I got my baby started at the weekend, it's the first time I've ever heard her - brought a tear to my eye.

Anyway, apart from a couple of setbacks, like a leaking fuel pump, the problem that concerns me is the oil pressure is off the gauge. Any ideas what might cause this?

The sender is new, the car is totally rewired, the engine has been sat for at least four years after a rebuild (I re-did the top end for unleaded).

If, as I fear, it's the oil pressure relief valve how do I get to it? Sump off?

If the sender wasn't earthed properly (I used PTFE tape, not the conductive sealer, but I think it made connection) would that make it go off the top of the scale?

Thanks in advance Stangnetters.

 

[dennis112]

You may have an electrical problem. Poor earth (grounding) is not going to max out a gauge, although putting the sensor wire directly to ground will.

Since everything is new, you should first get a mechanical oil pressure gauge (kind with the little tube) and recheck your oil pressure. You really need "the second opinion" before diving into the engine again.

Pressure relief is in the oil pump. There is also one in the oil filter, so you could easily replace the filter.

Questions to ask AFTER you recheck the oil pressure with a mechanical gauge: Did you use a high volume unit? Do you measure (and remember) the actual bearing clearances? Did the pressure drop after the engine warms up?

Spend the money on the mechanical gauge, even if you use it temporarily just for troubleshooting this problem.

 

[Timmy]

Does the gauge move when you just turn the key on? If it maxes out when just the key is on, it's a grounding issue for sure.

Tim

 

[limey66]

Poop - I'll spend the money on a mechanical gauge. I suspect the pressure relief valve has stuck after being left for so long. If I need to get to the valve, where is it, can I just drop the sump?

 

[spirockp]

So does that mean you tried an dhooked up the mechanical gauge?

 

[limey66]

So does that mean you tried an dhooked up the mechanical gauge?

Not yet, I need to see if our crappy auto shops over here have anything suitable. I can buy stickers, LEDs, spotlamps, big bore bolt-on exhausts, and anything that morons want to put on their mum's shopping rocket, but proper car stuff...nada.

I'll try an engineer's factors not far from where I work - any idea what thread I'm after?

 

[HistoricMustang]

This is exactly why I use mechanical on all gauges except the voltmeter.

HistoricMustang
www.historicmustang.com

 

[shotsy]

On a freshly rebuilt motor isnt the oil preasure going to be high until it's broken in properly. On my C I'm munning at 70 psi on the mech gauge and the gauge in the dash is pegged, all I have done to break it in is the cam breakin and beat it around the block a few times, I expect to see the preasure drop some as thing start to break in further, Dunno if I'd be to worried about high oil preasure on a fresh motor.

 

[limey66]

So what oil pressure am I looking for in a new engine then?

 

[Tim65GT]

Is your gauge off scale before you crank it up? Or is it sensing oil pressure when you start it, then it pegs? Determine if it's an electrical problem first. Check (with the engine running) with a voltmeter at the sender body to ground. If you get zero then your ground is ok, you don't have to worry about the PTFE tape insulating it. If you get more than a volt or so, the the tape is in fact insulating somewhat and you'll have to remove the tape and just put in in without it.

My new VDO oil gauge pegs when started cold. And from your video it looks damn cold. The oil is thicker and will give a much higher reading. Let it get to operating temperature and see what you get at idle.

Congrats on getting it fired up! it sounds great.

 

[shotsy]

My first start was about 80 psi and then after the cam break in it dropped to about 70 psi. Now when it's fully warmed up at idle I'm around 50-60

 

[limey66]

All good advice guys, thanks. I'll check this weekend.