Check Oil Pressure After Rebuild

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garrycol
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Check Oil Pressure After Rebuild

Post by garrycol »

My 4.6 has been built and is in the vehicle - prior to actual start I want to make sure I have oil pressure. So today I filled it with oil and started cranking the engine in short bursts - while cranking the oil pressure went out - great I thought but then I remembered that while cranking, power is actually diverted away from instruments etc. I removed the the lead from the oil pressure switch and earthed it - yep oil pressure light on ignition on but off when cranking with no oil pressure switch in the circuit.

So how do I conform that I actually have oil pressure before I fire up the engine - I have a gauge as well but I know from experience, that on cranking it does not develop enough pressure to register on the gauge until the engine fires up.

Thanks

Garry



DaveEFI
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Post by DaveEFI »

I'd never seen an oil pressure switch wired so it doesn't work when cranking. Makes no sense to me why anyone would design it like that. Only reason to kill accessories when cranking is to reduce current consumption - and instruments take so little it's not worth it. They are usually on the same circuit as the actual ignition, as regards the switching.

However, if you're not sure about your wiring, use a DVM to show the pressure switch opening.
Dave
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garrycol
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Post by garrycol »

I am sure of the wiring as it has not been touched - What is a DVM?

unstable load
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Post by unstable load »

Digital Volt Meter.
Pull the terminals on the switch and set the meter to beep when the terminals are touched together. Connect it to the terminals and crank the engine. If you have pressure it will make the switch and the meter will tell you.
Cheers,
John

garrycol
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Post by garrycol »

Ok - thanks is obvious :)

Also thinking about this more I was going to get a separate power supply with a light in circuit and crank until the light goes off - basically the same as the DVM process.

Ok - just connected up a separate power supply - the light stayed on even after 30 secs of cranking - so it looks like either the switch is faulty or it is not getting oil pressure. Not prepared to crank any further as the engine is only being lubricated by the assembly lube.

The engine is a 4.6 so supposedly the oil pump does not need priming though I did fill it with petroleum jelly but the engine has been turned over many times as part of the assembly/set up process.

I guess I need to pull out the switch etc and check whether they are working.

Cheers

Garry

DEVONMAN
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Post by DEVONMAN »

Pull out the switch and turn the engine over with a rag over the hole. If oil pours out then all is usually ok with oil flow.
1950 A40 Devon Hotrod with 5.0 twin turbo RV8.
EDIS8 wasted spark, Holley Injection.
Been as far as the Moon and back in 57 years of driving. Same Car, 5 engine upgrades !!!


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garrycol
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Post by garrycol »

Been playing with this all day - when I put this together I wanted both a pressure light and oil pressure gauge and due to space constraints I used the top port on the oil filter housing for the pressure light switch and the lower port for the pressure gauge sender.

So to get the switch out the lower radiator hose has to come out - thankfully no coolant in there.

And of course due to the tight spot I managed to damage the thread on the top port - to fix it properly the timing cover needs to come off but that isn't going to happen - thankfully the oil system only runs to a max of 45psi so good remaining threads will be strong enough to hold the screw in plug I put back in.

So with both ports clear I tried to put oil into the lower port so that the oil will flow down to the pump. The oil just dribbled out so not much use. I then cranked the engine as suggested and oil flowed out so it would seem that the oil was at least in the oil pump and filled up to the oil filter.

I put the switch back in a rigged up an indicator light and cranked away and nothing happened for another 30 secs and then the light went out.

So a whole day wasted - caused some damage - but the engine just needed a couple of minutes cranking to get oil pressure.

However I also look at it this way, what if I had not worried about getting oil pressure at this stage and just fired it up and there was an issue with oil pressure then maybe a new engine would be history.

Thanks for the input - it helped a lot.

Garry

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