Oil pressure testing and startup from long period standing

[TimJM]

I will be testing my oil pressure gauge soon and want to check my plan is the best/safest way. Also, this would be useful information for me when my TVR(s) have been in storage/repair and haven't been started for a while.

To get the pressure up I was planning on removing the fuel pump relay (#4 I think) and cranking the engine over. But, somebody said I should remove the spark plugs also - is this the best way?

Plus, would pulling out fuse 19 (fuel pump and lambda heaters) have the same effect as pulling out the relay or would that confuse the ECU?

Or should I leave the spark plugs and fuse/relays alone and just remove the fuel pump power? That sounds easier but I am looking for advice on the safest method.

Thanks,

[Mags]

I expect a more comprehensive answer will come along but you pull the spark plugs as without these the pistons do not have to compress air which places considerable load on the engine, the air just gets pushed out the plug hole. You will notice the engine spins over much faster with all the spark plugs removed as there is much much less resistance.
It's common practice to do this to build up oil pressure after a rebuild, long layup etc.

[a1rak]

You have to be careful if the engine has been standing for a very long time or rebuilt. Sometimes the pump on the V8 will not prime itself even with the plugs out as the starter just does not spin fast enough to lift the oil and you can do more damage with the extended spinning time not priming.

When I rebuilt my engine I primed the pump and filled the main gallery from underneath the car using a external hand pump via the oil filter gallery. Either that or just start it if its not been standing to long as the bearing housings will always hold a residual of oil easy enough for a restart, the faster revs will immediately pick up oil on anything other than a bone dry pump.

[ridds]

You can faff around taking plugs out, removing fuel pump fuses etc but most of the time you will end up making more trouble for yourself.

If you were really fussed about priming then pop the oil filter inlet hose off, lift it up and pour oil in VERY slowly holding the pipe with a rag. You will spill the oil! Allow this to drain back to the pump, repeat 2-3 times. Refit the hose and then just start it up briefly.

Cranking usually mean taking longer to build pressure due to the slow speed of the pump. When priming engines I start them and shut them down as soon as they fire. This helps pump the oil against any airlocks and reduces the heat build up in bearings.

[Tanguero]

a1rak said:

You have to be careful if the engine has been standing for a very long time or rebuilt. Sometimes the pump on the V8 will not prime itself even with the plugs out as the starter just does not spin fast enough to lift the oil and you can do more damage with the extended spinning time not priming.

When I rebuilt my engine I primed the pump and filled the main gallery from underneath the car using a external hand pump via the oil filter gallery. Either that or just start it if its not been standing to long as the bearing housings will always hold a residual of oil easy enough for a restart, the faster revs will immediately pick up oil on anything other than a bone dry pump.

^^^^
This

You will not spin it fast enough on the starter to prime the pump and run a risk of damage by turning it on dry bearings.

[TimJM]

Thanks for this advice. So the general consensus is to just start her up and see what happens.

I will only be running the engine for a few minutes (if that) to check the oil pressure. I know the gauge isn't reading since speedy cables repaired the water temp part not reading (that now works) and just wanted to confirm with a pressure gauge attached to the block that the pressure was there before removing the gauge and sending back to speedy cables.

The oil warning light doesn't come on (so assuming worst case at least 7-10psi) and the last owner who sent the gauge to speedy cable originally said it was working fine (around 50psi) before he sent the gauge away to have the water temp part fixed. When it was refitted the water temp works and the oil pressure stopped working.

[Tanguero]

When I started mine after I had my engine out and completely drained, I agonised for days about priming oil pumps and eventually talked to Dan Taylor who advised to simply fill the engine right up to the top with oil (and then a little more to be sure) and start it up and hold it at 2k rpm while watching the pressure gauge carefully and kill it if there is no pressure withing 30 seconds. I followed his advice and sure enough the pump self primed and I had full pressure within 10 seconds.

[ukkid35]

Tanguero said:

I followed his advice and sure enough the pump self primed and I had full pressure within 10 seconds.

I killed mine after about 5 seconds with no pressure showing, tried again after checking levels and had pressure within 2 or 3 seconds.

[Supateg]

2k is a low load speed for most engines.
When I do cam work on a engine after I start it up I hold the revs at 2k unlit I have satisfied the whole lot is well lubricated. Usually two minutes to bed in again.

[TimJM]

OK - I will order an oil pressure gauge and connect it up to the block. So if I start the engine as is and no pressure after say 15 seconds then kill it.

I expect it will be OK but knowing little about cars I don't want to risk damaging it.

[TimJM]

Another question while I wait for someone to help identify the correct thread for the oil pressure hose in from the pics I posted in general TVR stuff...

I managed to undo the oil pressure feed hose (it was bloody tight) expecting oil to spill out but there wasn't any spillage. The pipe into the wing that feeds the gauge has oil reside around the top and down in the pipe as can be seen in the pic below but it isn't full of oil.



Also, the braided hose that feeds this pipe that runs back to the block also has oil residue but again it isn't dripping.

My question is as this measures pressure should the pipe (and if possible the tube) be topped up with oil to remove the air or doesn't this matter? Obviously the air will compress easily where as the oil won't - will this affect the reading?

The previous owner said the oil pressure gauge was working until it was removed and sent to speedy cables to repair the water temp part. I haven't started the car up yet but I did when I purchased it and the water temp was working but not the oil pressure gauge. The oil warning light wasn't on and the previous owner said the oil pressure gauge hasn't worked since it came back from speedy cables.

I am wondering if the previous owner fitted the gauge back in themselves and perhaps it isn't fitted correctly or should be topped up with oil not full of air?

Of course I know nothing about this in reality so could be barking up the wrong tree. If I'm talking bks and air in the oil pressure hose/pipe doesn't matter please let me know.

I suppose if I get a test gauge and connect it up to the engine that will tell me what's going on...

[TimJM]

Thinking about this some more, would air in the capillary pipe/hose matter?

Would the oil just compress the air to the same psi? If I put 80psi of oil behind air won't the air compress down to 80psi too?

[ellum]

Air can be compressed, fluids not.

Elvis

[TimJM]

ellum said:

Air can be compressed, fluids not.

Elvis

Air can relatively easily, fluids not very easily. We consider fluids incompressible because they compress only a very small amount in typical applications.

Anyhow, just because air compresses would this stop my oil gauge reading?

My thinking last night (after a scotch to help lubricate the thought process) is if I have a tube full of air and then pump in oil with 80psi of pressure then yes, the air will take up far less room in the tube but it should stabilize at 80psi too. Pressure is pressure regardless of the air/gas/fluid compressed.

Although I guess air in the tube isn't a good thing and would make any reading less responsive. Or I could be wrong completely.