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This is in an 86 951 engine with new rod bearings, rebuilt top end and turbo. Engine installed in 87 924s chassis. I finally got to crank the engine for the first time today.
I cranked it about 5 times today for about 10 seconds each to build oil pressure. Coil unplugged; fuel tank empty. Using the stock electric 924S oil pressure gauge, it never registered anything. I'm wondering if the gauge is even getting a signal (it worked before I swapped the engine out). On the electric oil pressure sender, I checked the wiring and even swapped the poles to see if it would peg the gauge at 5, but again the gauge didn't register anything - this is with the ignition at position 2.
So now I'm concerned that I'm either not building oil pressure, or the sender is bad, or the gauge is bad.
Any suggestion for what to do next? Install a new oil pressure sender?
and yes, it has 6.5 quarts of driven BR30 break in oil in the sump
Try using a direct reading gauge. You'll have to make an adapter to get past the oil pressure sender threads..and into the new gauge and plastic line. This type of gauge assembly can usually be picked up at your local FLAPS for under 20.00 or so. The pressure sender threads & adapter may be the tricky part..HTH
This is in an 86 951 engine with new rod bearings, rebuilt top end and turbo. Engine installed in 87 924s chassis. I finally got to crank the engine for the first time today.
I cranked it about 5 times today for about 10 seconds each to build oil pressure. Coil unplugged; fuel tank empty. Using the stock electric 924S oil pressure gauge, it never registered anything. I'm wondering if the gauge is even getting a signal (it worked before I swapped the engine out). On the electric oil pressure sender, I checked the wiring and even swapped the poles to see if it would peg the gauge at 5, but again the gauge didn't register anything - this is with the ignition at position 2.
So now I'm concerned that I'm either not building oil pressure, or the sender is bad, or the gauge is bad.
Any suggestion for what to do next? Install a new oil pressure sender?
and yes, it has 6.5 quarts of driven BR30 break in oil in the sump
The engine oil pump is not a positive displacement pump, so it cannot pump air and create a vacuum to lift the from the sump to pump cavity. This means the oil pump is not primed. To prime the pump, follows below.
Pressurize the oil sump with a controlled compressed air, 10-15 psig, by inserting air gun with seal into the dipstick holder tube. Block off, seal the AOS hose so air cannot escape. Have a 2nd person crank the engine. Oil pressure should build.
Hey Joseph, what are you doing over here on the 944 forum? Two of the best have already responded. That said, I will quibble with them cause that's what we do on forums The quickest, simplest test for oil pressue is to remove your oil filter and crank the engine on the starter (plugs out helps). If everything is working, you will get oil out of the side port in the filter housing. Either use a remote starter switch or have a friend crank the car while you watch. It will make a small mess but it is a good mess, if you know what I mean. I will quibble with Tom in that the oil pump is much closer to a positive displacement pump than it is to a centrifigral pump but I will agree sucking air is not its strong point. If the pressure on the dipstick method works for you, then problem solved, hopefully. That said, I just particpated in a full bottom end rebuild of a 944 NA a few weeks ago and we got oil coming out of the filter without any help from air pressure, ect. So try the air pressure method with the filter off and get back with us.
Article about the oil pump: https://newhillgarage.com/2018/01/12...ump-explained/
Article about the entire oiling system: https://newhillgarage.com/2013/06/25...tem-explained/
Hey Joseph, what are you doing over here on the 944 forum?
LOL this forum is where I started out 20 years ago.
Thanks for the help guys. I'll try the pressurized crankcase approach.
Also it's possible the oil pressure gauge is not receiving a signal from the sender, but using this diagram the wiring should match up from the 951 engine harness to the 924 chassis harness. (#6 pin)
But wouldn't the gauge peg at 5 if the sender poles were reversed and power applied?
Last edited by joseph mitro; 08-23-2021 at 02:47 PM.
For what it's worth... I had the same issue with a similar engine (new rod bearings, rebuilt head, etc.) It took at least that many tries of at least that long (and I want to say longer) to see anything. Did you take out your plugs? If not... give that a try. Turns over much faster that way...
This is an aside, but related:
When rebuilding a 944 engine I always disassemble the oil pump to inspect the housing and gears. When reassembling, coat the gears and housing with white grease (it doesn't take much). The grease closes up the clearances and maximizes the 'suck' to pull oil up the pickup tube. The result is oil pressure without the mess or headache when there is none.
MM
PS: You'll need a hand held hammer type impact driver to disassemble the pump (cheap) and 574 to reseal the pump housing. You'll see where the factory sealed it, so just duplicate what they did.
Turns out the oil pressure gauge wasn't even hooked up correctly. So once I wired it correctly and pressurized the crankcase, I got a slow build up to 5 bar of pressure.
Woot!
No strange noises either so far. Next up is fixing whatever coolant leaks I have and then filling the gas tank then hopefully the car will start up
08-22-2021, 11:48 PM
troubleshooting no oil pressure on rebuild
The quickest, simplest test for oil pressue is to remove your oil filter and crank the engine on the starter (plugs out helps). If everything is working, you will get oil out of the side port in the filter housing. Either use a remote starter switch or have a friend crank the car while you watch. It will make a small mess but it is a good mess, if you know what I mean. I will quibble with Tom in that the oil pump is much closer to a positive displacement pump than it is to a centrifigral pump but I will agree sucking air is not its strong point. If the pressure on the dipstick method works for you, then problem solved, hopefully. That said, I just particpated in a full bottom end rebuild of a 944 NA a few weeks ago and we got oil coming out of the filter without any help from air pressure, ect. So try the air pressure method with the filter off and get back with us.
