Oil pressure gauge slow to respond

[Tom W]

Hi everyone,

The oil pressure gauge on my 2200tc is very slow to respond when the car's been standing for a while. We're talking standing for a week, and literally taking minutes to move. When it does move, it goes up to above 50psi at idle, and half way between 50 and 100 at speed. The light goes off a few seconds after starting the car from cold, and instantly when started from warm. It's only started doing this recently. I've started putting a lot more long distance mileson the car at motorway speeds in the last month, but for the last few years, it's not really had much hard use. It doesn't sound rattly and there's no notable change when the gauge finally wakes up. Once everything's woken up, turning the ignition back on immediately after stopping the car shows the light takes a while to come back on and the gauge to drop to zero, so there's definitely residual oil pressure.

So, my thoughts are as follows:

1. I maybe have the wrong filter on without the internal flap valve and standpipe. I've just swapped the filter for another that I had so I'll see if this makes a difference, but I don't know that the new filter has the correct internals. I'll have to let it stand a few days before I can check this. Interestingly, starting the engine after fitting the new and therefore empty filter had the light go out and the gauge come up almost straight away.

2. The sender has a dodgy connection that requires the engine to reach a certain temperature before it makes contact.

3. The sender's failing internally giving the same result as the thought above.

4. The gauge is accurate and there really is no pressure in the main oil gallery. The light takes it's pressure feed from the pump housing and the gauge measures pressure where the fat oil feed pipe enters the side of the block, so it's conceivable there could be 2 pressures within the engine. The timing chain tensioner feeds directly from the pump, so that would explain the lack of rattle. Maybe the large feed pipe has collapsed internally?

5. Maybe there's something up with the oil pressure relief valve? I don't know where this is located and where the gauge and light measure relative to it, but could this be sticking open and giving the symptoms I describe?

I can't see my engine lasting long if this really is a mechanical problem. Maybe a V8 would be better suited to long distance commuting.

Cheers,

Tom

 

[Tom W]

Researching generic oil systems further, I wonder if the filter I had on was one without an internal relief valve?

My theory is starting the engine from cold would see the light on for a couple of seconds until the filter filled and the pump body pressure built. The cold oil would be too thick to flow through the filter, effectively building up pressure behind the filter element and recirculating through the pressure relief valve. Eventually, as the oil warms it's able to flow through the filter and enter the oil galley, where pressure is shown on the gauge. If this is the case, then This won't have been great for the long term condition of my engine. Still, live and learn. I'm supposed to enjoy fixing old cars anyway.

I'll have to look at the filter I took off to see if that has a bypass, but I won't be back to the car for a few days to check. The one I've just fitted does.

 

[Demetris]

Based on experience from my own car (capillary oil pressure gauge that is plumbed directly in the block oil gallery) as soon as the oil warning light goes out, the needle in the gauge starts to register. If there is a delay in building up the oil pressure for any reason (empty / wrong oil filter etc) then this shows both in the warning light and the gauge and on top of that the engine noise is different (slight bottom end knock). Probably it is the sender unit of your gauge that starts playing up.
If you could plumb in a master gauge or a capillary unit, you would confirm that.

 

[j_radcliffe]

Install a mechanical pressure gauge and see what number you get from that. You should be able to do this on a temporary basis, with the pickup feed on the rear right hand side of the block, and compare.

Here some some instructions in the link below. Unless you want to have a gauge inside the dash, can just have a pressure gauge in the engine bay, start it up and observe what it does, and compare to the one inside the car.

viewtopic.php?f=2&t=7044&hilit=+oil+gauge&start=0

Check wiring to the electric gauge. I would also remove and inspect the sender, and clean it with de-greaser. There could be an internal blockage that is impeding the flow of oil pressure to it.

James.

 

[Tom W]

I used the car again at the weekend and I'm 99% certain the problem is electrical not mechanical. Start the car and the light goes out after a couple of seconds, but no life from the gauge. The gauge remains dead for about 10 miles this time. When it eventually registers at 70mph, it shows 75psi, same as always. Hot idle shows 55psi, again normal. There's no change in engine noise between the gauge not registering and registering and there's no more noise from the engine that wasn't there before. If I did really have no oil pressure, then I expect things would be really broken by now.

There are two anomalies that make me think the problem might be slightly more than a dud sender unit. First, a couple of times after starting the car from cold, the oil light went out, then came on a few seconds later, bright not flickering. There was no reading on the gauge. Both times I immediately stopped the engine. On restarting, the light stayed off. Secondly, when I opened the driver's door, the fuel gauge flicked round. The ignition was off when this happened. I don't have my wiring diagram with me to check, but wonder if there's a way the interior light could earth through the gauges.

I'll work through this methodically and let you know how I get on.

Tom