Oil gauge flicker

[MrTibbs]

Hi folks,

My oil gauge always has this kind of flicker or wobble, and I seem to remember reading this can indicate bad rod bearings.

Since I'm going to be driving the car 3k miles across Europe and back this summer I want to make sure it all checks out OK. Compression test indicates compression's fine and there's a couple of small ticks from the engine but I'm fairly sure it's just injectors clicking.

Anyway, I've put a (not very exciting) video clip on youtube
YouTube - ‪Porsche 944 oil gauge flicker‬‏

Does this look like rod bearings, or just a dodgy gauge? My coolant temp gauge also jumps up and down quite a bit (it's worse when the lights are on - going to do the relay upgrade this week hopefully). When I replace my dash with my spare one I'll run another ground harness for all the gauges I think. Also plan to put an extra ground from the intake to the chassis ground point.

I've cleaned the grounds under the dash, but the main engine ground is hard enough to get to that I'm leaving it at the moment until I take the intake off (which I'm planning to do shortly). The connections at the sender are also covered in oil and gunge - I cleaned one off, sanded the conection clean and protected it with dielectric grease, but the other one's harder to get to and as it was getting dark I didn't get round to finishing it off.

I think I'm answering my own question here (it's the grounds, man up and clean them), but can someone reassure me that's the case.

Mike

[Guest765]

Originally Posted by MrTibbs

Hi folks,

My oil gauge always has this kind of flicker or wobble, and I seem to remember reading this can indicate bad rod bearings.

Since I'm going to be driving the car 3k miles across Europe and back this summer I want to make sure it all checks out OK. Compression test indicates compression's fine and there's a couple of small ticks from the engine but I'm fairly sure it's just injectors clicking.

Anyway, I've put a (not very exciting) video clip on youtube
YouTube - ‪Porsche 944 oil gauge flicker‬‏

Does this look like rod bearings, or just a dodgy gauge? My coolant temp gauge also jumps up and down quite a bit (it's worse when the lights are on - going to do the relay upgrade this week hopefully). When I replace my dash with my spare one I'll run another ground harness for all the gauges I think. Also plan to put an extra ground from the intake to the chassis ground point.

I've cleaned the grounds under the dash, but the main engine ground is hard enough to get to that I'm leaving it at the moment until I take the intake off (which I'm planning to do shortly). The connections at the sender are also covered in oil and gunge - I cleaned one off, sanded the conection clean and protected it with dielectric grease, but the other one's harder to get to and as it was getting dark I didn't get round to finishing it off.

I think I'm answering my own question here (it's the grounds, man up and clean them), but can someone reassure me that's the case.

Mike

likely the grounds. my car for some reason has started dropping .5 bar under load. what i mean by that is, coasting in 5th gear at speed and then getting on the throttle, it drops from 5 bar to 4.5, or from 4.5 to 4, etc. i would trade you? rofl.

[John_AZ]

I replaced the oil pressure sender on the oil cooler housing and the "jumpy" dash needle was gone.

Make sure the wires from the oil pressure sender are not cracked. They go over the waterpump to the top of the engine. This gets hot and gets the sheilding brittle.

Do not over tighten the oil pressure sender connections. They are hollow and very brittle.
Would be a shame to buy another if heavy handed.

GL

John

[Guest765]

Originally Posted by John_AZ

I replaced the oil pressure sender on the oil cooler housing and the "jumpy" dash needle was gone.

Make sure the wires from the oil pressure sender are not cracked. They go over the waterpump to the top of the engine. This gets hot and gets the sheilding brittle.

Do not over tighten the oil pressure sender connections. They are hollow and very brittle.
Would be a shame to buy another if heavy handed.

GL

John

john is correct and his post did bring to mind, the oil pressure sender wires are THIN so i could see them becoming damaged easily.

[MrTibbs]

Thanks. At least no-one thinks it's rod bearings (car has around 130K on it and seems OK, but drivetrain's a bit trashed so think it might have had a couple of hard owners).

I'll clean the connections and test the condition of the wires when I get a chance. it only really flickers at idle anyway - under load it stays stable.

Mike

[Guest765]

Originally Posted by MrTibbs

Thanks. At least no-one thinks it's rod bearings (car has around 130K on it and seems OK, but drivetrain's a bit trashed so think it might have had a couple of hard owners).

I'll clean the connections and test the condition of the wires when I get a chance. it only really flickers at idle anyway - under load it stays stable.

Mike

i was told rod bearings is when your pressure can't get above ~2bar? or is that the crank bearings?

[HondaDustR]

Originally Posted by fwayfarer

i was told rod bearings is when your pressure can't get above ~2bar? or is that the crank bearings?

Bad main or rod bearings could cause oil pressure to drop. Think of the oiling system as like one of those garden sprinklers with the curved tube with holes in it, where the holes are the restriction of the small bearing clearances. If you drill one hole much bigger, like when one bearing goes bad and runs large clearances, the pressure will drop since more liquid escapes out that hole, and it doesn't really matter which hole you drill to cause the problem. Hydrodynamic bearings do not require feed pressure to operate but they do require a constant supply of fluid to prevent running dry and to provide cooling. High enough system pressure is simply to ensure all of the bearings get sufficient flow, alot like how the sprinkler will not spray evenly across all of the holes below a certain feed pressure. I think the rule of thumb is at least 10 psi per 1000 rpm, and the factory spec is 4.5 bar at 5000 rpm.

The 944 almost never eats main bearings. It's usually rod bearings, and usually the #2.

My gage jitters and also dips under load. I have a dedicated ground and supply to the gage and it didn't fix the problem. It probably is just the sender, but the wires are also worth a look.

[MrTibbs]

Thanks Honda,
I'll try cleaning and possibly re-wiring it at some point. If that doesn't work I'll see if the sender on my spare engine's any better.

Mike

[Guest765]

Originally Posted by HondaDustR

Bad main or rod bearings could cause oil pressure to drop. Think of the oiling system as like one of those garden sprinklers with the curved tube with holes in it, where the holes are the restriction of the small bearing clearances. If you drill one hole much bigger, like when one bearing goes bad and runs large clearances, the pressure will drop since more liquid escapes out that hole, and it doesn't really matter which hole you drill to cause the problem. Hydrodynamic bearings do not require feed pressure to operate but they do require a constant supply of fluid to prevent running dry and to provide cooling. High enough system pressure is simply to ensure all of the bearings get sufficient flow, alot like how the sprinkler will not spray evenly across all of the holes below a certain feed pressure. I think the rule of thumb is at least 10 psi per 1000 rpm, and the factory spec is 4.5 bar at 5000 rpm.

The 944 almost never eats main bearings. It's usually rod bearings, and usually the #2.

My gage jitters and also dips under load. I have a dedicated ground and supply to the gage and it didn't fix the problem. It probably is just the sender, but the wires are also worth a look.

great explanation, thanks for this.