Oil lines and oil pressure loss???

fastfredracing · 05-21-2005, 09:50 AM

Just wanted to see what you guys think??. Is it possible for a cruched front oil cooler line to cause a lower oil pressure reading??. My motor is relatively fresh, and has perfect oil pressure when cold, and all the way up to 180c ( 1 bar at idle, 4 bar at 5000, but at 190c, my oil presure will peak at only 3.5 bar, but is still almost 1 bar at idle. When watching my gauge it seems that I loose about 1 bar almost immediately right about the time the temp sees 190c on the guage, and I have also watched the oil guage while feeling the oil lines and it seems that the presure loss happens as the front oil lines are begging to get warm. I would say that the lower line is nearly 60% restricted at the worst point, but has at least 5 large dents in it. Any input on this would be greatly appreciated..

350HP930 · 05-21-2005, 11:16 AM

Keep in mind that as your sender gets old and worn out its accuracy may also be varying as it gets hot.

cgarr · cgarr's Garage

Doesn't all oil return to the tank after its cooled then taken from the tank direct to the pressure side of the pump? (that big S hose) If so, if your line was blocked then your oil tank would be running out of oil? My thinking could all be wrong on how it works? in that case, never mind

Craig

fastfredracing · 05-21-2005, 08:17 PM

I had actually replaced the sender when I built the motor, but I also swapped it out with the old one later and got the exact same result, I also connected a mechanical pressure guage , and it verified the same thing, and I believe that you are right that the oil feeds from the cooler back to the tank and then into the pump. I think I may have repaired this today, only I don't know what fixed it. I attempted to reshape the brass line a little bit with some channel locks (crude but effective), and I also removed the oil pressure spring and valve, cleaned them and shimmed the oil pressure spring. Just went out for a 70 mile drive, so far all is ok. After some back road thrashing , oil temps at about 200, 5 bar at 4000, whew!! Thanks for reply. I am new to this site, It rocks, so many sick twisted freindly porsche gearheads...

Scott Wolthuis · 05-26-2005, 08:39 AM

The factory set-up...

The oil coming from the engine is first routed to the oil thermostat, at that point it either goes to the cooler or back to the oil tank or a mixture of both if the thermostat isn't fully open.

The thermostat has a pressure relief valve which will bypass the oil cooling circuit should it be restricted. So your oil pressure shouldn't drop. But you are burning power by maintaining a pressure adequate to hold open the relief spring due to the restricted oil line.

I repair 911 oil lines as a side/hobby...

I have the parts to build some for the 73 cars from newer lines... Anyone interested?

BReyes · BReyes's Garage

Oil Lines are a critical component of your engine's reliability. Always check your oil lines for restrictions due to driving (over speed bumps)and aging (oil debris or grime build up on the outside of the (rubber section of) oil lines.

Relace all oil lines that look old or damaged. They may fail in several ways that lead to oil starvation or overheating (and resulting damage) to your engine. Recent evidence of oil line problems leads me to even say to replace all oil breather lines, or any rubber (restrictors/ fittings/ hoses) in your oil cooling system.

I must say oil lines, including the system(tank, thermostats, senders,coolers) should be like new! In warm climates, I bring this to the top of my service to do list.

Just remember, you can never be too picky about it being right when it comes to your oil lines.

Regards