My almost new SR3XX: I originally changed GDU oil after 3.5hrs, oil return line from the cooler entering the top of GDU pumped oil when spun the wheels (found out hard way). Now, at ~8.5 run hours, changed the oil again, can not get flow from return line on top. I tried spinning the wheels, even ran engine for 5 minutes in gear, a couple times, cant see any flow at the top.
I thought this pump was 100% mechanical. Is flow regulated somehow via thermostat or RPM? Both fluid flushes, no metal or particles in oil or magnets, no signs of any issues. I dont want to close up until I see flow again.
Any ideas what is going on? Purge air somewhere?
Also, please educate me:
Is the GDU pump entirely for fluid circulation and utilization of the cooler? Or, is the pump critical for lubrication of internal parts?
A rear end on a car is sealed system with only fluid circulation via sloshing and gears slinging it around. This oil viscosity is normally Ok without cooling in other applications. Maybe the gears of this Radical car are so severe they need it.
@raider89, If you have the GDU full of fluid (to the bottom of the overflow hole) and you are not getting fluid through the return line there is something wrong. To trouble shoot it, I would remove the pressure line and rotate the wheels to see if you get flow. If you do you may have an issue in one of the lines or the cooler. If you don't have flow your problem is likely the pump.
The purpose of the pump is to circulate the oil through the cooler, and it isn't required to lubricate the gears. Phil told me that they had to add the pump and cooler because they discovered in early testing that the GDU gets way too hot without a cooler.
Thanks, I thought it was for cooling only.
SOLVED:
I talked to a Radical race team in the UK, explained the issues. They had an interesting take. They had experienced similar issue trying to get flow for some unknown reason in the past. The pump moves extremely slow, and can loose prime. When/if a car is running on track sloshing and going thru the gears, the pump gets primed naturally. When simply on car lift, can be difficult to get pump primed when only spinning wheel or running the car slowly in 1st or 2nd gear. Even after several attempts. They said to actually run the car up thru the gears into 5th and 6th gear which would spin the pump much faster at 2,000 rpm. Boom - worked perfect.
They also had interesting comment about the factory. When building and assembling the car, they simply put fluid in GDU, close it up, and dont actually get flow themselves before sending to clients.
So, all my worries averted, have flow, closed up and ready for next event. BTW: I did all this because I installed a Tim Gray filter system to help preserve the GDU long term.
@raider89, Thanks for the update. I am glad to hear the issue is resolved. I had never heard that before. I am sure others will find this useful in the future!
@raider89 ... good to know and appreciate you sharing your experience.
I had been told that you should never run the car in gear while on air jacks or stands. Having seen other similar cars running in gear, I have noted they mostly say to remove rear wheels and its OK (to remove rotating mass and reduce chance of drivetrain oscillation starting)
How did you run your car up in 5th/6th (I guess at just above idle speed?) to check the pump? Did they give any guidance on how to do that?
That race team says they do it all the time, partly to confirm shifting prior to sessions. My car was on 2 post lift, wheels off, ran up gears at ~2,000rpm. Keep in mind, I had attempted to get fluid flow 3 prior times at idle in 1st gear for 5 minutes each. This only took ~1minute and was flowing oil. Just one time up the gears.
@raider89 .. Thanks Dan - I'll give it a try. I've got to run my car soon again anyway to re-balance the throttle bodies.
I'm guessing you sit in the car while doing this and use the clutch to downshift (and maybe upshift too?)... otherwise the downshift blip (with ~25% throttle action) might cause a fair 'shudder' through the drivetrain?
