3500GT: problems with the regulator on the oil pump

I own an early 3500GT (VIN 566) of '59. This car has no external oil pump and the oil filter is in front on the right side (not mounted on the engine). The car runs very well, and the oil-pressure is between 3 and 6. When running on 800 - 1000 rpm the oil pump makes terrible vibrations. When I touch the hose leading from the oil pump back to the oil sump (not this one going to the oil filter) I feel a very strong pumping, which ends at app. 1200 rpm. Also on the second hose from the oil pump (leading to the filter) I feel a very little pumping, but not to be mentioned. From 1200 rpms onwards there are no vibrations at all. The hose leading to the oil sump feels very hard (seems to be full) and there is no punping any more. I checked the regulator on top of the oil pump, but for me it seemed to be OK. This situation did not change, when I screw the regulator up and down, so pressure was set more high (app. 5 bar) or down (app. 2 bar).

Is there anybody in this forum, who ever had a problem like mine and found a solution?

Thanks
Alfred

 

Hi Wilfried,
Yes, it is the rubber tube from the oil pump to the oil pan. But the oil does not flow from the oil pan to the pump it flows from the pump to the oil pan, because this is only an overflow tube. If there is too much oil pumped to the filter the oil gets back to the pan directly without going through the engine.

What we have done till now:
We dismantled the tube at the end of the oil pan.
We started the engine. A lot of oil (approx. 2 - 2,5 litres) have been pumped sporadically out of the car.
Afterwords there was no noise and no vibration any more. The engine rän very soft and well.
The only problem was:
The level on the oil level gauge was 2-3 cm beneath the MIN line.
That means: 2,5 liter oil were missing.
When we filled in 2 liter, the noise and the vibration started again.

We also changed this tube against a new one (harder rubber) but nothing has changed.

The noise does not not always exist (which means the vibrations are not permanently too strong), sometimes there is no noise for 1-2 minutes, but then it starts again. You can hear this noise ALWAYS at the begin (when starting the engine) and for a VERY VERY short time (1 or 2 sec.) when switching off the engine.

We suppose, the vibration depends upon the pressure coming out of the pump. Less pressure means vibration, more pressure - silence. But it does not really seem to be logical. What I could understand: Too much pressure - vibration, low pressure - silence? Maybe there is a permanent change between too much pressure and less pressure? But somebody must have known something when constructing this system?

I also have a 60 spyder, which has an additional external oil pump (only for cooling the oil).
The regular loop in this car is from the internal oil pump to the filter (mounted on the right side back on the engine. On top of the filter you can adjust the presure by giving more or less washers. In this car, the tube from the oil pump to the filter does not make any vibration or noise.

I do not have ANY idea - I am really at a loss !

Alfred

 

Hi Wilfried,
don't worry, the engine only run once for 20 or 30 seconds. I knew when the noise and the vibrations were gone, the engine had too less oil and therefore also LOW pressure. As I mentioned, I refilled 2 liter oil before starting the next test. I also made a reset of the regulator to 5 bar. Unfortunately the vibrations were still here.

I made a lot of attempts, so I cannot say definitely if there was the noise only when the engine was cold. I am sure the vibrations were at idle.

But next week I will make a new series of attempts:
1. cold engine at idle,
2. cold engine 2000rpms,
3. hot engine at idle,
4. hot engine at 2000 rpms.

I will report detailed results.

What I suggest is that maybe the tube from the pump to the filter is too soft (too much flexible). If the pump does not push the oil constantly (I do not know why this should be? but if it would be?) and the tube is soft, maybe the oil librates and this could create vibrations. I changed all tubes because the old ones were stiff. Maybe the new ones are too soft. Therefore I will reinstall these two old (hard and stiff) tubes (from the pump to the filter and from the filter to the engine) and make the same tests as described above.

I will post the results.

Any other additional idea what I could do, will be accepted.
Alfred

 

Hi Wilfried,
Thank you, this is a good idea. We will do that first of all.

Alfred