420C oil Pressure Low HELP!!!!!!

[jdman123]

I was running my 420c the other day for about one hour when
I noticed that the oil pressure guage had dropped from 21psi to about 15psi. I slowed the engine down and the guage red about 5 psi at idle. This dozer was not used much from the previous owner so I first changed the oil and filter and found sludge. What is the oil pressure supposed to be for these old machines? I heard around 30psi. I have bought two washers to add to the oil pressure relief valve, but I think the spring may be weak because there was already 3 washers In there. 20psi would be alright to me if it would oil the top of the engine good, but it is not. I have blown ou the steel line and it is clear, but no sufficient oiling. What should I do buy a spring and try that. This engine does not burn oil or smoke. Help!!!

Shawn

[Lavoy]

I think 20 PSI is about the high end for a 420, so no big deal there. The oil line to the head is a VERY low flow line, as long as it spurts a little oil, it is fine.
Lavoy