Is there a way to check the oil pressure on an E420 without spending major $$?

I am still puzzled with my oil guage. On cold start I idle at 3 bar for about 10 minutes then drop off to between 0-.5. Based on RPM's as I drive it is all over the place until I reach a temperature between 80c and the unmarked bar above 80c. Once there, the needle only leaves 0 when I am above 1700 RPM. I was previously have a heating issue in the 100c range for 2-3 days until I realized I had a blown fuse controlling my auxillary fans. Now that these are working, I never cross the unmarked line just above 80c. Typically halfway between 80c and this line..even in 5-10mph 5pm traffic at 90+ F.

Is it possible for the fans alone to maintain normal operating tempurate with little or no oil pressure? I would think the friction would override a fan's ability to cool? The fact that I am not overheating makes me think that something is suspect with the guage?

Is there a wire that goes to a sending unit that could be having issues? I once had a 66 Chevy pickup that had a single wire that went to a plug in the intake manifold that controlled the guage. That truck also had a wild needle depending on RPM's and did experience a grounding out effect that was traced to an exposed portion of insulation allowing the wire to touch the engine on occassion.

Could I have something such as this taking place OR can the fans really be that good at maintaining a cool engine with poor lubrication?

 

I cannot comment on your oil pressure issue except to ask how many miles are on the engine. As they wear and clearances begin to expand, thinner oils penetrate seals more easily and will not always generate the pressure necessary to fully lubricate all moving parts. Picture the lifters not getting enough pressure and letting the valves rattle, you can imagine. SO, short version: older/higher mileage vehicles start to want thicker (higher viscosity rating) oils.
What causes me to reply most is what you consider normal. I've only had my 420 for 2 months, and it seems to run in the 100c range, or at least it did. I think a transmission rebuild relieved most of that, I haven't watched as closely but it now seems to be 80-90c most of the times I look. I don't know what is considered normal operating temp range for this engine. Some like it hot, I thought most Benz' swung that way.

 

My engine has 128,000 miles. I typically used 15w-50 mobile 1. However, for my diagnostics I went with 5w-30 to see if I noticed any difference. My temperature only increased during the 2-3 days that my fans were inoperable. Once they were back in action my temp was back to normal. I am having no indication of lifter noise or other audible sounds of poor lubrication either. I also measure the oil with each change and I typically get 8 of my 8.5 quarts back over a 5,000 mile interval. That does not seem bad for 128k either.

I love the car, its smooth and strong. This issue has just plagued me for about a week now. When I noticed the change in the guage, the temp problem with the fans was right behind it. So I assumed the worst. Once I realized the fans had caused the temp difference, I was left with what appears to be low oil pressure without the affects of low oil pressure.