1986 VW Golf is now in my possession.

[Christ]

I entirely removed the radiator fan. I'm going to replace the radiator with a much smaller one from a motorcycle, with a dedicated duct. The airflow won't have access to the engine at all, as it wil be ducted through the engine compartment to vent under the chassis.

[Deezler]

Originally Posted by Christ

Viscosity increases, so it's less likely to run out away from where it should be.

I've never had an engine that used significantly more oil or made more noise by going to a lower viscosity oil.

No no no no.... Frank had it right. Viscosity decreases in logarithmic decay as temperature rises.. Hot oil "feeling" thinner means it has lower viscosity and is more prone to flow.

In a vehicle, the oil is only going to get so hot (as regulated through oil-coolant heat exchanger). OEMs choose the weight of oil necessary to maintain appropriate protection at this expected temperature. Diesel engines in particular have very high specific loading on certain components, most notably camshafts. Changing viscosity on a diesel is a much more risky game vs. a low power gasser. Lots of people are pointing at premature camshaft failures as evidence of VW's mistake of supplying 5w-30 to dealerships for the PD (pump-duese) TDIs - they originally only used 5w-40.

Nice vehicle acquisition though, good luck modding. If you are ever less than 99% sure about something TDI related, do ask over on tdiclub.

[Christ]

Originally Posted by Blackstone website

The difference between multi-grade and straight-weight oil is simply the addition of a viscosity improving (VI) additive. The most common grade of automotive oil in use today is the 5W/30, which is a mineral oil refined with VI additives that leave it reading as an SAE 5W viscosity when cold, yet an SAE 30W when hot (210F). The advantage to the multi-weight is that when starting the engine, the multi-viscosity oil (with its thickness of an SAE 5W when cold), allows the engine to spin over more easily. The most common diesel use oil is 15W/40. It is an SAE 15W oil with a VI additive that leaves it the thickness of an SAE 40 weight at operating temperature. What makes an oil a diesel-use oil (rather than automotive-use) is the level of additives used. Diesels require heavier levels of dispersant and anti-wear additives. These heavier additive levels are objectionable for automotive engines since they may interfere with the emission controls mandated by the EPA.

This seems to disagree...

[Deezler]

Ah, I see where you are coming from.

Multi-grade oil are indeed designed to "appear", or behave as different viscosities as the temperature changes. This allows them to stay thinner at cold temps but not go way too thin even once the oil is very hot. However even with these characteristics they are still much thicker overall when cold than when hot. A quick google search found this image:

http://lh4.ggpht.com/_TcZIHGRFnvY/Sx...c/s512/oil.jpg

From this site:
Graph your oils

[Christ]

Ok, gotcha.

So, by the looks, I've got an oil leak at the head gasket... I cleaned the area up once, haven't really paid any attention to it for awhile, and it's pretty cruddy again. I may have spilled some oil and it just baked on there.

Still left to do:
Struts/mounts
Brakes (Rears, fluid/flush, rubber lines?)
Engine mounts
Exhaust header/2" straight into diesel muffler
Tires (need 2, getting 4)
Modding.

[Christ]

52.9 mpg!!!

[Deezler]

Most excellent.

[Christ]

I'm seriously thinking about putting a smaller fuel tank in it... So I can fill it up more often.

[MetroMPG]

52.9 - nice work.

Small tank = less weight... or you could just fill it part way.

[Christ]

Part way makes accurate results more difficult, and no available instrumentation here to go from.

One of my planned mods is an 8 gallon (6/2) dual tank system, which is just over 1/2 my current capacity of 14 gallons; an approximate weight savings of 30lbs, enough to justify installing a second battery and dc/dc converter, which should allow the alternator delete, leaving the only belt driven accessory as the water pump, a functional necessity.