6.2L newbie question.

Hello all, (I accidentally posted this in the 6.5L yesterday)

This feels like a 'Step' program. My name is William and I just bought my first 6.2L. Precisely it is a '88 Chevy Step Van P20 with 48k miles. I acquired it at a govt auction, where in its previous life it was used for a security or range vehicle @ Sandia National Labs. It had rifle racks for 24 M16's and various shelves. I will post pictures in the near future.

I drove it back from NM sight unseen, 1100+miles just stopping for relief and fuel.... NOT a fast vehicle. 21hrs later I was back home. Good news, I made it. Bad news: slight overheating/instrumentation issues (speedo, and more).

I dont think the van wanted the trip to end, when I was within miles of home, I slowly lost power and I heard this weird howling noise, which I believe has to do with the water separator.

Fortunately for me, the very little prior reading I did on this engine showed me where the fuel filter was. After a quick drain and a little cranking it fired up again with out issue. I broke the #1 rule of owning a diesel -NEVER buy fuel at a small barely used station- which is precisely what I did near Bakersfield at a empty fruit market... oh well, not the van's fault, operator error.

Ok, my question(s): The van mechanically seems in rather good shape. While investigating the overheating issue, nothing I have read explains what I see when I pop the hood. On top of the radiator (which has no filler neck or cap) sits a cylindrical Harrison expansion/surge tank (with a filler port and cap) connected to that is the coolant overflow. The radiator cap that is on the expansion tank clearly says "No Vacuum relief". When the vehicle cools down, the top radiator hose collapses under vacuum. If I open the cap (when cooled) the hose returns to normal. From my reading, a typical radiator has a vacuum relief port built into the cap. But because of the strange config of this cooling system (which 'looks' stock BTW) I'm not sure if the cap is wrong, or I have another problem.
Thanks!

After downloading the 1986 Repair manual, it is called an aeration tank- intended to removed dissolved oxygen from the coolant. Why the P-series vans have it, and other vehicles don't I dunno. I also solved my over heating issue by replacing the cheap-o thermostat that was installed with a ACDelco 131-91. Now the vehicle temp gauge does not quite make it to the center line which is a huge improvement. I also took the opportunity to replace all the hoses and flush the coolant.

As an experiment, I boiled the old thermostat on the stove. It didn't even start to open at 200+!! So I took it outside and subjected it to a MAP gas torch. After the wax melted out, it opened and closed. When the new thermostat came in, I also boiled it on the stove. It seemed to start opening around 180. The thermometers I used are for cooking and not calibrated to any degree.

Did you clean you stack while working in it?

Between radiator, oil cooling coils and ac?

Often a trap for dirt, leaves, straw, pine needles.