Just finished doing a bunch of gaskets on my 1981 Econoline, 300 six. Did valve cover, pushrod cover, timing cover, and oil pan. Also replaced the water pump. Finally, got it all together the other night.
Added oil, and coolant. 6 quarts of oil, but only had 2gallons of coolant on hand. Filled the radiator to the top, with maybe a quarter gallon of coolant remaining. Fired it up.
Here’s where it gets weird. I was running the engine with the rad cap off,waiting for the level to drop when the t-stat opened. After about 5 minutes of running the engine, steam started blasting out of the open radiator. Shut engine off, and waited for steam to dissipate (maybe 1 min), added remainder of coolant on hand, put cap on radiator, fired it up. All gauges read normal.Walked around the front, and now both the upper and lower hoses were completely sucked shut, as in collapsed. Shut off engine. Waited a few minutes and then removed rad cap. As I did the system sucked air hard, and the hoses shaped backup. Coolant was low.
Picked up tools.
When I went to start the engine, just to drive the van out of my buddy’s driveway and park it on the street it didn’t want to start. Had to try a bunch of times before it finally went. I am planning on heading over today to top off the coolant, and run it a bit more. See what happens.

Wondering what the steam, and collapsed hoses are about though. Thanks inadvance.

 

Coolant capacity for my 86 5.8l is 2.5 gallons, I can't imagine yours being more than that. Did you also fill your coolant overflow up as well? The only thing that I can think of that would cause the vacuum in the coolant system would be a bad radiator cap.

 

There is no overflow on this van. All I see is a hose coming from the rad cap, which apparently dumps onto the street.

 

Also, factory manual lists cooling capacity for 4.9L (300 CID) at 15 quarts, which converts to 3.75 gallons.

 

I took a look again at my old pics when I disassembled my van and realized that mine didn't have coolant overflow either.

 

The 2.5 gals that I mentioned was from Auto Zone so it's a good chance that the factory manual says something different for mine.

 

Checkout the video that annaleigh posted in this thread, might help you double check your issue.

https://www.ford-trucks.com/forums/1...ted-today.html

 

Well, I went back, topped off the radiator, and fired it up. Ran it for a while as I checked various areas for leaks, etc. Ran it up to temp. and then some, no leaks observed, all gauges reading normal. Shut it down. Waited for it to cool down, checked oil and coolant levels. Levels were good, and no signs of mixing.


Drove it about 10 miles home with no issues. Checked everything again. I have a shot wheel bearing on the front right, so I haven't driven it much. But so far, it seems fine.

 

check your oil cap for foaming and maybe smell it for antifreeze....OR just change you oil / filter and see if there is any emulsification....I had a bad gasket 4 Vans ago and I ignored it and I eventually put a window in the block... It had over 500 k on it so I was not surprised....best wishes