Grabbed the second one... may as well change it all out. The bypass in my housing is completely plugged anyway.

Everything else flushed out without any debris or anything... though the block is probably just as gummed up. Who knows what the PO had done. Always an adventure.

Good time to replace the short bit of hose between the lower hose fitting and the thermostat housing. Since you're that far, if it's a pre '77 model, change out the fitted hose leading to the heater core return line (steel line on the right side of car which runs along the fender well).

I wonder how many others have a hole ready to open in their T-stat housing like yours. Aluminum is bad for corrosion in water, much worse than cast-iron or copper. The alum timing cover in my 1965 Chrysler V-8 looked fine on the outside but had 2 large holes about corroded thru from the inside. Most 1995+ vehicles have alum radiators which require regular replacement. I started using waterless coolant in most of my vehicles (incl. both 300D's), so will see if it lives up to its claims.

I'm dealing with a similar issue, just 300d with a neglected cooling system. Must have been watery coolant in there for years sitting. Orange thick corrosion in the radiator, water pump, hoses, and tank. Theres no saving these parts it is so thick that it just flakes off, and I'm not trying to clog up another radiator. Change your coolant people!

Yea, no rust in my system... the PO had some stuff done, including replacing the radiator, but other stuff was ignored. He only owned it less than a year and wasn't a wrench turner... bet that was expensive. :rolleyes:

Wow, that hole is amazing. Corroded right through.

I once worked on a 90s Honda at the shop. The inside of that cooling system was BEAUTIFUL. No corrosion at all, just shiny new Aluminum. The coolant was not rusty whatsoever. Just shows what proper cooling system maintenance is all about.

As unconnected as it sounds poor grounding of the electrical system is a major cause of cooling system corrosion. Research electrolysis.

When the connections become a bit corroded and the PH of the coolant reaches a sufficient level, the fluid becomes the transmission circuit. Most people just clean/check the main battery to engine block connection. There's a reason why all those extra ground wires are there.

Yea, I had an old Escort MR3 in England that actually had a steady 1.2V in the coolant in the expansion tank... my MOT mechanic actually called me over to show me. Then sold me a coolant flush by promising to fix up the electrical bugs along the way (and passing my MOT :D).

If you look at my first picture, the hole beneath the thermostat is full of what was caked on the inside of the cover (incidentally, the bottom of the cover, as mounted). As I scraped it away, the cover broke up with it. Didn't realize why the thermostat gasket had an extra hole until I started poking around in there. :rolleyes:

Seconded on this. I also have a VW Vanagon, and this is common practice on Vanagon aluminum cylinder heads. I repaired a set of pitted heads a couple of years back with JB Weld and they're still holding strong and are dry.

JB Weld might also work to seal off that hole. Emphasis on MIGHT. If I were in your shoes, I might try that first.

I only have quick set JB Weld on hand... Might have given it a shot if I had any 24 hour stuff left. The metal is really thin/brittle, but a thick enough plug, spread inside and out might hold... but I'm not quite that poor these days...