Liquid Cooled ICE Question

[Renken2000Classic]

'75 SBC 400ci. 4-row radiator. It's in a P/U that gets maybe 1,000 miles a year. Weird question here, but I noticed Saturday that the radiator was full and under a bit of pressure when I opened the cap to check the coolant level (been sitting for a week). That radiator has a "Full Cold" line that's 4-6" or so below the neck, and the level is usually down in there a ways.

Only thing I remember doing is adding some to the overflow reservoir a while back (which prob had some in it), but I don't remember filling the radiator like that. Checked it today cold and same thing - chock full and under a bit of pressure. I know a certain amount of coolant is expected to move in and out of the overflow when it's hot/cold, and being full like that is totally normal for my other GM vehicles, but not this one.

The other thing... It runs just a little hotter than it used to, prob for a year or two now, like temp gauge up to the first mark (1/4 of the range or so), whereas it used to be a bit below that. Yesterday was about 90F and it was at that mark. I wouldn't think with a big radiator like that there'd be any reason for the normal running temp to climb unless it was clogged or the water pump wasn't working well or something.

Oil seems like just oil, coolant doesn't look oily. I wonder if the the trans is running hotter (400THM, and another story goes with that). It ran and shifted as expected, or as usual, when I drove it yesterday though.

I guess I could pull some out of the radiator down to the Cold line, make sure the overflow is at the Cold level too, and see what happens when I drive it again. It was just a surprise to find that and I took it to mean something had changed mechanically. Maybe I did it with the extra in the overflow though.

 

[Scott Danforth]

First, the bit of pressure is normal unless you check at the coldest time of day.

As the system cools, it draws in coolant from the puke tank (overflow)

As the day gets warm, the fluid expands and builds pressure up to the cap rating before it pushes back to the puke tank

So ignore that rabbit hole as there is nothing wrong there

Now on to running warmer. Siamese bores run warm. Motors that sit get growth on the walls of the cooling water jacket.

They used to put silicone crystals in coolant to "scrub" the water jacket. That just ate the radiators so that was shore lived

Best advice, drain the cooling system. Run a flush thru the system twice, then fill with new 50/50 mix

You will find the engine will run cooler for a bit until the growth comes back because the truck sits

 

[Renken2000Classic]

Ok, interesting points there. I assume (but don't know) the siamese bores thing is specific to the 400sb (like as opposed to a 350). Yes, it's been a while since it's been flushed.

 

[Scott Danforth]

Yep, only the production 400 SBC has siamesed bores where the 350 has coolant flowing between the bores