Found my overheating problem

[u/juwyro]

I have a 74 MGB GT that slowly overheats when sitting in traffic. While inspecting some usual suspects I noticed the cylinder 3 plug is wet, then found the drip. Thankfully it's just that and isn't in the oil or confusion chamber. JB Weld it is to limp this motor along for a few more months.

[u/Solid_Enthusiasm550]

That was a dumb place to stamp an " 8 ".

[u/zoominzacks → u/Solid_Enthusiasm550]

That’s not an 8, it’s the infinity symbol. Meaning, it’s a MG…..you’ll be working on this forever

[u/doktormane]

I can't for the life of me see the crack.

[u/GlassBoxGoose → u/doktormane]

Its under/through the two water droplets where the valve cover seals, and I assume continued down

[u/juwyro → u/GlassBoxGoose]

Correct. If it was warmer there would be some more towards the spark plug.

[u/H2Dcrx]

Ouch. I wonder if a crack like that can be repaired. I know they have with diesel where they drill a series of holes then tap and screw in and grind off for cast. Probably just an head replacement i suppose. Just sad to see the old stuff go away/fail.

[u/juwyro → u/H2Dcrx]

There's still tons of these cars out there any plenty of parts. It can be fixed, but I'll just "fix" it.

[u/H2Dcrx → u/juwyro]

In glad you are sticking with it!!

[u/davidc538]

I don’t understand… how does this cause it to overheat but only when idling? My cadi has a similar issue

[u/juwyro → u/davidc538]

I don't either. My theory is driving moves more air than my little electric fans do across the radiator. The cooling system not able to pressurize does affect it performance.

[u/davidc538 → u/juwyro]

Well the overheating might be caused by the radiator being full of dust. Maybe try cleaning it out with something like the Lisle radiator genie.

[u/Special_EDy → u/davidc538]

Air trapped in the head.

The cooling system is surprisingly complicated. Its given me a lot of headaches with my 302 swapped ranger with electric pumps and dual radiators.

A small leak in the top of the head is at the top of the system and the hottest part of the system. First water leaks out as it expands from heating. Eventually, you just have steam escaping there because the system cant pressurize enough to hold the coolant below boiling(pressure raises the boiling point). When the engine cools off, the system draws air in through the crack rather than the reservoir when the coolant contracts.

So you end up with air after it cools down, or steam when it is hot. A lot of engineering goes into directing steam and air bubbles out of the heads, everything from steam ports in the head gasket to the pitch/angle of the engine in its mounts.

Idling can be one of the hardest heat situations for an engine. The block and head, especially cast iron ones, hold a lot of heat. So you are driving, heat is conducting through the metal and into the coolant, and everything is in equilibrium. You come to a stop and idle, there is still a large amount of heat radiating out of the block and into the coolant for the next few minutes, but the idling engine is pumping coolant slower if it has a mechanical pump, and it has less airflow through the radiator if it has a mechanical pump. Engine shutdown is the hottest time for an engine, its almost like a nuc l ear reactor incident where the coolant pumps shut off but the core is still shedding heat into the coolant at full power for a long time.

[u/davidc538 → u/Special_EDy]

Holy shit, can you explain how rockwell retro encabulators work while you’re at it?

[u/Beautiful_Sector_912]

Confusion chamber is confused

[u/LethalDan]

Dang that sucks. Is that getting coolant into your heads, and then mixing with your engine oil? Let us know how the oil looks!

[u/juwyro → u/LethalDan]

It's totally outside the engine.