M42 Crank but no-start

[hexagone]

Non-issue....

Turns out that 30 year old cars really just don’t like -20 degree weather.

[Boris3]

Should be warmer today as the vortex eases! The downside is that if the car starts this might make it harder to figure out what was going on.

That said, sounds like two different issues. The no start could be fuel related, if you are getting fuel to the rail it might be worth throwing a bottle of fuel line deicer in the tank. Not sure how full the tank was before the vortex hit and there could have been condensation issues. The jumping idle while it was running could be icv sticking, temp sensor issues, hoses degraded by cold enough for vacuum leaks etc. With the short trips I'd also pull the vent hose off the valve cover and see if the blowoff sludge had frozen blocking the line. In general the short trips would not have been good.

The coolant / heat issues could be the coolant mix and level as you note, air pockets in the system and especially in the heater core (how was heat before the vortex), or near the temp sensors. Hard to believe you would get to normal temps after a short 10m drive. Having a temp gun to check the block would be useful.

If it fires up today with the warmer temps, and the coolant temps don't spike, drive it for a while rather than short trips. Now though we'll get rain and black ice. Be careful and good luck!