In addition to the earlier mention of an alternator, I would offer to look at the starter. I've had similar experiences with my '92 245 and '90 760GLT that were resolved with a starter/solenoid replacement. I had no problems starting up the cars in the morning when ambient outside temperature was below 90F and not yet driven. With this "low" temperature, the starter/solenoid were also at ambient. After driving even only 20 minutes, the engine bay temperature would heat up and that meant the starter/solenoid did as well. I might shop in a store for no more then 10 min and the cars would not start after my shopping. I did several "simulated" shopping runs, always parking in my driveway after a 5 mile drive. After a 10 min, I'd attempt to start. Of course it didn't. Then I used my garden hose with a spray directed at the solenoid to cool it off. Once solenoid temperature got down below 90F. the cars started! I used a laser remote temperature sensor to measure temperatures in the engine bay and solenoid.

It reminds me of Machineman's excellent explanation of how a coil works or doesn't.

For the fun of Volvos,
Mike



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'92 245DL, '90 760 GLT