Hey there,
so I drove my 1996 Volvo 850 yesterday, it was running for good 40 minutes. after this time I stopped to put something on the roof and suddenly I heard a dimmed but still very clear blow/crack and blue smoke started coming from under the hood! So I stopped the engine immediately and looked under the hood. There was just a ton of smoke coming out of there. The most, however, when I opened the oil cap.
Please help! what could it be?

 

Hi and welcome to the site.

I doubt anyone can help you with what "might" be. You need to check the car over to see if there is some coolant or oil leak somewhere.

Is the car turbo? Do you see any fluid leak? Miles? PCV health?

 

Hi and thank you!

I just bought the car 2 weeks ago. There is no coolant leak. There is a little oil leak. When I bought it I was told that it'll need new PCV soon. So I am planning on doing that next week. It doesn't have turbo, and it has 190k miles.
I tried to turn it on today and it started right up, without any smoke or weird noises.

 

So I finally had time to look under the hood about three weeks ago! I was planning on replacing the pcv system anyways. the pcv was in a very bad shape, the pipes very clogged up (almost 2/3 of the pipe).
What caused the blue smoke? since the whole system was so clogged, the pressure increased to such level that the pipe that leads from the pcv valve into the head of the engine couldn't stand it and popped off of the head.
Anyways, I cleaned everything, replaced everything that needed to be replaced and it's running smooth again

 

Good deal, now check the heater core and other coolant related things.

 

That would have been my second question. (I am not sure whether I should create a new thread about it..?)
Yesterday I turned on the heating for the first time since I bought the car about two months ago. However, only cold air would come out of the blowers. Is there a way how I could tell whether it is the heater core or whether it is something with the regulators, or what else the cause could be?

 

You can check to see if the core has been bypassed.

 

I checked the pipes and they were not bypassed.
Also, in the meantime the alternator went out, so I replaced that, plus the serpentine belt using one of your videos!
now I'm focusing on the heat again. as I said, both pipes lead through the fire wall towards the heater core. However, (and I don't know if this is normal or not) I can easily turn the heat controller pass the 84 F mark. Could this maybe point at what could be wrong?

 

Could be loose ****. Are the pipes going into the car getting hot? Is the AIR MIX vent closed on the dash?

 

The heater core was not getting hot, neither were the hoses leading through the firewall. So I dug a little deeper and found that the hoses were just hanging there from the firewall loosely. The person who owned the car before me probably just cut them off, let them there and bypassed the heater core.
according to your video, can I assume that since it was bypassed, the heater core was leaking? in which case I'd just buy a new core, hoses, replace it and it should work?

 

You can probably use the hoses that are there and put a pipe to connect the splices. And yes, the heater core is likely leaking.