I have an 87 924s that’s been in the shop and not driven for the last 3 years due to wiring issues. Now that she starts and runs, she’s running hot and I notice the antifreeze needs to be replenished. I’ve been told that if the head is made out of aluminum, I should use orange antifreeze and not green. Is this true?
Why does the coolant need to be replenished? Do you mean that the coolant is disappearing or just in need of a change? Universal green coolant is fine for this car. By “universal” I mean the stuff that can be added to any of the colors of coolant on the market.
What color is the coolant now? Green? Orange? or mud brown? BTW, “mud brown” is an indication of a problem as is disappearing coolant.
It’s green now but very low.
That’s not true.
When your vehicle was built back in 1987, the only antifreeze available was the green antifreeze.
So you can use whatever antifreeze you want.
Tester
Add more green but keep an eye on the coolant level. If you need to keep adding coolant, there is a problem. If there is a green puddle, you have an external leak - hose or gasket or water pump seal. If there is no evidence of a puddle, you have an internal leak - cracked head, head gasket, cracked block, really bad things. That may be another reason it was parked.
Thank you, now I have to say ‘innocuous’ because I didn’t have 10 characters in my reply. 
No, it was definitely parked because the wiring harness was toast. I appreciate your input!
As a 30 year old car that has been sitting for three years you need a serious cooling system service. at the minimum a chemical flush (see what VW recommends)
then fresh coolant.
I thought the OP has a 924 Porsche so why VW.
VW owns Porche, if OP had a Chevy I would say check what GM reccomends
VW did not own Porsche in 1987 so it only makes sense to check with a Porsche dealer or Porsche mechanic.
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I had the same vehicle with the same symptoms. It turned out to be a bad water pump.
Correct, but the engine was sourced from VW. Not until the 944 was the engine an actual Porsche.
I expect an 87 924 could use the ordinary green coolant, but it might be a good idea to drop by a VW dealership parts dept anyway. Ask them what kind of coolant they recommend for your 924. For Toyotas anyway, the price of coolant at the dealership isn’t much more than at an auto parts store, and when you buy it there you are sure you are using the correct coolant for the vehicle. It sounds like a cooling system flush is in order anyway at this point.
The 924S and 944 used the same engine, a 2.5L Porsche design.