Overheating Puzzle
Under the Lift
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Joined: Mar 2002
Posts: 18,648
Likes: 52
From: Buckeye, AZ
Coolant around the back passenger side could be from a bunch of things in that area:
Leaky coolant reservoir
Leaky hose (possible loose clamp or small split) going to the bottom of the coolant reservoir.
Leaky heater control valve or hose to or from there.
Anyway, remove the air filter housing and feel the hoses and fittings in that area. You'll find something when you get a wet finger.
Your observation of the cold outlet hose from the radiator would be consistent with no flow - bad water pump. On the other hand, the radiator is supposed to cool to coolant. An IR temp gun is very handy. The inlet temp should be around 195F and the outlet about 45 degrees cooler. If the outlet is COLD when the motor is running hot, then, yes, you probably have a bad water pump (but see thermostat comment below first). In theory it could be plugged radiator, but that's rare. Normally with a bad water pump the coolant temp soars pretty rapidly.
It's always worth checking the thermostat, and replacing it is no harder than checking it. In the 928, the thermostat is ESSENTIAL, unlike many American cars, since in Porsche's design the thermostat doesn't OPEN the path to the radiator - instead it CLOSES off a radiator bypass channel. So, without the thermostat, the 928 overheats. Some people mistakenly remove the thermostat. For most model years there is a seal in the waterbridge that the thermostat closes against. That should be replaced as well.
Leaky coolant reservoir
Leaky hose (possible loose clamp or small split) going to the bottom of the coolant reservoir.
Leaky heater control valve or hose to or from there.
Anyway, remove the air filter housing and feel the hoses and fittings in that area. You'll find something when you get a wet finger.
Your observation of the cold outlet hose from the radiator would be consistent with no flow - bad water pump. On the other hand, the radiator is supposed to cool to coolant. An IR temp gun is very handy. The inlet temp should be around 195F and the outlet about 45 degrees cooler. If the outlet is COLD when the motor is running hot, then, yes, you probably have a bad water pump (but see thermostat comment below first). In theory it could be plugged radiator, but that's rare. Normally with a bad water pump the coolant temp soars pretty rapidly.
It's always worth checking the thermostat, and replacing it is no harder than checking it. In the 928, the thermostat is ESSENTIAL, unlike many American cars, since in Porsche's design the thermostat doesn't OPEN the path to the radiator - instead it CLOSES off a radiator bypass channel. So, without the thermostat, the 928 overheats. Some people mistakenly remove the thermostat. For most model years there is a seal in the waterbridge that the thermostat closes against. That should be replaced as well.
