87 porsche 924s. Cor overheating at idle. Coolant and oil look normal. No smoke. No heat coming out of vents. Replaced thermostat. Still overheats. Seems to have flow but not sure. It seems the heater core may not be filling and leaving air into the system. I am stumped.

Look close for oil leak from your valve cover on the exhaust.
check coolant with cold engine and top to max. next day recheck if yore losing coolant

the onlie last thing is to replace the thermostat. check the heater core/radiator.

Sounds like you have a leaking head gasket or damage to the engine from when it overheated.
A leaking head gasket can cause compression to leak into the cooling system and pull coolant into the cylinders which is burned out the exhaust. It does not have to leak into the oil.
A shop would check for exhaust gas in the cooling system and run a compression test on the cylinders.

Car overheats and Air blows hot at idle?

http://howtobyme.blogspot.com/2011/11/car-overheats-and-air-blows-hot-at-idle.html
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CAR OVERHEATING

There are many possibilities for car overheating.

Faulty thermostat clogged radiator/plugged radiator, radiator hose worn out. Coolant running low. Low coolant pressure. Faulty temperate sensor.

I suggest you to go through the troubleshooting details mentioned in the link below:-----

All types of car overheating problems and troubleshooting?

http://technoanswers.blogspot.com/2011/11/all-types-of-car-overheating-problems.html

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These will help.

Thanks.

Hi,

The overheating and lack of cabin heat both point to a failed engine thermostat which would be stuck closed. At the warm up stage, the coolant stays in the engine block to bring the engine to efficient operating temperature, then it opens and circulates the coolant through the radiator and heat core. If the thermostat is stuck closed, the engine will overheat, and coolant will never reach the heater core, and you will not get cabin heat.

Blinking oil light at idle which goes away during driving could be a low oil level, but may also be a drop in oil pressue. You could have a clogged oil fliter (at best) pickup tube, or a failing oil pump.

Overheating can seriously damage a car's engine if left unchecked. Although overheating simply means that a car's engine temperature exceeds normal operating temperatures, the causes of overheating are varied. What follows is a brief list of some of the most common causes of engine overheating.

Faulty Radiator
1. A car that overheats will often have a faulty radiator. A radiator is responsible for cooling hot engine coolant that picks up heat from inside a car's running engine. A radiator "radiates" the heat from engine coolant out into the outside air. A faulty radiator loses its "radiating" effects and allows engine coolant to become overheated, thus rendering it ineffective at adequately cooling and engine.
Faulty Water Pump
2. A faulty or malfunctioning water pump prevents adequate engine coolant flow and can cause a car to overheat. A water pump serves to pressurize and propel engine coolant throughout a car's engine and radiator to increase the heat-reducing capabilities of engine coolant. A faulty water pump loses its ability to adequately pump and propel engine coolant, and can cause a car to overheat.
Coolant System Leaks
3. A leaky engine coolant system reduces the level of circulating engine coolant, which increases engine temperature and leads to engine overheating. Radiators, water pumps, and coolant system hoses and seals--all of these coolant system parts can develop leaks, which can result in low coolant levels and engine overheating.
Faulty Thermostat
4. A car thermostat regulates the flow of engine coolant. A thermostat is a heat-sensitive valve that opens when a car engine reaches a set operating temperature and closes when a car engine is cold and warming up. If a thermostat gets stuck in the closed position, coolant will be prevented from reaching the engine, which will quickly lead to engine overheating and potential engine damage.
Low Engine Oil Level
5. Engine oil, in addition to lubricating an engine's internal parts, helps to keep engine operating temperatures reduced by eliminating friction within the engine. If engine oil levels are low, friction and heat build up inside an engine, a condition that causes increased engine operating temperatures and can lead to engine overheating.

Have you changed the water pump ?

Porsche 944 1983 model runs hot. When the fans come on it returns to normal but creeps back up and repeats.

First, plastic tube may be the overflow vent from the coolant bottle.Check to see where the attached end goes. You are going to have to check engine for coolant leaks (carefully refill system without spilling anything, then look for dripping anywhere. Look for leaks from all hoses, fittings radiator, water pump etc) After checking for leaks, start it up and check again (watch where you put your hands though) While running, check that the fan comes on when the vehicle reaches operating temp.(no fan, check fan motor, sensor & relay) Turn the heat on (does it have heat?) Check temp of lower hose and upper hose. If overheat happens, is lower hose still cold? (likely bad thermostat). If you found a leak, replace whatever is leaking...best insurance is to change thermostat after any overheat. Last, is there any white smoke from tailpipe, does engine run rough? If so, could be a failed head gasket or crack in cylinder head. (at this point last thing to worry about unless there is excessive smoke or rough run or oil in radiator or coolant in oil).