Entire cooling system overhaul ... still problems

[MPrice]

Gentlemen,

I have a really frustrating problem with my 83 944na's cooling system. It is a project car and I have started the process of getting everything in working order. Problem has been that the car will overheat rather quickly. After running it long enough the temp gauge will peg to the extreme edge of the high temperature yellow box on the guage's face.

Between two different mechanics and myself the upper and lower radiator hoses, thermostat, fans, thermo-switch that screws into radiator, and radiator have been replaced. I was told by the second (good) mechanic that the head gasket was not leaking as they did a test there that showed no exhaust (i think) in the coolant system. The water pump is good, when i squeeze the upper radiator hose i feel a surge as I release my grip. Fans are both turning on.

The only thing I can think of are:

a. The temp gauge in the dash is messed up. (where is the sensor for these things located in the engine and does this fail often on these cars). Reason I think so is that the fan, thermo-switch, and radiator are brand new and the second fan does not switch on until the gauge inside the dash shows that the car is overheated. If the guage was correct wouldn't the fan come on much sooner? Plus there really isn't a "hot" feeling coming off of the block. I would assume, correct me if I'm wrong, that if the car was overheating to the extent that the gauge shows that there would be some percievable heat coming off of the engine, like "wow, thats getting hot."

b. Air in the system. Think this is possible too since reading so many posts here that suggest that this is a frequent problem. The '83 has that screwed up upper radiator hose that has a plastic plug in it as its bleeder valve. When I filled the car with coolent after I put in the radiator yesterday I pulled the plug and added antifreeze. I was hoping that the antifreeze would flow out of the bleeder hole before the coolant container overflowed but it didn't. I then ran the car, heater on full, with the bleeder open. It got hot enough until steam was shooting out of the hole and then started bubling a lil AF out so that's when i plugged it figuring that steam was any air left in the system. i think my methodology was flawed and after thinking about it I am going to try to stick a vaccum pump into the bleed hole ... suck until antifreeze flowsout .. and plug it quick. If anyone has an 83 or porsche with this type of radiator hose I'm all ears for any suggestions.

Anyways .. ats wits end .. any help would be MUCH appreciated

Thanx,
Mitch

[Andre]

prolly a bad gauge. most likely a bad ground. check the ground on block, when that is starting to get crappy the water temp gauge just pegs at the top.

[MPrice]

Ground on the block? I have replaced the ground for the negative battery terminal .. where are all the gauges ground to? I believe there is a seperate ground to the frame at the front driver's side of the car.

[Britwrench]

Is it really overheating or is the gauge reading wrong? Check with a temp gauge. Early 944 gauges can best be described as a "guide" and should not be relied on for facts.

[AFJuvat]

Agree on the "guide" on the early 944 gauge accuracy.

As britwrench said, is the car really overheating? are the fans coming on?

Couple of things to check:

Make sure your heat is on when you bleed. Bleeding is best done with the front of the car slightly raised. Steam is air in system - air is bad.

Sending unit for the gauge is right under the intake manifold for cylinder 1. Check the connection at the gauge - the sender may be faulty (PITA to get at)

There is a ground on the engine - behind the oil filler tube - located conveniently under the heater valve (which tends to leak with age) - thus corroding the ground - this usually causes a "hot start" problem

AFJuvat

[SoCal Driver]

Originally posted by MPrice
Ground on the block? I have replaced the ground for the negative battery terminal .. where are all the gauges ground to? I believe there is a seperate ground to the frame at the front driver's side of the car.

The grounds on the back of the block that go to the chassis.

As the temp gauge sender is a single wire unit there has to be another path for the electrons to travel. This sender is right behind the DME temp sender; under cylinder number one's intake runner.

Also take the slip on connector off of the sender and check the wire to it. This corrodes and has to be cut back and soldered back onto the special slip on that goes on the top of the temp sender. You may have to add wire depending on how far the wire is corroded.

Don't try to use any other slip on as this is one of those special jobies. You may have to crimp the sides a bit to get a solid grip in the temp sender.

Bleeding the system. Back the car down the driveway so the rear wheels are in the gutter and the front of the car is a foot or so higher. Turn on the heat to the interior. Take the plug out of the hose. Fill up the expansion tank and put the cap back on. Run the car till coolant flows out of the top hose plug port. Put the plug back in and tighten the clamp.

A much better bleeder is the ones off of the later models. This has a bleeder bolt in a 90 degree elbow on the engine. You may be able to find one of these fittings at a junk yard. You will also need a matching hose.

[Porsche944]

You need to bleed all of the air out of the cooling system, and then double-check the cooling fan operation.

The easiest way to bleed the system is to get the front higher than the rear, set the heater temperature control to full hot, open the bleeder, take off the radiator cap, put your hand over the filler neck, and then blow into the over flow hose. This will pressureize the cooling system and force any trapped air out of the bleeder. Once you get a steady stream of coolant, close the bleeder, put the radiator cap on and start the engine. Let the engine run for about 30 seconds or so, shut it down, and bleed the system again.

Both cooling fans should run at full speed when the engine is "hot" or when the A/C is on. One fan should run for a short time at a slower speed when the engine is hot and the ignition is off.

Clean the connector for the gage sender. The sender is located under the intake manifold between #2 and #3 intake runners. If you can get the sender out, test it in some hot water. The sender is an NTC or Negative Temperature Coefficient device, which means the device's internal resistance decreases as temperature increases. While you're at it, you might want to put a new spade connector on the sender wire.

Once you get that squared away, check the electrical system grounds. Since the sender uses the engine for one side of the electrical circuit, a bad ground path will cause the gage (and other components in the electrical system) to get really flaky.

[MPrice]

Thanx guys .. guess I know what I'll be doing this weekend

[SoCal Driver]

Just another thought; if you have pulled the wires on the fans lately check the fan rotation. You may have the wires on the wrong terminals.

[MPrice]

SoCal .. so if i reverse the polarity of the connections the fans will spin the wrong way? Interesting .... when i was hooking them back up i noticed that the wires could fit on either terminal .. they were both the same size .... the fan should be blowing air into the engine .. correct?

[SoCal Driver]

Yes the fans pull air through the radiator and onto the engine.

[bearone2]

if they are connected backwards the fan/s blow hot air to the front. i think the ground/brown is on the top and looking down from the front the fans should turn to the right.

[newoldguy]

Here's my experience--your results may vary. I did much of what you did in replacing a crapload of stuff, hoses, etc but my '87 was still running hot. To make a long story short, the brand new thermostat was bad and caused overheating. A second thermostat and snap-ring experience solved it.