924Board.org

xpernet · Posted: Sat May 08, 2004 5:22 am Post subject: Turn down the Heat!

Hey guys!

Ive got a problem. When i arrived home and turned off the car, it appeared that my 924 overheated eventhough the temp gague was underneath 1/2. Anyhow i discovered that the Radiator fan is dead! So now i can't drive the car. I can't even keep it idle for more than 10 minutes without over heating it! Do you know any radiator fan replacement for a '77 924? And do you know where is its Fuse located ??? My car is an electrical mixup. I just see wires all over the engine compartment. These 924s are weird. Despite of their annoying problems, we keep them.....
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1977 Porsche 924
Sunroof Delete
Megasquirt II EFI & EDIS
Carrera GTS / 944 Body

"If one does not fail at times, then one has not challenged himself." Ferdinand Porsche

924RACR · Posted: Sat May 08, 2004 5:32 am Post subject:

It's rather unlikely that the fan itself is dead, as they tend to be a pretty bullet-proof design. If they are, they can be replaced with aftermarket ones. However, you are correct to suspect wiring. After checking the fuse and relay, it's quite possible that someone else butchered the wiring. It is also possible that the radiator switch is dead, but that's a common VW part, as is the relay, and shouldn't be too hard to replace if necessary.

In the Electrical part of the Tech Section, above, there's a big how-to I wrote that covers, in detail, the fan wiring. Your challenge will be matching it up to the wiring that's actually in the car (after previous owners, PO's, messed it up)!

Edit: here's the link...
http://www.924.org/techsection/elect_diag.htm
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

When the cooling fan relay fails, you can still activate the cooling fans by switching the ac system on. You can also remove heat from the cooling system by switching on the heater full blast.

Test the parts before you panic or start buying.

Start with the cooling fan switch (thermofan switch).

Take a screwdriver, and short the two leads together. With the ignition off, the fans should start to run. If the cooling fans run at all, then the cooling fan switch is defective. If they run at the low speed, all you need to do is replace the cooling fan switch. If they run at the high speed, then the cooling fan relay is defective as well as the cooling fan switch.

Remember that if the thermostat is defective, and is stuck closed, the temperature gauge will not warn you if the engine is overheating. The coolant needs to be circulating to get an accurate coolant temperature reading.

Thermostats, and cooling fan switches that open or activate at lower temperatures are available. You should replace install the lower temperature parts when replacement of old parts is required. DO NOT buy the 160 degree thermostat. It is too cold. The heater and windshield defroster in your car will not work properly if you use the 160 degree thermostat. The 180 degree parts are what you want.

Diesel · Joined: 03 Nov 2002 Posts: 1061 Location: Ellington,CT

924RACR · Posted: Sat May 08, 2004 7:43 am Post subject:

gwsg · Posted: Sat May 08, 2004 2:03 pm Post subject:

First try cleaning the ground connection for the fan [should be a brown wire].

This has happened to me twice, the first time was the radiator thermal switch which is located at the top right of the radiator when looking in to the engine bay. You will need a large ring spanner to remove it, 32mm IIRC. The second time was the ground connection.

You should get the Haynes workshop manual as it will be a great help with all the trouble shooting you will be doing.

Cheers

Geoff
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My 80 924 loves me.

Magnus K · Posted: Sat May 08, 2004 5:48 pm Post subject:

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

Diesel,

The temperature gauge is designed to read the temperature of liquids (coolant) not air. No coolant, means the gauge will read low or not at all. If the thermostat is stuck closed, no coolant circulates. The engine overheats, boils the coolant out of the block, and the temperature gauge will not read a high coolant temperature.

My 96 Ford Taurus did exactly this to me this past Tuesday.

924RACR,

You may not realize it, if you have never stayed in the desert, but in the desert, while it can get real hot during the day, at night it gets real cold to even things out (can get well below freezing). I guess a none functional windshield defroster might not ever bother him (very little humidity to condense on the glass), but having a heater that works would be nice.

The 160F thermostat (along with the 180F thermofan switch) actually seemed to work fine until one time when I was driving towards the "Grapevine" on the I5 headed towards Santa Clara to visit some college friends, and we were stopped at the Summit for a couple of hours because the CHP was escorting groups of vehicles because of the blowing snow and low visibility. Sitting there with the engine idling, the air coming out of the heater was like I had the AC running (and my 77 924 did not have AC). The temperature gauge did not even read.

Diesel · Joined: 03 Nov 2002 Posts: 1061 Location: Ellington,CT

So, while your engine is warming up, and the t-stat is closed, does your temp gauge rise as the coolant in the block absorbs heat from the cylinders? Yes, it does. If the t-stat stayed closed, is the gauge in the car going to be pegged before it reaches 'critical mass' and blows the coolant out of the overflow? Yes, it will. Even if you dropped the belt from the water pump and there was no flow at all, the gauge will tell you the relative temperature of the coolant right up until lift-off. The only time that the (functioning) temp gauge will not alert you to an overheating problem is if something has taken the place of the coolant in the cylinder head where the sending unit is; if a headgasket fails and lets combustion gases into the cooling system this would be the case.
_________________
Dan Flanagan--2002 VW Jetta TDI, 83 Mercedes 300D,83 Mercedes Euro-240D

mick · Joined: 13 Jun 2003 Posts: 183 Location: ohio

thats odd my thermo switch went a few days ago also a new one was 7.00 bucks easy fix for once.
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80 931 intercooled,1 bar, and kinda runs right

kaffine · Joined: 13 Jun 2003 Posts: 644 Location: Las Vegas

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

At idle, the engine is not running under load, but it will still bring the operating temperature of the engine up to overheating without the water pump circulating the coolant, and the cooling fans tripping, over a period of time. My 81 924 will idle and trip the 180F thermostat and thermofan switch while sitting in my driveway, as will yours in about 15-20 minutes.

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

"The temperature gauge is designed to read the temperature of liquids (coolant) not air. No coolant, means the gauge will read low or not at all. If the thermostat is stuck closed, no coolant circulates. The engine overheats, boils the coolant out of the block, and the temperature gauge will not read a high coolant temperature. "

Umm, this is totally wrong. Just as Diesel said, if there is coolant touching the sender, then it will read correctly. The sender is on the back of the head. Coolant doesn't need to flow in order to get hot. The coolant will warm up just fine with the thermostat completely shut. And the gauge will show this (Diesel's "watch the temp gauge rise from cold" example).

You seem to be thinking that there is no coolant in the block with the thermostat shut. If that were true, then the gauge certainly wouldn't register a temp because it would just be reading off air.

I'm not sure what the warming up at idle example you give above is all about. Of course it will warmup. Internal combustion produces heat.

-nick

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

xpernet wrote: "...Ive got a problem. When i arrived home and turned off the car, it appeared that my 924 overheated eventhough the temp gague was underneath 1/2...".

This lead me to the idea that the temperature gauge is not reading correctly possibly because either the temperature sender is not continuously in contact with water, and/or because the thermostat has not opened to allow coolant to circulated and drive any air acuumulated form the head and allow full coolant contact with the temperature sender.

Most people do not keep their eyes glued to the gauges, I would hope that they are looking at the road/traffic. It is entirely possible that xpernet, did not look down at the gauges during the time that it took for the engine to overheat, before the coolant was blown from the engine, masking the overheating condition, because of the lack of coolant.

I never wrote that the coolant would not heat without circulation. I was trying to pass the idea that the gauge would not indicate the true and correct engine coolant temperature, without coolant circulation. No coolant flow creates localized hot spots where coolant will/could overheat, and flash into steam, raising the system pressure, and driving coolant from the system when the pressure cap opens up. At this point, the temperature gauge would not read correct with the additional cause (lack of coolant in contact with sender).