924Board.org

[melon]

What is a normal speed for the temperature gauge to rise when accelerating hard? My car overheated a few weeks back. We just replaced some parts last night and I took it for a spin. I drove it like I normally do, except keeping a really close eye on the temperature gauge. I noticed the harder/faster I accelerate that the gauge will jump from just below the first mark to between the 3rd mark and the red zone. Then when I stop accelerating and cruise, it goes back down to between the first and second mark. What I would like to know is if the gauge is supposed to jump like that, I've never really noticed before ... and now after the overheating incident I'm rather conscious of it.
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1980 n/a with EDIS and Megasquirt II Injection v2.684 betacode.
Porsche - Live it, Love it, Fix it

[Roger]

The guage is jumping because the gounds are bad. You need to clean them.
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1981 924 NA

Some people are like Slinkies. Not really good for anything, but you
still can't help but smile when you see one tumble down the stairs.

[leadfoot]

was the temperature cold outside??
when driving this is enough to cool the engine with very low coolant levels... try bleeding the coolant system again as air pockets can cause the temp guage to go above normal operating temperatures. The wax element in the valve that is at the front of the head has problems with corrosion over time and cannot open fully, it's the spring that corrodes. This can also cause overheating and will occur at idle, the gauge will just keep creeping up slowly until it reaches redline and then starts dumping coolant through the overflow hose, you can generally hear clanging at this stage as your coolant pipes start moving around.
The owners manual says it is quite normal for hard driving to be operating the engine into the red zone. As long as it cools down after reducing driving hard it should be fine, but if this is a worry then you could install a cooler thermo temperature fan sensor in the radiator if your driving habits are going to stay aggressive, but make sure your not running the engine too cold during non agressive periods as the engine oil needs to be at the right operating temperature.
Leadfoot

[Min]

[Min]

[leadfoot]

hmmm... lets say the next level of driving from cruising is aggressive and after that is hard driving then...
from normal operating temp which is dead centre and driving with the revs up to 4500/5500 the temp rises quickly to three quarters during hard driving, give or take 10/15 seconds. In stop start traffic this is more likely to be the quicker as with outside temp having the same effect. Cooling down to be around the same time.
During the aggressive driving the temps would rise in about 20/30 seconds to peak between half and three quarter mark.
During a hot day and aggressive driving the temps can easily get to three quarters in around the same time...but in all scenarios unless its cold outside the temps hove at half way.
The test for the thermostat is to feel with the back of your hand the lower coolant hose, if its cold after reaching operating temps then the thermostat has failed. The bleeder hose will still get warm from the head connection being hot. Air in the coolant will more likely cause bad readings from air being trapped around the temp sensor at the back of the head, or cause the fan not to operate due to the same reason.
The only other thing i can think that causes slow cooling is calcium build up in the coolant channels of the block and head, this would probably cause operating temp to be slightly higher than normal.
My fan comes on just above operating temp, so that at idle the fan is not on until iv'e driven somewhere and then will operate and turn off after getting back to operating temp.
Leadfoot

[rockola]

[924guy]

my first thought was bad gauge grounding as well( pyrometer is a great thing to have if you own a 924, ones on my wish list, great for verifying temps, and making sure the sausage is properly cooked )With the additional info im also wondering if the cooling system simply needs to be bled. there are several places in the 924 that air can collect, and sometimes its difficult to get it bled properly, and takes a few tries. A very few have perfected using a mighty vac to blled the cooling system, and even a far fewer have collapsed their radiator because of it, so ive stayed away from that route.

Since this seems to be a persistant problem, id probably take it few steps further:

1. inspect all hoses , including heater hoses ( a little mirror makes checking the one behing the head easier, pray to the porsche gods its okay.) replace any hose that even looks suspect.

2. Ensure fans are operating properly, if you have that pyrometer you check the fluid temp and ensure the fans are comming on at the proper temp. jump the spades and the fan should come on as well... if you have a/c ensure both fans are working ofcourse.

3. check water pump for play, and belt for slack. replace as necessary.

4. remove thermostat, check for scale, and boil test it, twice. if its "yucky" theres allot more crud in the rest of the system. boil test it twice because ive had one that opened perfectly the first try, and was hanging up on the second..very strange but possible. i have it in my storage boxes some place, i actually saved it because it was acting so weird. replace as necessary.

5. Drain and back flush entire cooling system , refill with "orange juice" , the head is alluminum, these cars need a phosphate free cooling fluid. I also add a can of redline water wetter, great stuff... the over achievers will pull the radiator and have it flow tested, descaled or replaced depending on flow testing results.

6. bleed cooling system properly, check the bleeder cap for integrity and make sure its not sucking air.. were not done yet, but getting close..

7. if you were able to check you gauge against pyrometer readings, great! if not, id recomend adding an additional ground wire to the instrument circuit. just find the ground lead and piggy back a wire off the ground from the gauge, stick a female spade on it and plug it into the ground terminal on the firewall behind the dash ( clean this while your at it and coat with dielectric gel or vasilene.) you have less gauge jump and brighter lighting.

if after all this, your still running hot, youve either missed something, your timing is way off, or youve got a serious engine internal issue thats creating more heat than the cooling system can shed (like a blocked cooling path.) but chances are if youve done the above, youll barely be able to break out of the white zone on the gauge...and your engine will be nice and cool and happy..
_________________
Eric
78 924
82 931 SE "smokey"
99' VehiCross
Y2K Honda Insight
http://www.cardomain.com/id/924Guy
Performance by Pasha

[kewpie79]

This could simply be a clogged radiator. Has it been rodded out? many older cars get sediment built up and restrict coolant flow.
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1980 Porsche 924
1984 Pontiac Grand Prix
2003 Kia Sorento

[Chrenan]

Melon,

These four steps keep my car running at the 1/4 temperature mark regardless of how hard I drive:

1: Replaced stock thermostat with 71C thermostat.

2: Replaced stock thermo switch with 65-60C switch. Thermo switch is located on the back of the rad near the top on the driver side. Very easy to replace with the correct size wrench (30mm I think).

3: Bleed the coolant system. You never know, you may have a lot of air bubbles running around in there which can spike your temperature. Plus, bleeding the coolant system will let you know if your water pump is moving any coolant, or if it is broken.

4: Add a bottle of water wetter when steps 1 through 3 are OK. Water Wetter is the K&N Air Filter of the coolant system in that it may not help at all. I don't know if it actually does anything, but I certainly hope so because it is a little pricey.

Hope that helps...
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1987 951 - M193 Version for Japan

[Roger]

[Roger]