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My 987.1 recently had a massive coolant leak when the "closure cap" on the engine failed. In spite of the loss of coolant, the needle of my temperature gauge remained fixed at 175 deg. F.

Is there something that can be installed that would give an accurate temperature reading? A different sensor perhaps? I'd rather not try to add a second or a different gauge.

Thanks in advance.

When the car is cold does it still show 175°? Losing coolant due to a faulty coolant cap doesn't mean that the car overheated. It can happen because of air in the system and it can happen because the cap failed. Both are common.
Another coolant temperature gauge won't help in this case because with the loss of coolant there will not be enough coolant to circulate and thus it doesn't flow past the temperature sensor.

You can check the coolant gauge for signs of over heating due to say a radiator fan that no longer runs. However, I can tell you from experience with my Boxster and Turbo even with one radiator fan non-operational there was no sign of overheating even in 90F+ ambient temperature. Even A/C was unaffected: It worked just fine.

There should be a low coolant level warning light. So you can monitor the temperature gauge but you also need to be on the lookout for the low coolant warning light.

In either event the engine needs to be shut down ASAP to avoid overheating.
After another person pointed out the very large puddle of coolant under my car at a gas station where I was filling up, I added a gallon of distilled water just to get to my home. The next morning I had to add even more to get it to the minimum level it before I drove to my dealer. The dealer told me it was the cap on the motor under the engine cover that had failed.

The warning light on the dash never came on, nor did the warning in the computer that my owner's manual says should have been displayed. I'm hard pressed to believe that the car did not overheat in the absence of that much coolant.

Edited 1 time(s). Last edit at 01/04/2020 01:25AM by j.davis. (view changes)
>> I'm hard pressed to believe that the car did not overheat in the absence of that much coolant.
As Mark said, these cooling systems are over-designed, so in 'normal' driving it's highly unlikely the car overheated unless the coolant was so low the water pump wasn't able to circulate enough to cool the engine internals, so I wouldn't worry and I'd guess the temperature gauge was reading accurately.

Perhaps the question you should be asking is why your 'low coolant' light didn't illuminate? You say you added a gallon - the capacity of these cars is ~6 gallons, so losing 1/6 of the capacity feels like it should have triggered the sensor though I'm unaware of the actual threshold. Perhaps something to investigate.

Maybe, encause the cap was bad, you really didn’t add a gallon at all (most could have gone to the overflow).
The sensors are pretty accurate, and although they can fail, yours may be fine and the cap was all that was needed.
Keep an eye on it. I think it’ll be fine.
Happy Porsche’ing

Pedro Bonilla
1998 Boxster 986 - 308,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

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