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Low Coolant Light

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Our 2000 Diplomat with ISC engine has an issue with the low coolant light. When starting, it comes on then goes off after several minutes of driving. The light will come on while driving, then go off. The plastic bottle is full. Coolant temps are normal. Is the sensor located in the plastic bottle? Thanks for the help.

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When you say that the plastic bottle is full, I assume that you mean that it is up to the full line - not totally full.

The cause could be any number of things. I has a similar problem when I bought my '97 Dynasty twelve years ago. I tried a lot of thing to fix it, including replacing the sensor. Nothing made any difference - and the temp. gauge never went higher than it should. Over time I started to pay closer attention to what was going on. When I filled the expansion tank (the plastic bottle) full enough the low coolant light wouldn't come on - for a while. Then it would intermittently come on and off - apparently at will. 

Eventually I determined that the "problem" was with the level sensor in the expansion tank - but it wasn't really a problem. It was just not perfect for my engine/expansion tank/sensor setup. What was happening is when the expansion tank was filled full enough to keep the light from coming, on everything was fine - until the water in the engine got hot and expanded. When that happened coolant got discharged from the tank until the level ended up at equilibrium between engine and expansion tank. At which time the sensor in the expansion tank showed "normal" when the engine was hot and "low" when the engine was cold.

The "normal" condition for the coolant level sensor in my coach is that it always shows low when the engine is first started. As the engine warms up the light goes off when the thermostat opens and the expansion tank does it's job. When the water in the engine cools the water goes back into the engine, and the light comes on. It's interesting to watch the difference between winter and summer when starting a trip: in summer the light goes out, and stays out, fairly quickly, while in winter the light cycles off and on for a long time before it finally staying off. It's also interesting to watch the behavior of the light as we drive over mountains, both in summer and winter. The light is always out when going up the mountain, and then goes on during the decent - more quickly in winter than in summer. 

Don't know for sure that this is the issue in your coach, but it's something to keep in mind.

Jeff Huntington '97 Dynasty 40 

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