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Old 10-30-2003, 10:43 AM
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Join Date: Sep 2003
Posts: 222
420sel coolant light

My 86 420sel is showing a coolant light intermittently. I have added extra coolant two days ago and now the light is coming back. What should I be looking for to fix this? It has a new thermostat recently? Don't know where to start?

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Old 10-30-2003, 11:13 AM
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Join Date: Jun 2001
Location: Northern Calif. (Fairfield Area)
Posts: 2,225

If the thermostat change was recent recent, you may have had a little trapped air in the system which finally burped. I'd just wait and see if it comes on again assuming your temp reading is normal. If ithe light comes on again, I'd either pressure check or replace the rad cap. This cap doesn't just close off the hole anymore like the old days. It has to be able stay closed under pressures up to 140 kilopascals. If it doesn't hold, you will loose fluid. The next step would be to do a system pressure check for leaks. First of all don't pressurize over system pressure or you might be buying a new heater core. Secondly you can't pressure check a hot system. The system must be cold or there is a chance you won't find the leak. Good luck,
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Old 10-30-2003, 05:05 PM
sixto's Avatar
smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 18,745
Try cleaning the connector at the coolant level sensor.

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91 300SE
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Old 10-31-2003, 02:57 PM
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Join Date: Sep 2003
Posts: 222

I think I see a leak under the car, not at the radiator though. Have to get under this weekend to see. In the mean while, I'll have to keep adding coolant.

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Old 10-31-2003, 03:03 PM
G-Benz's Avatar
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Join Date: Apr 2001
Location: Dallas/Fort-Worth
Posts: 5,711
Your coolant level sensor is probably leaking at the seal if the coolant amount seems to be trace amounts over a long period of time. The coolant residue corrodes the pins and causes a faulty reading (i.e. the light comes on).

About $40 for the part at FastLane and 15 minutes of DIY will do the trick.
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Old 11-03-2003, 03:48 PM
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Join Date: Sep 2003
Posts: 222
found leak

I found the leak at the hose going from the radiator to the engine on the engine side.
The hose clamp was stripped and was partially tight. There was no leaking when the car was parked or after short trips. When the engine really heats up to operating temperature, it would leak probably when I am driving. Just put new hose clamp in. Hopefully, no leak anywhere else.

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