V8 Engine Coolant Light - LotusTalk - The Lotus Cars Community
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post #1 of 13 (permalink) Old 07-26-2019, 04:44 PM Thread Starter
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V8 Engine Coolant Light

Hi guys. Just got my car back from the garage and noticed my coolant light is lit up.
I've just had the round LED rear light panel conversion installed and wondered if they may have knocked a relay or sensor in the process of the install.
I'm not running hot and have not used any coolant. I'm not really worried that there is an issue with the cooling system, just wondered what could be a possible culprit.
I removed the float in the header tank and cleaned it out (a little brown debris in there). I have not yet cleaned the connections, but will get some contact cleaner on it tomorrow.
Seems strange that the sensor would go bad just sitting in the garage for a couple of weeks?
The expansion tank had only a little fluid in it after running for 30 mins, what level should this be at? If the expansion tank does need topping up, is it possible to do without removing the wheel?
Thanks in advance.
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post #2 of 13 (permalink) Old 07-26-2019, 04:59 PM
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Originally Posted by CookieGuy View Post
Hi guys. Just got my car back from the garage and noticed my coolant light is lit up.

I've just had the round LED rear light panel conversion installed and wondered if they may have knocked a relay or sensor in the process of the install.

I'm not running hot and have not used any coolant. I'm not really worried that there is an issue with the cooling system, just wondered what could be a possible culprit.

I removed the float in the header tank and cleaned it out (a little brown debris in there). I have not yet cleaned the connections, but will get some contact cleaner on it tomorrow.

Seems strange that the sensor would go bad just sitting in the garage for a couple of weeks?

The expansion tank had only a little fluid in it after running for 30 mins, what level should this be at? If the expansion tank does need topping up, is it possible to do without removing the wheel?

Thanks in advance.






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post #3 of 13 (permalink) Old 07-26-2019, 05:00 PM
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This happened to me as well. The float isnít working properly. I need to replace it or clean it well but havenít gotten around to it. Not sure if this is the issue but could be. Maybe you just didnít clean it enough?


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post #4 of 13 (permalink) Old 07-26-2019, 06:28 PM
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The header tank (the one by the motor) is supposed to be full when cold. The overflow tank (expansion tank) should be up to the full cold line (about 1/3 full) when cold. The light you are referring to is probably the level light and is lit when the level in the header tank drops. Easy to test, pull the wires to it, the light should go out. Touch them together and the light goes on.
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post #5 of 13 (permalink) Old 07-26-2019, 06:33 PM Thread Starter
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Thanks David, I'll test that out tomorrow.
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post #6 of 13 (permalink) Old 07-27-2019, 04:36 AM
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If you have a funnel with a long narrow tube you might be able to fill the overflow reservoir without removing the wheel. It might help to jack up the car a bit at the RR corner to get your hand in there.

But historically, you are best off removing the wheel, then remove and clean the bottle on the inside. (Use a brush for cleaning coffee pots) Otherwise you could mistake the 'scum' residue as coolant level.

It is also wise to tighten any clamps between the overflow and header tanks (if they are loose they could suck in air, when it should be drawing coolant back to the header).

Atwell Haines
'88 Esprit
Succasunna, NJ USA


"Not all angels have wings." - Turbo R
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post #7 of 13 (permalink) Old 07-27-2019, 04:19 PM Thread Starter
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I topped off the overflow reservoir to the required level (that was fun)
Cleaned off the electrical contacts to the coolant sensor. Could it be possible the wires have been replaced the wrong way around? Currently I believe I have a blue wire to the left and a white wire on the right.
Still the coolant telltale remains lit. It comes on instantly, so it cannot be due to excessive heat in the coolant.
Header tank remains full and overflow has remained half full. No coolant expelled that I have seen.
I cleaned the sensor yesterday in hot water, but that obviously hasn't worked. Is it worth trying to take the end cap off and take it apart to clean it out, or not worth the hassle?
According to one of the previous owner's posts on here, the sensor is less than 5 years old as they had this issue back then. Surely it should not have gone bad so quickly?
Thanks in advance for any help.
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post #8 of 13 (permalink) Old 07-27-2019, 06:07 PM Thread Starter
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Another quick test in the garage tonight. I tried running the car with the sensor out and me physically turning it upside down to see if the telltale went out.
It did not.
Switching the electrical connections around did nothing.
So I can only surmise that the sensor is bad, even though it is 5 years old at best.
The float appears to travel freely inside the sensor approximately 1 inch, is this about right?
What else could be broken inside there?
I'm thinking my only option is to order a new sensor, unless there is something I'm missing here.
Any ideas?
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post #9 of 13 (permalink) Old 07-28-2019, 04:40 AM
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If you are handy , you can take apart the sensor tube carefully and replace the the reed switch. I had to do this on mine, the coolant had leaked inside and corroded the reed switch.
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post #10 of 13 (permalink) Old 07-28-2019, 06:12 AM
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Isn't a properly working sensor supposed to rattle when you remove & shake it?

If you jumper/connect the sensor wires together, does the low coolant light go out?

Low Coolant conditions can gum up these sensors in short order.

Atwell Haines
'88 Esprit
Succasunna, NJ USA


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post #11 of 13 (permalink) Old 07-28-2019, 08:26 AM Thread Starter
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I removed the wires from the sensor, the light went out.
I jumped the connection wires together, the light comes on.
So am I correct in thinking it must be the sensor is at fault?
Thanks again
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post #12 of 13 (permalink) Old 07-28-2019, 09:24 AM
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That is the correct way to test the light circuit. If the light is staying on and the tank is filled, either the float isn't floating or the switch in the sensor is bad. Either way you have to repair the sensor (if you can) or replace it.
David Teitelbaum
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post #13 of 13 (permalink) Old 08-10-2019, 04:33 AM Thread Starter
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FYI, new sensor installed and all is working well again. Hard to believe a sensor only 5 years old would go bad so quickly.
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