Extra coolant sensor to protect the head

[Randomg]

I was going through old receipts yesterday and realized the head I had to finally replace with a new one last year had been warped and/or cracked 3 times due to overheating. Twice by me. Both times in retrospect I should have known better. The previous owner had a repair record of a head straightening, valve seat removal, and new radiator. My first I had been refilling the reservoir every week due to a leak that became catastrophic, my second the fan belt broke and I drove to the closest gas station instead of pulling over.

My first thought is an extra coolant level sensor mounted to the bottom of the reservoir that's inline with a required electrical signal for the engine to run. That way if the existing level sensor comes on and this other one fires, you're not capable of ruining the head without first pulling over. You'll know what problem to look for and can make a judgment on if it's safe to disable this extra sensor until you can refill the reservoir.

Any thoughts on what type of sensor, which signal to tap into, or the best parts to tap into it with?

[Preyupy]

Does the stock level sensor work? Does the water temp gauge work? If not fix them, if they do work BELIEVE THEM. If you want an additional warning a water temperature switch set at 200-205degF in the water outlet pipe on the exhaust side of the engine would be my recommendation. Hook it to a big warning light! Water level is just one indication you have a problem, High temperatures are what cause you $$$$ problems.

[Randomg]

They both work, my fear is a bad leak that leads to both of them not telling you the severity of the problem. If your bottom radiator hose blew off for example and you were in the wrong place, you might drive a mile to find a place to pull over. Coolant sensors become inaccurate when the coolant isn't there to read in a bad leak scenario, and the coolant level sensor is more than 99% of the time a slow leak. Looks like at least twice in the car's lifetime, it's been a fast leak that ruins the head. If I'm the only one this has happen to however, I'll lean towards just keeping the cooling system in good order and pulling over as soon as either tells me something's wrong.

[Preyupy]

On race cars we use a pressure sensor in the cooling system set at 4-5 psi. When you start it cold the warning light will be on but once you are at 100degF you should have at least 5 psi and the light goes out. If you loose a hose, radiator cap or radiator failure you will get a warning.

[demetk]

On race cars we use a pressure sensor in the cooling system set at 4-5 psi. When you start it cold the warning light will be on but once you are at 100degF you should have at least 5 psi and the light goes out. If you loose a hose, radiator cap or radiator failure you will get a warning.

That's a nice add-on.

[gadget73]

Thats probably the better fix honestly. Losing water will make the temp sender not read. I popped a hose on a truck I had years ago and the gauge climbed a bit then dropped. At that point I knew it was basically empty. The cloud of smoke under the hood was clue #1 but I was on the up side of a heavily trafficked bridge and there was nowhere to stop. If I'd had something set up to kill the ignition in the event of an overheat there is a pretty high chance I wouldn't be making this post now.

[Randomg]

Had a racer friend recommend the coolant pressure sensor as the quickest responding and most accurate solution. How long do they stay on during warm up? I like the idea of the second level sensor not requiring much wiring or a light.

[tn535i]

Another thing... BMW updated the coolant temp sensor to also include a switch for an idiot or dummy light (what they used to call them) for people who don't pay attention to the gauge. My 88 M6 has this newer switch and warning light and I believe it fits in the same port on your T-stat. There is also very likely to be a blank bulb spot on your temperature gauge that was intended for this warning light. It light up on the gauge and works exactly like the low fuel warning light on your fuel gauge. You could consider updating to this but probably would need to run a wire for it.

[austin8753]

Another thing... BMW updated the coolant temp sensor to also include a switch for an idiot or dummy light (what they used to call them) for people who don't pay attention to the gauge. My 88 M6 has this newer switch and warning light and I believe it fits in the same port on your T-stat. There is also very likely to be a blank bulb spot on your temperature gauge that was intended for this warning light. It light up on the gauge and works exactly like the low fuel warning light on your fuel gauge. You could consider updating to this but probably would need to run a wire for it.

can you post a picture of this? i'm really curious to see how it was done.

[Randomg]

I feel like I saw that light go on once during one of the times mentioned in my first post, but I could be mistaken. Seems like splicing in a 2nd level sensor or pressure sensor into that circuit would be the least annoying light to have come on when the pressure is low during warm up. Nice suggestion.

[jc72]

Another thing... BMW updated the coolant temp sensor to also include a switch for an idiot or dummy light (what they used to call them) for people who don't pay attention to the gauge. My 88 M6 has this newer switch and warning light and I believe it fits in the same port on your T-stat. There is also very likely to be a blank bulb spot on your temperature gauge that was intended for this warning light. It light up on the gauge and works exactly like the low fuel warning light on your fuel gauge. You could consider updating to this but probably would need to run a wire for it.

can you post a picture of this? i'm really curious to see how it was done.

The sensor has an extra spade connector to trigger the warning light if your temp goes into the red.