TeamSwift

I just pulled the code P0117 which says in my Chilton book: "Engine Coolant Temperature Circuit Low Input"

The Temperature Gauge shot off the scale and I shut it down, I managed to get it home with "stop and cool" drive a few blocks and repeat.

The Temp. Gauge was acting a little strange a few months ago and it reported that I was "running hot" but not in the red. As a precautionary measure I replaced the Thermostat a few months ago with the more expensive 160 degree switch so that the Thermostat would open at that lower temperature rather than the usual 180 degree. That seemed to work fine for several weeks.

However.... the Temperature Gauge would occasionally shoot up near the red and then mysteriously return to normal, right in the middle of the scale. This happened maybe 6 - 8 times over the past couple of months. I took no action.

So the code popped up today.... crawling home with the "start & go and stop & cool method, I tried to "bleed" off some heat by turning up the defroster all the way to it's hottest setting and the blower fan to the highest setting....but the air coming out wasn't hot ??? I made it home...It was only 2 miles....but the engine was really, really hot....Fortunately the Radiator Fan was working fine.

Is it the Coolant Temperature Sensor which is located in the Thermostat Housing??? or... Is my Water Pump shot???

Or...Is it Both??? Or.. Is it something else???

Obviously, I can't drive it til I fix it...Your help / advice / assistance is much appreciated.

THANKS IN ADVANCE FOR YOUR ADVICE AND HELP.

You should put a description of what engine/transmission combination you have over there <<<<< in your profile because different years and different engines have VERY different cooling sensors. I can extrapolate from you providing OBD2 error codes that you've got a 96 or newer car, so in this case we're past that mystery. The sensor on the thermostat housing runs the gauge on your dashboard. The sensor on your throttle body (or maybe on the intake manifold right below the throttle body, I'm not sure) reports to the PCM and the PCM then throws trouble codes and turns on the radiator fan. Usually a code like this indicates a bad sensor or bad wiring between the sensor and the PCM. However, this comment makes me wonder:The fact that you weren't getting any heat out of the heater tells me that you are seriously low on coolant. Could be that you've got a slow leak and all the up and down over the past few months is caused by the sensor having coolant in contact with it at some times, but not at others. It's also possible that you've got a blown head gasket and sometimes superhot combustion gas is being injected into your cooling system. That could cause a high reading for a short time, and would also push coolant out into the overflow tank, eventually causing a low coolant level.

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Sorry I missed the car disclosure:

1997 Geo Metro Hatchback 3 Cylinder 5 speed manual transmission.

I opened up the radiator this morning (morning after the incident)....it was full so no leak.

I should report that the engine had gotten SUPER HOT...I.E. just a few little whisps of smoke on the belt side of the engine from under the throttle body somewhere. I couldn't even put my finger on the valve cover it was so hot.

It did start this morning ....I just turned it over for 30 seconds to see if I had seized the engine....sounded OK.

Besides doing a compression check...How do I determine if I have damaged the engine in any way such as: blown the head gasket or Burned the valves or damaged the cylinder sleeves or anything else???

If it is "Air in the Coolant System" can I eliminate that by starting the engine with the Radiator Cap off and waiting for the Thermostat to open and topping off the coolant as the bubbles make their way to the opened cap and escape???

Thanks in advance for your advice.

Good news...I think...

I checked the compression and it maxed out @ 180 lbs. on all three.

When I removed the Radiator Cap and relieved any residual negative pressure and there was a steady stream of coolant that leaked out from under the Water Pump exactly like this UTube video:

https://www.youtube.com/watch?v=B8t8DegIAEg

That strongly indicates that the Water Pump Oil Seal is shot and I need either a new Oil Seal or easier yet a new Water Pump.

Unfortunately I'm not adept enough to do the Water Pump replacement....I've watched the UTube videos and seen how a complete amateur like me manages to turn an afternoons job for someone who has adequate mechanical skills and the tools to do it into a 3 day nightmare with a busted belt cover (it is plastic).

I'm having it towed to my local Midas franchise who gave me an estimate of $315.00 complete. I know it's a lot, shop rate is $110 / hr. + parts...but I'm not competent enough to do the job.

Hopefully THAT'S IT..... I'll report back the final result when the jobs done.....I'd like to take this opportunity to thank all of you who responded and reached out to help me out...THANKS AGAIN.

It WAS the WATER PUMP and only the Water Pump.
$374.00 out the door.

Thanks to all who lent me their ear and assistance.

In the Fall I will need to replace front Brake Rotors and pads...
I'm thinking of doing that myself.