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Discussion Starter #1
I've been having an issue with my coolant temperature readings. It started to read high one night. Then it started to do it more often.

Car is bone stock.

I've replaced the coolant temperature sender that screws into the head. I've replaced the fan switch that screws into the t-stat housing. I've replaced the t-stat and I've also put a different radiator in it. Same problem.

I've ensured all the air is out of the system several times (by leaving cap off and letting it get to operating temp, squeezing hoses etc).

I am at the point where I think the guage is reading incorrectly. Here is my question. The 1 wire that comes from the teperature sensor in the head goes where? Is there a sending unit that could be bad? Something that lies between the sensor and the guage on the dash?

Thanks!
 

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Discussion Starter #3
wow way to throw money at it lol buy a chiltons man
Im throwing parts at it, not money. My friend has the exact same car, except he blew it up with a turbo. Talk about throwing money away.

I take it you dont know the answer to my question?
 

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68 Camaro
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did you replace your ect or you rgauge sending unit


cause i think you replaced your ect
 

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Discussion Starter #7 (Edited)
that one wire connection needs to be good, if its corroded at all you will have issues with your temp.
I think that could be the issue. The distributor leaked a small bit of oil onto the coolant temperature sensor wire. I'll take a closer look at that.

did you replace your ect or you rgauge sending unit

cause i think you replaced your ect
I replaced the coolant temperature sensor that screws into the head just below the distributor.

i think what cmgreen50 is saying is that its beter to diagnose the problem before your just start changing parts.

Is your fan even coming on?
I agree. It sure would be nice to know what the actual problem is.

The fan comes on.
 

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97 honda coupe
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I think that could be the issue. The distributor leaked a small bit of oil onto the coolant temperature sensor wire. I'll take a closer look at that.



I replaced the coolant temperature sensor that screws into the head just below the distributor.
there are two sensors, a two pronged sensor for the ECU and a 1 pronged sensor for the gauge unit on the instrument panel.
 

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Discussion Starter #9
there are two sensors, a two pronged sensor for the ECU and a 1 pronged sensor for the gauge unit on the instrument panel.
Interesting. I replaced the 1 pronged sensor.

If I had a scan tool I could see what the ECU temp was reading and compare that to the instrument panel. Unfortunately I dont have a scan tool.

Good to know there are two though.
 

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Discussion Starter #12
Coolant circulates (hoses both same temp) and the water pump was replaced about 25k miles ago with a new one. I have taken the all the air out of the system and verified a few times.

I haven't seen any of the normal indication of a head gasket (oil in coolant or coolant in oil).

The coolant temperature gauge in the car has some rapid fluctuation that reminds me more of an electrical thing. I replaced the thermostat and the exact same thing occurred.

I thought I had replaced the coolant sending unit but as asked above it was the ECT. I'll replace the sending unit and see what happens. If that doesn't fix it I'll get a leakdown test done.
 

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Discussion Starter #13 (Edited)
Its the head gasket. (or cracked head) I am thinking air bubbles are getting into the head which is causing my erratic readings. When I top off the coolant levels it stops for about a week of daily driving (80mi). Then it starts again. There are bubbles in the overflow tank and slow loss of coolant.

The engine had a slight mis-fire one morning that cleared up. I assumed that was a fowled out plug due to coolant that cleared up once it was warmed up.

Time to find a head gasket write up.
 
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