Temp jumps

[Jeffery]

Stop engine 5 mins after start bottom hose and radiator still cold . after setting for days outside temp and engine temp 30 degrees apart what would cause this

[BodybyFisher]

Check that the thermostat isn't frozen closed.

Then check to make sure the purge line flows.

Make sure the water pump belt is intack, turning and not slipping

Make sure the coolant is at least 50% coolant to distilled water.  

[Jeffery]

I put new failsafe t stat and new radiator new water pump belt and new sensor but it's not Really overheating computer somehow getting false reading 

[BodybyFisher]

Check for codes.  What kind of sensor?

Did you change the Engine Coolant Temp sensor?

See my signiture to see how to check codes.

[Jeffery]

Yes I changed engine coolant sensor purge line clear only codes are history p073

[BodybyFisher]

Ok, then, that isnt good.

Do you have a misfire?

What year car is this?

Are you saying it is not overhearing at all, but the instruments are falsely informing you that it is overheating?

[Jeffery]

94 Eldorado no misfire no overheat at all you can unhook sensor and drive all day with no problem do you suppose the end that hooks to sensor is bad ? I'm stummped at this point. it's a really nice car with only 140000 miles on it 

[BodybyFisher]

Ok, you have something going on, check the connector to see if its connectors are loose.    Did you have this before you changed the sensor?  You may have a bad connector, check the leads also for breaks 

P073 (E073) .....................................  Intermittent Coolant Sensor Signal

[Jeffery]

Its not loose I have checked all I know to check. would you recommend changing sensor end I replaced with duralast sensor . thanks for your time 

[rockfangd]

Welcome to Caddyinfo.

I only recommend oem acdelco or remy sensors as others are prone to not being close enough to spec to work properly.

did you put teflon on the threads? If so they are not meant to have that

[Jeffery]

Ok I'll swap for ac delco sensor but sensor already had tape on it. I put 2 sensors on both have done same anything else you suggest

[BodybyFisher]

Did you have this problem before the sensor was changed?

You never know, as rock says, it could be a bad sensor.

Do you have an ohm meter?  If yes, I can give you the resistance spec, to check the sensor.  But don't assume its good.

[Jeffery]

Yes I had same problem I do have meter . I believe there might be a short in the end of connector any easy way to get to it 

[BodybyFisher]

Ok, I have company that is leaving.  Ill pull my 94 manual and give you the resistance.

Ill look at the wiring diagram and diagnostic tree for P073 and report back.

[Jeffery]

Thank you 

[BodybyFisher]

Regarding the connector, its possible the connector is bad, Ill look at the manual to see what it looks like.  The connector may have female connectors that may be loose or corroded, you may be able to remove the connectors from the plastic plug with a sharp pick and tighten the female connectors.  You can buy a new connector also.  

[Jeffery]

Would that cause a 20 degree difference in sensor 

[BodybyFisher]

Well you are getting an intermittant connection, sometimes its connected sometimes not.   Let me look at the manual, Im trying to get my mother in law the H out lol

[Jeffery]

Ok let me know what you come up with please 

[Jeffery]

Would that give me false reading ?

[BodybyFisher]

I hope this helps, do you know how to get into the on board diagnostics to be able to monitor real time sensor data?

I believe you will get false readings, you will note that under "action taken" is NONE......, so there is no safety default of say 180 degrees or so.......having a bad ECT would be a critical failure condition potentially disguising a condition that could cause engine damage, so you will receive wacky temp readings by design that may set off alarms, etc.   By design, I believe it will keep trying to provide a temp as wrong as it might be.  The failure condition is the voltage changing 0.3 volts which equates to 11 degrees C or more in less than a second.  The intermittent code tells you that something is wrong.    We don't see a lot of ECT sensor problems.

This is just a guess, but something tells me that you are having a problem with your sensor. This sensor has a bit of complexity built into it because it has 2 ranges.    One of the worst types of problems you can diagnose is when you replace a part with a defective part, and proceed to tear your hair out because the problem still exists.   Start with checking the ECT sensor for resistance.  Keep in mind that it has two ranges, low and high.    Inspect the wiring in the area for damage and look for grounds, there is a ground in the area of the ECT sensor attached to the block make sure its attached solidly.

These diagnostic trees will help you navigate the problem.   I still need to get you the ECT sensor resistance range so you can test it.   Sorry for the delay, I have been hoppled badly with knee pain and have bad days.  Need surgery. 

 

[BodybyFisher]

I just looked through the manual and did not find any information on resistance.  That is surprising to me.   Ill look again, I recall in my 96 manual seeing a sheet of resistance specs for sensor testing.  I do have a 94 manual.  

I really like the 93 through 95 OBD1 cadillacs, the ability to get into the PCM parameters to monitor and override real time has always been intriguing to me.  Plus the PCM can be easily modified.   Cool stuff

Ill look again for the resistance specs.   But check the sensor, at room temp and at operating temp.  Can you get to the connectors with the sensor in place? 

[BodybyFisher]

With the attached information, you should be able to back probe the sensor using a digital voltmeter.  When cold you will have 5 volts with 0 volts when hot. I would connect my meter to the sensor return side or black wire according to that schematic above and the other lead to ground.   Watch the meter as the engine warms up, the voltage will drop, watch for erratic voltage swings as the engine gets up to operating temp.   The voltage should decrease steadily with no crazy behavior.

[Logan]

Pretty easy to find....

Search Google images: 'gm coolant temp sensor resistance chart'.

 

[BodybyFisher]

Thanks Logan, that's great.   I am sure its in the manual someplace, but have not found it yet.   thanks