Coolant temperature?

[jcdavoin]

I have idle pb when the car gets really warm like city driving or traffic.So I checked my Coolant Temp sensor and the reading is good when the engine is cold but lower than spec (0.175 KOhm) after I drove last night. The spec shows 0.3 to 0.33 kOhm at 176F.I am wondering if the temp is getting higher than 176F to explain the impedance being lower?

Thanks.

[Q45tech]

My guess is that 175 ohms is at or just around 215-220F.

My guess is that the inside [not very fast responding or accurate] gauge is just into the overheat 1 o'clock position?

The ecu will not read any higher than 225F, as that is an extreme overheat and the protective ignition retard tops out at 215.0F.

Rad, thermostat, the usual culprits on a 9 year old car.

[jcdavoin]

Thanks for the reply.The inside temp gauge was at 3 O'clock when I read the sensor...What is an acceptable temp range for the coolant?Also, would the Coolant temp sensor affect idle speed?

And last, Do I need to drain the coolant to replace the sensor?...or is there a thermowell between the sensor and the coolant?

I am new to this forum and already getting much needed/valuable information.

Thank You.

[Q45tech]

Something doesn't sound right.........was the 175 ohms from the 2 terminal coolant temp sensor or the single terminal sensor that feed the inside gauge? there are 2 temp sensors and some 94+ with TCS/active have 3 temp sensors just for engine.

3 o'clock is the normal position.The Q is optimized to run at 176F and no more than 194.9F, ideally you would be at 180F cruising down the highway at 70 mph with AC on in 90F summer.

However when you slow down and idle in gear the temperature can rise 1,2-3F per minute...........not unusual for old dirty externally dirt plugged rads to run 10-20-even 30F hotter than ideal.

[jcdavoin]

Q45Tech,

The 175 Ohm was from the 2 terminals on the Engine Temp sensor, not the gauge.I will buy the sensor and get the proper procedure to change it.The coolant circuit has just ben drained 1 month ago and I don't know if it is required for changing the coolant sensor.

[Q45tech]

The only thing that counts is how what the ecu reads . The amount the resistance gets translated into a coolant temp by the ecu.

The inside gauge is so damped [slow moving and slow to change] that it is almost useless, except for reading: cold, warm/ok, and hot.

95% of the 6-7 year old Q I see are always above ideal temperature due to lack of maintenance and the slow progressive build up of dirt ,oxidation, fin bending, rubber surround deterioration.

Many non oem aftermarket radiators look the same but are low cost copies which may only work 90% as well as new oem, this coupled with therostats , cracked fan blades, sloppy installation, and engine coolant passage build up means the head temperatures may be hotter than designed even though the coolant temp may read normal.

[jcdavoin]

Thanks for the reply.I am looing for advice to change the sensor myself.Do I need to drain the coolant first? Or could it be done without draining then bleed the system from air.

Thks.

[Q451990]

I'm not entirely sure you need to change the sensor... unfortunately I have no idea on the J since I've never worked on one. On the Q it's mounted relatively high on the engine, so even draining out a little would probably leave it dry for a swap.

Hopefully someone else will come along soon that has done this on the J.

Heath

[Q45tech]

Also be sure to check the calibration of low cost VOM [under $300] as the published accuaracy may be way off with weak batteries.

[jcdavoin]

Thanks for the advice...I use a Fluke from work that is reading correctly.

[jcdavoin]

I should have described my pb first...Idle speed is good when the car warms up and is at temperature.If i am in traffic for some time or go shopping and start/stop the car over and over...well the idle goes low and it's like the car will stall. I assume a temp sensitive part would be involved like the Coolant sensor...I may be wrong...

[Q45tech]

As I pointed out the self protective functions of the ecu starts at 195.0000000000F and every 5F higher another degree of ignition advance is removed till 5 degrees have been removed at 215F coolant temp reading.

This is only self protective for a short time as the reduced advance shifts the moment of peak heat away from that optimized for the exhaust cam duration and after 5 minutes or so thermal run away begins AGAIN and there is nothing left for the ecu to do.......leaner mixture will run hotter and more fuel will increase the rpm thus generate more heat.

[jcdavoin]

So, the car is overheating and the ECU tries to compensate which gives bad idle...I should have the coolant circuit flush and radiator changed??

[elwesso]

What I would do is this (I did the same procedure)

Go out to autozone and get some ZEREX flush stuff (made by valvoline) and follow the instructions.. DONT get the radiator cleaner, make sure its the flush stuff....

Anyway, you put the stuff in the system, drive for a while (2hours or a couple days), and then do a full flush with distilled water and replace the thermostat.. That should take care of most everything, or at least tell you what your next course of action should be....