Van-Isle

hey all, Long story, but hopefully somebody'll read it all thru and help me out..

95 b18b1 LS, 230ks..

heater this morning was really cold, temp guage on dash was also dancing up and down, then started going towards hot. pulled into a parking lot and shut er down, and checked the hoses,Top rad hose was hot, while lower was cold.

the suction tube on the lid of the overflow bottle had fallen into the tank, so the rad filled it up when it started getting hot, and couldnt draw it back into the rad. I filled the rad with all of the coolant from the overflow and limped her home.
bought a new thermostat and installed it.

I burped the cooling system and went for a drive. Sitting idling at traffic lights the temp sits where it always did, but as soon as i start driving the temp on the guage lowers significantly. I've also never seen either of the fans turn on.

where can i start looking into this? I want to make sure my temp gauge is working correctly so i can keep an eye on the situation.

My gas mileage has also taking a turn for the worst, caused by the car thinking it's cold when driving, therefore running pig rich?

Thanks,

trevor

1998GsRIntegra

How many miles or in your case km's are on the current water pump?

el crapitan

i wouldn't suspect the waterpump, seeing as how he isn't overheating. the cause of his initial overheating was the suction tube of the overflow tank failing and not allowing coolant back into the system.

your cooling system is monitored by a sensor, switch and sending unit. and pcm, of course.
-the sending unit sends a voltage signal which the gauge reads.
-the temp sensor sends a voltage signal which the pcm reads.
-the fan switch closes a circuit at a specified temp and sends a signal to the relay turning on the fan.

both the sending unit and sensor can be tested by measuring their resistance with a multimeter.

if the rad fan is not coming on at all, you can test it by putting 12v power and ground to the motor. if it doesn't come on, the motor is done. if it does, try the same with the relay, and so on until you've narrowed down where the problem is

you should probably check for codes first. if there is a problem with the temp sensor, it may throw a code

fcm

Testing the ECT switch for resistance will not help, it is an on/off switch supplying a ground, [closing] to the rad fan relay when engine coolant temp. reaches about 190 degrees F.

The ECT sensor is a different story, it is a thermistor, test resistance with engine temp. cold, 50-80 degrees F and then again when engine coolant temp. is at normal running temp., the resistance should be lower.
Test the voltage of the red/white lead with ign. switch in run, [engine not running] the voltage should be approximately 5.0V.

You should also check the IAT resistance, the resistance should decrease as temp. increases.
With ign. switch in run, [engine not running] unplug the sensor and measure resistance, it should be 0.4 to 4K ohms resistance at room temp. depending on temp...
-4 = 12 ohms
32 = 5 ohms
68 = 2 ohms
104 = 1 ohm

With ign. switch in run, [engine not running] test the reference voltage lead, [red/yellow], it should be approximately 5.0V. 94

Circaskaterr

check to make sure your radiator isnt clogged it happened to my friends just take it out run water through it upside down

Van-Isle

Rad looks brand new, has fresh coolant in it, I just got the car, so not sure on mileage on the waterpump, But i dont think it's the issue.

Found out the fans do work, I had only assumed they were supposed to run constantly.

my next question is what is causing the temp gauge to drop to zero once the car is in motion? I replaced all of the lost coolant with 50/50 coolant and water.

Thermostat can only fit in the car one way correct? I just want my gauge to work so i can make sure i dont blow a head gasket.

Thanks for the help guys, Keep it coming!

Trevor

1998GsRIntegra

Depending on how talented you are usually indicates how things go back together. Lol. I would say that it is not out of the realm of relativity for a thermostat to be installed backwards but I dont think it would work very well at all. Your problem is interesting because on one hand it sounds like the thermostat is stuck open but on the other it sounds as though it isn't opening properly. I would probably be worth your time to try replacing it beacuse they are fairly inexpensive and at least half of the problem seems to be thermostat related. Good luck with it.

eaglewesman

my car was acting in a similar way (temp gauge would fluctuate randomly), so i replaced a few sensors mentioned here and it fixed my problem

el crapitan

never said to test resistance at the switch. only sending unit and sensor.

to the op, as fcm has suggested here, test the sending unit, sensor and iat. if the sending unit is reading inaccurately, you won't know if you actually are running too hot/cold so you would be just going on a wild goose chase.
you can also aim a temp gun at the sending unit as well to get a true reading.

actually. always first and foremost, check for codes