When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Need Help With Coolant Temp Sensor and Sender Issues
So, a little background: Pulled 1JZ to mount CD009 trans. After install, filled radiator with coolant and started it up with the intent to top off the coolant level as the motor pulled it in. After about 2 minutes of not needing to add any coolant and seeing my elec fan kick on which is operated off of a 180deg thermostat, I went back to the cabin and noticed my AEM water temp gauge at 230 deg and my stock temp gauge through the roof. So, the AEM temp doesnt bother me too much because 230 is really not hot enough to do any damage, especially just at idle for a couple of minutes. But the temp gauge in cluster had me worried.
I fired it up yesterday from a cold start, and after a couple minutes the temp needle starts to rise beyond normal level and rapidly and I notice the engine bog down a bit and my AFR shows it richening up. Almost as if the gauge and the ECU both think that the motor is running hot. Even though after shutting it down, I went out and put my hand on the water neck and it was luke warm. So, now I am relieved that the motor didn't get as hot as I had originally thought, and am thinking that I have an issue with the temp sensor and sender.
I measured the resistance from the coolant temp sensor signal wire up at the connector all the way to the ECU connector and it was 1 ohm, so I know I have a good connection. I rang out the other pin in the connector to ground, and it had a good connection. So I'm pretty sure I have good wiring for the coolant temp sensor. For the temp sender, I unplugged it and started the car and the needle stayed all the way down, then plugged it back in and it moved. I rang out the water neck to ground and it had a good connection. I filled the water neck with coolant, thinking that maybe it would behave better if immersed in coolant, still the same thing. I measured the resistance of the coolant temp sensor at room temp and got about 1600 ohms. TSRM says that as long as there is continuity at that temp, that it's OK.
The coolant temp sensor is about 1 year old with maybe 2000 miles on it. I have a new one that I will replace it with to rule it out, and I have a new temp sender on order as well.
Does anyone have any other suggestions of things to check out while I wait for this new temp sender to come in? I've thought maybe ECU, but I didn't have these problems before I pulled the motor. Does the ECU look for anything from the auto trans, because I replaced an auto trans with the CD009?
230 is actually hot for a JZ.. not hot enough to damage it but most sit at 190-200 and it really shouldn't be above 200-210 unless you are loading it especially with a stock clutch fan and shroud. if you have the shroud off put it back on but that wont do that alone.
Since the ecu uses the 2 wire sensor and the cluster uses the 1 wire sensor, I would assume they are both working fine as the chances of both reading hot incorrectly are unlikely. the stock gauge is very sensitive, above normal temps the needle will shoot up fast and the aem reading 230 makes me think there is something wrong... so you have 2 different sensors telling you its hot.
if the waterneck feels luke warm then that could mean its not circulating the hot stuff out of the motor and that coolant is just warming up where the sensors are right behind that area. I would think the most sensible thing would be a faulty thermostat, but I think the upper hose would still be pretty hot... maybe pull the thermostat as a test and see if it still shoots up, if it doesn't well then you need a new thermostat. it could be something else though, you do have the accessory belt on right (the one that drives the waterpump)?
Thanks for the reply Ali. The 230 on the AEM was a few days ago when I first started it up.
Yesterday, the AEM didnt go beyond 80 (sorry, didn't mention that bit) by the time the needle shot up and motor bogged down. And where the needle was would indicate at least 220 degrees, yet the valve covers were lukewarm, as well as the water neck. I just don't see how both sensors could read that high given the environment that they were in. I do agree that pulling the thermostat would be a good test to eliminate that not opening as an option. But to be honest, I can't even run it long enough to even allow the motor to get to the actual thermo opening temp because it is running so rich.
Then, I also poured fresh coolant down the upper radiator pipe to immerse the sensors and it was still reading the same. It almost seems like its a grounding issue or something, even though I have ruled that out, but that's the behavior.
And yes, I do have the accessory belt on right. It is a belt for AC delete, but fits perfect around all pulleys and tension is perfect like OEM
Oh, and the thermo is 2 years old about 3000 miles
Got it all sorted. Apparently there was a jumper wire on the backside of the white combination meter plug in the passenger kick panel that fell off because it was twisted and electrical taped on... It was pin 10 on that plug which was a brown/black wire that apparently is Ignition wire for quite a few things
See pic: I just added that blue jumper wire for temporary test to see if that was the issue and it was. Tomorrow I will be soldering and shrinking that jumper in place, and also getting rid of that other nonsense splice you see in the pic... What a joke. But am VERY relieved that I didn't overheat my motor
To be honest, I didn't do anything special. I just noticed that a couple jumper wires that the previous owner put in had a loose connection, so I soldered it in and it read fine. Just have a look behind the white connector as noted and make sure that all of the wires have a solid connection and if that's all good then look at changing out the gauge sender. It's cheap.
05-20-16, 05:30 AM
Need Help With Coolant Temp Sensor and Sender Issues
