Garra671

Recently I had been noticing issues with my cooling system the coolant guage would go past the 0 on 180 and I wouldn’t hear fans or anything. (Already tested fans and resistors and relays).

I replaced the coolant temp sensor. Problem fixed!! Then same issue again it seems after a week of driving.

Now i currently have ordered another temp sensor just Incase I maybe did something to cause the other new one too fail, I’ll be changing it again today.

However I was doing the climate control hack to check my actual temperatures today while doing a short troubleshooting drive. And I noticed my oil temperature said 0.


Is it possible the oil temp guage is throwing off the coolant sensor? Is it possible for the oil temp sensor too go bad but not the oil level sensor? (They are 2 in 1)

THANK YOU IN ADVANCE

Macster

The climate control hack may not be a viable source of info in some cars.

The in dash coolant gauge is not really that precise of an instrument either. It response is dampened quite a bit in the middle so as long as the coolant is in the (approx.) 170F to 220F range the needle really doesn't move much. With patience and practice with an OBD2 code reader/data viewer/logger one can observe the coolant temperature in digital form and note the needle position and from this develop a "feel" of where the needle is to what the coolant temperature is but my experience is with no fine markings I was left to say with the needle on the 180 mark the temperature was (just a number now I don't recall what it actually was) 190F and every needle width more to the right was another 10F increase in coolant temperature.

In real practice I only used the coolant gauge to judge when the engine was up to temperature. If I wanted to know the actual temperature I had my handy Actron OBD2 code reader I could connect and obtain the coolant temperature. (With the Turbo I used the oil pressure gauge and now with my Hellcat I use the oil temperature gauge.)

Which brings me to: What you need is an OBD2 code reader/data viewer/logger that you can use to obtain coolant temperature from the engine controller via the OBD2 port.

You can query the engine controller for this info and view it in real time.The value you see is the value the engine controller arrives at based on the voltage level it is receiving from the sensor.

You want to see the coolant temperature, at least what the coolant temperature sensor is reporting. Based on my observation with my 2002 Boxster and my 2003 996 Turbo -- with the A/C OFF! -- the fans come on low speed when the coolant temperature reaches 212F and switch off when coolant temperature falls to 205F. If the coolant temperature continues to climb at 216F the fans switch to high speed operation and only shut off when the coolant falls to 205F. The hottest coolant temperature I ever saw with my Boxster was 226F. This was in 116F ambient heat in AZ. (The engine was unaffected by this high coolant temperature.)

If the coolant temperature reaches 212F or higher and both fans do not come on that's a problem. This happened once with my Boxster with the passenger radiator fan. I do not recall now if this was a wiring problem -- bad ballast resister -- or a bad radiator fan motor. It happened twice with my Turbo. Both times it was a bad fan motor. Once the passenger fan motor shaft snapped (!) and on the driver side while the fan was running -- I could hear it -- it was not moving nearly as much air as the other fan. Tech checked and found no fan stage errors, but did note the driver side fan motor was drawing a lot more current than the other fan motor so I had him replace the driver fan motor.

In all cases even with just fan operating there was no sign of overheating. One radiator with a properly functioning radiator fan motor can handle the heat load of the engine and even the A/C system with no problems.

But you want to be sure the temperature reported by the coolant temperature sensor reflects reality.

I have never had any reason to doubt the Boxster or Turbo coolant temperature sensor reading over the OBD2 port. But you want to be sure the coolant temperature sensor is reporting the right temperature so you need confirmation. One way is to take temperature readings from the water pump housing/T-stat housing using a hand held infra red thermometer.

You might have to get the Boxster in the air -- even if it is only by backing it up on ramps -- to be able to take temperature readings via the hand held thermometer.

As an aside, I had one time with my VW Golf TDi when the coolant temperature sensor was not working right, was reporting a cooler than actual temperature. I didn't use a hand held infra red thermometer I just observed the coolant temperature reading via the OBD2 port and noted it was not "normal", did not climb as I had become accustomed to. (Around 1 to 2 degrees F every second the engine idles after a cold start.) I do not recall what prompted me to suspect the sensor. It was not the temperature gauge reading -- the temperature gauge is really just an animated idiot light. I seem to recall it was how the engine was running. Anyhow, I took the car to the VW dealer and had the sensor replaced and all was well again.

The oil level sensor does have a temperature sensor component, a thermister located down near the bottom of the sensor tube. I do not know what the reading would be in the event of a failure. Would possibly be either -40(C) or 255(C) assuming the oil temperature sensor has a -40C bias which is what the coolant sensor has. And my reference for OBD2 PID (Parameter ID) 0x5C -- engine oil temperature -- shows min value of -40C and a max value of 215C with a scaling/bit of 1C with a -40C offset.

Garra671

@Macster I appreciate the response. I’m not too worried about the coolant temperature in the sense of a pin point accurate #. I have an OBD and can check the specific number if need be. My oil temperature sensor (in the climate hack). Says 0. I’m assuming it’s dead or on its way out, since 0 is physically impossible.

So I guess my big question is, can a Bad oil temperature sensor, effect the coolant sensors readings?

Also is it possible for the oil temperature too not work, but still have the oil level sensor work? (They are a 2 in 1 sensor)

Macster

The two sensors are separate sensors and supply the signal to the engine controller via different wiring connected to different input pins of the engine controller. The readings are processed separately and neither reading should play a role in the processing of the other reading. The engine controller might (might) use both to help it decide how it fuels the engine. If so and assuming the 0 reading was real one would think the engine controller would consider the two readings to be too far apart and flag this as a possible error and turn on the CEL.

If the 0 oil temperature reading was not a sensor failure but a problem with the engine controller there is a slim possibility that whatever is wrong at the engine controller that affects the oil temperature could also affect the coolant temperature. IOWs the engine controller is bad (or wet?) and this is affecting both sensor inputs. This is a very slim possibility but often in the Boxster OBD2 reference manual the engine controller is listed as a possible cause of the problem. But invariably it is way down the list of possible causes and I might mention below the wiring as being a cause.

The oil level sensor -- a length of bare wire in a loop that is mostly submerged in oil -- how submerged or not is what it senses -- and the oil temperature sensor -- a length of wire in a loop with the thermister located as far down in the oil lever sensor tube as possible -- are two separate sensors.

Ignoring the possibility the oil temperature sensor reading is not due to a wiring/electrical connection problem, a failure mode that could of course also affect the oil level sensor, the failure of one should not affect the other sensor. However, the oil level sensor reading might require a temperature sensor input that is used as a factor in the level the engine controller displays for the oil. This was raised as a possibility by an EE I spoke to some time ago about this when I had an oil level/temperature sensor and cut the tube apart to see how it worked. He didn't think this was the case he only mentioned it as a possibility.

I have of course noticed with my Boxster that when the engine (and thus the oil) is cold the oil level reading can be initiated and the count down timer starts at '5'. At the other end when I have shut off the engine with the engine up to full operating temperature after just a short time -- the time it takes to fill the gas tank -- I can initiate an oil level reading and the count down timer starts at '5'. The subsequent oil level reading can be a bit higher than the reading that I took when the engine and oil were cold.

But if I try to check the oil level at some temperature between "cold" and "hot" the count down timer starts at something above '5'. Considerably above '5'. Is the engine controller relying upon the oil temperature sensor reading to know how cold or hot the oil is thus at where to start the count down timer?

I don't know.

You have the chance to see if the oil temperature sensor apparently not working right has any effect on the oil level reading. All you have to do is try to take an oil level reading knowing the engine and oil are cold, as would be the case with the car sitting unused overnight. Then provided of course you can run the engine and drive the car to get the engine up to temperature shutting off the engine and then initiating an oil level reading. Without the delay from filling the gas tank the count down timer will not start at '5' if you try this reading immediately after shutting off the engine. Because I quickly became familiar with this oil level reading procedure I seldom bothered to attempt a level reading when I knew the count down timer would not start at '5'.

It might be that with the oil temperature sensor reporting '0' the oil level reading might be initiated almost immediately -- at least starting with the count timer at '5' -- no matter how brief or long a time the engine was run.

'course, if the oil temperature sensor is acting up and as best you can tell it is not a wiring or wiring connector problem at the sensor wiring harness connection why not just replace the oil level sensor/oil temperature sensor? The oil temperature could be used for other things (I vaguely recall it being used in some way regarding the operation of the VarioCam system) and with this input apparently bad this could affect the engine and its performance.