Best place to measure engine water temperature?

[A930Rocket]

What’s the best place to measure water temperature on an engine? I placed my sending unit on the radiator hose where water exits the engine.

I would think this is the hottest place to measure, unless you find somewhere at the back of the engine with less airflow. Would it be beneficial to know the radiator outlet temperature?

That said, I was seeing 210° On my autometer temp gauge driving at about 60 miles an hour. When I slowed down to 45 or 50, it cooled down to 195°. I don’t know if this was the thermostat opening and closing or what?

Edit: The aftermarket temperature gauge is making me paranoid, because the instrument cluster gauge is pointed straight up and down. On an E46, this means it’s in the normal range.

Edit 2: I realized today, my electric fan is not coming on. There is 12 V at the fan electrical connection. I hot wired the motor on the back of the fan and it spun up. The circuit board on the fan which is controlled by the DME probably toast. New fan and radiator going in next weekend. Hopefully, that fixes everything.

[Heel n Toe]

Where is the sensor for the stock guage? Maybe near there?

AFAIK, the sensor and gauge combo on my E39 work just like your E46. I've been told that the vertical position on the gauge means "fully warmed up and not overheating" and is supposed to make you feel everything's okay. Ugh.

And if it starts climbing beyond that, you better be looking at the gauge to see it. I don't know if there's a buzzer/ringer warning, but there's a warning light. Without a warning sound, it would be too easy to miss a light, IMO.

I hate the whole setup and have wondered why BMW couldn't have put a normal linear readout gauge on these cars. I've often thought I'd like to do the same thing you're doing.

I just keep an eye on all the cooling components and ask my mechanic to do the same thing... replacing stuff before it gets old enough to fail is said to be the best way to deal with the situation.

My mechanic recommended putting a 1.2 bar cap on the coolant tank to keep pressure from building up too much because of the plastic components. Trouble free since he did that. I've had the car 10 years with no cooling problems. I think he put that cap on about 8 years ago when he replaced the small rubber hoses on the right side of this drawing.


Maybe asphaltgambler or fastfredracing can offer some insight.

Multiple edits above

[pwd72s]

Similar problem with Mustangs? Maybe a relay fix?
Read this..

https://www.imboc.com/threads/burnt-fuse-block-low-speed-fan.378530/#post-3774515

[john70t]

Originally Posted by A930Rocket

Edit 2: I realized today, my electric fan is not coming on.

New fan and radiator going in next weekend. Hopefully, that fixes everything.

You can wire a manual direct feed to the rad fan for now.
Control side to a dash switch/relay/battery thick wired to motor. Fuses in both.
Use it liberally after warmup.
You will hear it and see it.

I dealt with the same problem before with an 89 Golf. Well built german engine with lucas electronics. Pressure built up until the heating evaporator radiator popped inside the cabin right side under dash. Had to bypass. Changed out three thermostats with different specs according to Chiltons/Haynes/Parts store. I never figured that one out.

Radiators can clog and fail, but change the sensor first.
And suspect the ECU, or whatever is in between, which the rad fan gets it's power from.


Turning on the A/C turns on that fan for more radiator airflow is what I read.
(This could be bad advice however.)

[A930Rocket]

I’ve replaced every piece of the cooling system except the radiator and fan about a year and a half ago. I’m not noticed any problems, because of the factory gauge and it safe buffer zone.

The factory temperature sensor is at the back of the engine, near the head/block. No way to easily access without pulling the intake etc.

I’ve read about the 1.2 bar cap and that is a good idea. With all of the plastic cooling components i.e. radiator end caps and expansion tank ready to fail.

BMW really over engineered it, as there is no relay. There is constant 12v power to the fan and the DME sends a signal to the fan controller to turn the fan on. It’s also based on the AC being on, vehicle speed, water temperature, etc. Based on all the inputs, it varies the fan speed from low to high.

I’ve read that if the fan is not working properly, it will not allow the AC to work. Driving yesterday and 90° ambient temperature, my AC was blowing 60°. Later on it started blowing out 45°.

I’m going to check the AC system today to make sure it’s fully charged and hot wire the old fan to work until the new one comes. I want to see what that does with cooling temperatures.

[masraum]

Originally Posted by A930Rocket

What’s the best place to measure water temperature on an engine? I placed my sending unit on the radiator hose where water exits the engine.

I would think this is the hottest place to measure, unless you find somewhere at the back of the engine with less airflow. Would it be beneficial to know the radiator outlet temperature?

That said, I was seeing 210° On my autometer temp gauge driving at about 60 miles an hour. When I slowed down to 45 or 50, it cooled down to 195°. I don’t know if this was the thermostat opening and closing or what?

I think on the engine would be a better place to put the temp sender, but I think it's also certain places on the engine, not just anywhere. I assume you'd need a computer model of the engine coolant to know for sure. Where is the factory gauge sender?

Edit: The aftermarket temperature gauge is making me paranoid, because the instrument cluster gauge is pointed straight up and down. On an E46, this means it’s in the normal range.

I think you'll find that most factory gauges that do NOT have numbers are not really linear gauges. I think most factory gauges today have 3 basic readings, low, regular, and high. I think you'd find that 160-220º (or something like that) all put the reading in the "normal range." I suspect you wouldn't notice a difference until the temp hit 250-270º (boiling point of coolant at 16psi). I think many/most manufacturers heavily dampened or rewired most of the coolant temp and oil press gauges years ago to eliminate issues due to people not understanding what they are seeing.
I wouldn't think that 210º would be a problem

Edit 2: I realized today, my electric fan is not coming on. There is 12 V at the fan electrical connection. I hot wired the motor on the back of the fan and it spun up. The circuit board on the fan which is controlled by the DME probably toast. New fan and radiator going in next weekend. Hopefully, that fixes everything.

Yep, dead fan is certainly not a good thing.

[masraum]

Originally Posted by Heel n Toe

AFAIK, the sensor and gauge combo on my E39 work just like your E46. I've been told that the vertical position on the gauge means "fully warmed up and not overheating" and is supposed to make you feel everything's okay. Ugh.

And if it starts climbing beyond that, you better be looking at the gauge to see it.

I hate the whole setup and have wondered why BMW couldn't have put a normal linear readout gauge on these cars. I've often thought I'd like to do the same thing you're doing.

Exactly! Most folks don't understand what they see on the gauges. Dealerships would probably be inundated with calls if temp gauges and pressure gauges read accurately and instantly. Oil pressure gauges would be the worst.

[cabmandone]

Originally Posted by A930Rocket

What’s the best place to measure water temperature on an engine? I placed my sending unit on the radiator hose where water exits the engine.

I would think this is the hottest place to measure, unless you find somewhere at the back of the engine with less airflow. Would it be beneficial to know the radiator outlet temperature?

That said, I was seeing 210° On my autometer temp gauge driving at about 60 miles an hour. When I slowed down to 45 or 50, it cooled down to 195°. I don’t know if this was the thermostat opening and closing or what?

Edit: The aftermarket temperature gauge is making me paranoid, because the instrument cluster gauge is pointed straight up and down. On an E46, this means it’s in the normal range.

Edit 2: I realized today, my electric fan is not coming on. There is 12 V at the fan electrical connection. I hot wired the motor on the back of the fan and it spun up. The circuit board on the fan which is controlled by the DME probably toast. New fan and radiator going in next weekend. Hopefully, that fixes everything.

That's really weird. I'd think at the higher speed, the air moving across the radiator would compensate for the higher speed and the slower you go, the less air moving across the radiator you'd see slightly higher temps.

I think where you put the sensor is about as good a spot as any.

[GH85Carrera]

I presume the car came with a temp switch for a light, or sender if it had a gauge. The best place to put a new sender would be as close to the factory location as possible, it not replace the factory sender. They have engineers, and some team of engineers worked on finding the perfect spot to measure the temp.

[asphaltgambler]

Optimal location is near the thermostat outlet on the front of the engine; from the top radiator hose. As for the near overheating - what vehicle / combination is it?

[A930Rocket]

Originally Posted by masraum

….Dealerships would probably be inundated with calls if temp gauges and pressure gauges read accurately and instantly. Oil pressure gauges would be the worst.

That’s what I read on the BMW forums.

Originally Posted by cabmandone

That's really weird. I'd think at the higher speed, the air moving across the radiator would compensate for the higher speed and the slower you go, the less air moving across the radiator you'd see slightly higher temps.

I think where you put the sensor is about as good a spot as any.

I was surprised by it as well. I took it for a spin today with the fan hardwired. It stayed at 210° on the autometer gauge and my OBD reader said 200°.

I was cruising about 60, slowed down to about 35 and floored it through fifth gear. It actually dropped 15° or more. I can only surmise it was pumping more coolant more quickly.

Originally Posted by GH85Carrera

I presume the car came with a temp switch for a light, or sender if it had a gauge. The best place to put a new sender would be as close to the factory location as possible, it not replace the factory sender. They have engineers, and some team of engineers worked on finding the perfect spot to measure the temp.

The factory temperature sending unit is on the back of the engine under the intake. Without taking the intake off, it’s impossible to get to it. Even if I could get to it, I don’t know if I could split it into two senders. Plus, I like torturing myself with two different readings. 😵

Originally Posted by asphaltgambler

Optimal location is near the thermostat outlet on the front of the engine; from the top radiator hose. As for the near overheating - what vehicle / combination is it?

It’s about as close as I can get to the thermostat. 2005 BMW 330ci. Stock engine.

If for some reason the new fan doesn’t work, I’m thinking about setting up a relay to power it. I don’t know the gauge of wire going to the fan, but they’re pretty big. The fuse is a 50 amp. Would a 50 amp relay work? What gauge wire and switch would I use? As this is a track oriented street car, looks don’t matter. The interior is stripped out anyway.

Schematic of the cooling system. My sending unit is located between the thermostat and the blade screw on the upper radiator hose.

[pwd72s]

Heaven forbid that a Ford and a fine car like a BMW could have the same basic problem ..but it sure sounds like it may be.

Go to the 8 minute mark for the interesting stuff...

https://www.youtube.com/watch?v=WAs6uf3VV68&ab_channel=EvanDaly

[A930Rocket]

Originally Posted by pwd72s

Heaven forbid that a Ford and a fine car like a BMW could have the same basic problem ..but it sure sounds like it may be.

Go to the 8 minute mark for the interesting stuff...

https://www.youtube.com/watch?v=WAs6uf3VV68&ab_channel=EvanDaly

Sure sounds like it after watching that video. I hope he added a grommet to all those wires going through the inner fender.

[pwd72s]

I'm hoping to figure out a preemptive strike, since I've yet to experience the problem. Hoping there's a fix without needing a dash switch. A relay that delivers the needed power to the fan while not running that much amperage power to the melting pin? Fooling the DME?

Sure wish I knew more about automotive wiring..

Yes, agree about the grommet...

[BK911]

Originally Posted by A930Rocket

What’s the best place to measure water temperature on an engine? I placed my sending unit on the radiator hose where water exits the engine.

I would think this is the hottest place to measure, unless you find somewhere at the back of the engine with less airflow. Would it be beneficial to know the radiator outlet temperature?

I had over heating issues on my 65 mustang, even with an aluminum radiator and electric fans.
Ended up putting in a temp sensor where the water exits the engine, and where it exits the radiator.
That gave me the temp difference across the radiator, so I could rule that or the fans out.
Turned out to be the electric fans did not have enough umpf at highway speeds.
More data is better than less data.

[masraum]

Originally Posted by A930Rocket

The factory temperature sending unit is on the back of the engine under the intake. Without taking the intake off, it’s impossible to get to it. Even if I could get to it, I don’t know if I could split it into two senders.

And on top of that, you wouldn't want to add any sort of T or Y fitting. The probe on the senders needs to extend into the flow of coolant. An extra fitting would likely stop both the original and new from reading correctly. With something like oil pressure, it's no big deal, but with temperature, I believe it's pretty important.

[cockerpunk]

210 isnt hot.

[GH85Carrera]

Originally Posted by BK911

I had over heating issues on my 65 mustang, even with an aluminum radiator and electric fans.
Ended up putting in a temp sensor where the water exits the engine, and where it exits the radiator.
That gave me the temp difference across the radiator, so I could rule that or the fans out.
Turned out to be the electric fans did not have enough umpf at highway speeds.
More data is better than less data.

One of my hot rod buddies hates electric fans, and always prefers to put a mechanical fan on the front of the engine. Of course he is mostly working on old 50s to 80s cars.

[A930Rocket]

Originally Posted by pwd72s

I'm hoping to figure out a preemptive strike, since I've yet to experience the problem. Hoping there's a fix without needing a dash switch. A relay that delivers the needed power to the fan while not running that much amperage power to the melting pin? Fooling the DME?

Sure wish I knew more about automotive wiring..

Yes, agree about the grommet...

Way back when, I had a 83 Mustang and I installed an electric fan with relay and temperature probe, that stuck in between the fins of the radiator. It also had an adjustable thermostat you could set the temperature to turn the fans on.

Maybe there’s something out there like that, so you don’t have to have a switch in the cockpit.

[cabmandone]

Couldn't you just drop a temp switch that closes at 185 or 190 into the coolant stream, run a low amperage circuit from the key switched power to one side of the temp switch and the other to the relay coil then power the fan from the battery with an inline fuse through the relay contacts? No additional switch needed in the cab.