Aftermarket Coolant temp sensor (after thermostat) readings. Is there a better spot?

[ewrjontan]

I have a ‘95 M3 and I placed my aftermarket coolant temp sensor in the upper radiator hose (front driver side, to the right of the thermostat if looking at the engine bay). I placed it there for simplicity knowing that it isn’t the most “ideal” spot. My car has been bled various methods (normal bleeding, raised the front, vacuum bleeding, etc) so I’m pretty sure that’s not the problem. However, the temps im seeing aren’t great. I see temps around 198-208 on hot days just cruising around; cooler days I’m looking around 198-205. At the track I’ll see my temps get close to 220 which is where I start backing off and just do cool down laps basically every other lap :/

I am running an oem 88 degree Celsius thermostat, stock clutch fan and sensor, oem water pump and z3 m coupe radiator. I have a little water wetter in there; might add more idk.

Is anyone else running a similar temp sensor setup? What are your temp readings?

Thinking of picking up a spal fan at some point but is it best to go push or pull?

Also, is there a better more accurate location? I know s52 blocks have a port in the block but the s50 does not as far as I know. I’ve seen the throttle body sensor location so I’m considering that as long as I can still keep my throttle body heater.

Thanks

[pbonsalb]

88C thermostat is 190F. The rated temp is when it begins to open, so I am not surprised to see temperatures on the radiator side being 10-20F higher. That is pretty much the hottest point in the system. The cold side of the radiator where the fan switch is located should be the coolest part. The sustained 220F at the track shows the cooling system is not keeping up, but 220F is not really that high — 50/50 coolant under pressure does not boil until about 260F.

You could try an 80C thermostat and see where you end up on the track. I suspect it will still be 220. Try adding ducting to the radiator core. Or try a larger radiator. Or a better fan.

You can put a temp sender in the head. Some heads have 3 ports and some have 2. If you are lucky there is a capped port. If not maybe you can use the throttle body line port if you plug the other end at the spaghetti hose. You may not be able to find a sender that works with your gauge and that fits the metric head threads directly. But an adapter may be available though the adapter has to fit the sender body. I’ll guess you will need a skinny sender. Some figuring required. I did it years ago but cannot recall the thread sizes.

[aeronaut]

Pbonsalb is correct, you can install a lower temp thermostat but it just delays the inevitable (it doesn't increase the cooling capacity at all).

A SPAL fan won't help with track temps, fans only help for temps while speeds are under 30mph or so.
(Replacing the whole OEM fan shebang, including the guard, with a SPAL may marginally help track temps, just because it reduces restrictions through the radiator.)

Stock (with A/C core, without hood vents), these cars are pretty sensitive to ducting. The OEM ducting works pretty well, if it's in good shape and installed correctly. If you have the Z3 radiator and no oil cooler, you've added a hole in the ducting (the Z3 radiator core is several inches shorter than the M3 radiator core). Another place mistakes are made is when installing an aftermarket underbelly. They'll need additional ducting to close up the gap between the panel and the bottom of the radiator. Ducting can easily make a 15 degree difference.

If your ducting is good, I'd install an after market full length (and maybe thicker) radiator before I'd install a SPAL fan. But it may take all of; removal of OEM mechanical and electric fan, install something like the Mish X radiator and a SPAL (assuming this is still a daily driver).

Not sure what sensor/adapter you're looking for, but BW sells this:
https://www.bimmerworld.com/Extended...T-Adapter.html
You can find other M12x1.5 to xyz adapters via searches.

[rtp-3]

Another vote for proper underpanel with baffling. On my 95 I have an aftermarket temp sender in the thermostat housing, so not that different from your upper radiator hose. Without an underpanel I would regularly see 210-220 on a hot day. With the OE Underpanel and baffle (no oil cooler) it doesn't go over 190-195.

[ewrjontan]

Very interesting. So Now that you mention the under-paneling it has me thinking. I currently run a motion motorsports under panel and "upgraded" to the Z3 M radiator since it was supposedly a slight upgrade over the stock radiator and I had a cracked upper inlet anyways.

So I remember after installing the new radiator, I felt like my temps were higher than the stock setup; track and normal conditions. I just figured that maybe it was efficient in a different way or something. I never considered the fact that the baffling would have changed due to the size of the radiator; I guess I didn't notice the difference in size. I will definitely look into it and see if I can fab something up. What is the main goal? To have all of the air coming through the center vent (and even the under-panel air) funnel to the radiator?

But realistically, are my current temps even accurate to use then in a relative sense? If I am reading 220 I probably have a few degrees more before have to truly back down?

Drove this morning on at 60 degrees and my temps stayed under 200 so that's nice haha.

[aeronaut]

Here's the ducting for the MM underpanel. It works with some of the OEM ducting that stays when you install the MM underpanel. Something like this is critical for correct ducting and lower temperature.
IMG_20220531_140146.jpg

Here's a Z3 radiator, you can see at the bottom there's room for about 1.5" more coils. That gap isn't there on the OEM M3 radiator.
(The Z3 radiator is thicker, holds the same volume of water as the M3, but has ~20% more cooling fin for the same water volume.)

Screenshot from 2022-05-31 15-48-52.png

The goal is simply to force air on the high pressure side (front) to go through the radiator, and not around. The air sees the radiator as high resistance path.

[rtp-3]

But realistically, are my current temps even accurate to use then in a relative sense? If I am reading 220 I probably have a few degrees more before have to truly back down?

Maybe, but is it worth risking a head gasket and possibly a cracked hear? Been there, done that.

I am also running an 80C thermostat and it makes no difference to the actual operating temperature on a hot (85+ F) day. Still runs up to 190-195 as that seems to be the cooling capacity of a normally operating system. On a less hot day, it makes it really difficult to get the oil temperature up to boil off condensation, which I imagine is also not terribly healthy. I'll go back to an 88c next time I change the coolant.

WRT the accuracy of the aftermarket gauge, I have the Schwaben scan tool that reads live data from the factory sensor in the head on OBD1 cars. The couple of times I checked, the temp at the thermostat housing was pretty dead on with the one in the head.

[RRSperry]

Well not for nothing, but, the OBD2 ECU and cluster get the same data from the same sensor, so I'd be surprised if they were different, shouldn't I? I've got mine in the Tsat outlet and don't go over 250F it's almost never going to hurt the engine. That isn't overheating... It's hot for sure, but it isn't hurting anything yet. So 220 if fine... It' working as it should, provided the AUX fan is also operating. Mine has never been over 210F.

[ewrjontan]

Here's the ducting for the MM underpanel. It works with some of the OEM ducting that stays when you install the MM underpanel. Something like this is critical for correct ducting and lower temperature.
IMG_20220531_140146.jpg

Here's a Z3 radiator, you can see at the bottom there's room for about 1.5" more coils. That gap isn't there on the OEM M3 radiator.
(The Z3 radiator is thicker, holds the same volume of water as the M3, but has ~20% more cooling fin for the same water volume.)

Screenshot from 2022-05-31 15-48-52.png

The goal is simply to force air on the high pressure side (front) to go through the radiator, and not around. The air sees the radiator as high resistance path.

Appreciate the info. I actually looked everything up earlier today and noticed the size difference between the two radiators and also found the baffle that I neglected to purchase years ago to save money.

I also don’t know where my oem ducting went. I don’t remember if I just tossed the whole thing or if I even had it when I installed my MM one. But yeah unfortunately I don’t have the oem side ones that fill the side gaps so I’m hoping I can source those.

Well not for nothing, but, the OBD2 ECU and cluster get the same data from the same sensor, so I'd be surprised if they were different, shouldn't I? I've got mine in the Tsat outlet and don't go over 250F it's almost never going to hurt the engine. That isn't overheating... It's hot for sure, but it isn't hurting anything yet. So 220 if fine... It' working as it should, provided the AUX fan is also operating. Mine has never been over 210F.

Dang 250!! I’m running so conservatively. When does the aux fan kick on again?

[pbonsalb]

Probably around 220 head temp. Aux fan switch is on the cold side of the radiator and that side should be about 20F cooler than the hot side thermostat housing. I think it’s 91/99C but I use a colder switch.

[ewrjontan]

Is it not possible to fit an adapter on the radiator to run both the stock fan switch as well as a sensory

[pbonsalb]

Maybe. Plastic tank. You would need a sender for a gauge and the fan switch, so some kind of adapter and tee fitting with the right threads for everything. Safest to monitor engine temp not radiator temp. Thermostat bypass is small so in winter the gauge might not show much for a while. I’d rather know engine operating temperature, preferably on the hotter side of the system, which is probably the cylinder head on an E36.

Ideally, there would be a simple way to unbuffer the stock gauge control and add a graded face to it so you would not need an aftermarket sender and gauge. After 17 years with my 99M3, I still have not seen that.

[jayjaya29]

Appreciate the info. I actually looked everything up earlier today and noticed the size difference between the two radiators and also found the baffle that I neglected to purchase years ago to save money.

I also don’t know where my oem ducting went. I don’t remember if I just tossed the whole thing or if I even had it when I installed my MM one. But yeah unfortunately I don’t have the oem side ones that fill the side gaps so I’m hoping I can source those.

You cannot run stock underpanel plastics with the MM underpanel.

For what its worth, when I switched from broken stock underpanels to the MM underpanel WITH baffle, it helped out temps significantly.

[ewrjontan]

You cannot run stock underpanel plastics with the MM underpanel.

For what its worth, when I switched from broken stock underpanels to the MM underpanel WITH baffle, it helped out temps significantly.

Yup. Took a look at the oem peices and noticed that the mm panel replaces them. I was wondering what I removed but it was probably the plastics that are right in front of the wheels. I’m definitely going to grab the radiator baffle but mm doesn’t seem to want to respond to my emails.

[M3C]

It was lot of work but I went with sensor on drain plug.

[ewrjontan]

It was lot of work but I went with sensor on drain plug.

Nice, never heard of that. Is there much room seeing as how it's right next to the exhaust manifold? What exactly made it "a lot of work"? Other than getting the bolt off, I can't imagine there's much else involved.

Do you know the size of the threads for that bolt off hand?

assuming it's #4 on this diagram?

https://www.realoem.com/bmw/enUS/sho...diagId=11_6152

[pbonsalb]

I ran one in the block drain for a while also. Bigger hole than throttle body head port so more options to fit or adapt a sender. But the head is the best place to measure coolant temp on these cars.

[jayjaya29]

Yup. Took a look at the oem peices and noticed that the mm panel replaces them. I was wondering what I removed but it was probably the plastics that are right in front of the wheels. I’m definitely going to grab the radiator baffle but mm doesn’t seem to want to respond to my emails.

MM is pretty much defunct now. So good luck on that front. If you're handy, you could fab up your own baffle using aluminum sheet.

This also exists if you're not running AC: https://kinematicspeed.com/products/radiator-duct-e36

[ewrjontan]

MM is pretty much defunct now. So good luck on that front. If you're handy, you could fab up your own baffle using aluminum sheet.

This also exists if you're not running AC: https://kinematicspeed.com/products/radiator-duct-e36

Dang, that's what I was thinking as I thought I had heard that before. I should be able to fab one up, but was willing to spend the $40-50 bucks to avoid it. Guess it's time to finally fab up my sheet metal bender

[M3C]

Nice, never heard of that. Is there much room seeing as how it's right next to the exhaust manifold? What exactly made it "a lot of work"? Other than getting the bolt off, I can't imagine there's much else involved.

Do you know the size of the threads for that bolt off hand?

assuming it's #4 on this diagram?

https://www.realoem.com/bmw/enUS/sho...diagId=11_6152

Yes it is #4, in my case because it was too short had to machine a new longer piece with tapped hole in the center so the sensor was mounted there. The O2 sensor is very close so that also had to be modified.

[The sage]

MM is pretty much defunct now. So good luck on that front. If you're handy, you could fab up your own baffle using aluminum sheet.

This also exists if you're not running AC: https://kinematicspeed.com/products/radiator-duct-e36

I went with kinematic after deleting my AC. Great product. Easy to fit and track temps are lower, not sure if the product did this or removing restrictive flow to the radiator. But i looks cool.

[ewrjontan]

I considered this but definitely would prefer to keep my ac. It’s unfortunately necessary even if I do only drive off track a few times a year.