What’s the ideal thermostat housing temperature?

[twenty]

Looks like running temperature is hot topic these days. I didn’t want to add more baggage to the existing thread so here’s a new one.

I changed both the thermostat (and coolant obviously) and installed a new radiator recently after noticing that when driving on motorway the coolant temperature indicator on the dash would not reach bang on middle, but would easily when driving around in slow traffic in London. The assumption that the thermostat was stuck open.

Anyway after the changes I now noticed that the indicator doesn’t reach bang on middle anymore in city driving (haven’t been on a motorway yet) and sits a bit below the middle.

Anyway I got myself a IR thermometer and here are the results:

- 89.7c at top of thermostat housing
- 77.6c at the top radiator hose
- 48.1c at the bottom radiator hose

Seems like the thermostat temp is correct? Can anyone correlate?

Thanks!

[Brianmoooore]

If the car in question is the one at the bottom of your post, you're making a fundamental wrong assumption. Your temperature gauge needle should be in the area of the first white line on the dial, and nowhere near the middle.

[twenty]

If the car in question is the one at the bottom of your post, you're making a fundamental wrong assumption. Your temperature gauge needle should be in the area of the first white line on the dial, and nowhere near the middle.

It’s a 325i indeed. Here’s what it looks like after city driving. Are you saying that it’s overheating?

7C8C7D91-F160-45C7-BCBE-A5F3980E0325.jpeg

[Brianmoooore]

That is exactly where it should be, and stay, other than when idling for a long period, or driving slowly. In these cases it should move closer to the middle until the viscous fan coupling locks up.

[twenty]

That is exactly where it should be, and stay, other than when idling for a long period, or driving slowly. In these cases it should move closer to the middle until the viscous fan coupling locks up.

Thanks for that. So the thermostat and rad change actually did the right thing. Phew!

Out of curiosity I dug out the owners manual. It’s a bit vague in suggesting that the needle should be somewhere between blue and red.

F7FC44C8-3335-4B0E-B7F7-D77F9BA75613.jpeg

[Brianmoooore]

The handbook doesn't say where it should be, because it varies depending on engine.
316i/318i would be right in the middle.

[BristolE30]

There was literally another thread about 3 or 4 posts down about this. As Brian said 1/3 is perfect for 325i (80c thermostat). 4 pots run at half, 6 pots at 1/3.

Your all good man

[twenty]

There was literally another thread about 3 or 4 posts down about this. As Brian said 1/3 is perfect for 325i (80c thermostat). 4 pots run at half, 6 pots at 1/3.

Your all good man

That’s where it stays. I assume the temperature reading of 90 at thermostat housing is correct or was it meant to be 80 as the thermostat opens at that temperature?

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[Brianmoooore]

What's the 'quality' of that IR thermometer? The red dot is the centre of the area being measured, but the total area you are reading is cone shaped, spreading further with distance.

[twenty]

What's the 'quality' of that IR thermometer? The red dot is the centre of the area being measured, but the total area you are reading is cone shaped, spreading further with distance.

Not the best in the world. https://www.uni-trend.com/html/product/ ... T300A.html

[Blanca]

I have a similar unit and it is hopelessly low reading.

[twenty]

I have a similar unit and it is haplessly low reading.

That's bad news for me as I don't think the temp should be more than 90?

[Brianmoooore]

It doesn't matter if your IR thermometer over reads or under reads. Your temp. gauge needle is bang on where it should be, albeit not the right colour.

[twenty]

It doesn't matter if your IR thermometer over reads or under reads. Your temp. gauge needle is bang on where it should be, albeit not the right colour.

Thanks. Regarding the right colour, that’s stick photo from somewhere else. I just posted it to show where mine is. I assure you sir it’s all white!

[Brianmoooore]

And no chrome rings either?

[twenty]

And no chrome rings either?

No. The only chrome on the car is on the bumpers

[BristolE30]

There was literally another thread about 3 or 4 posts down about this. As Brian said 1/3 is perfect for 325i (80c thermostat). 4 pots run at half, 6 pots at 1/3.

Your all good man

That’s where it stays. I assume the temperature reading of 90 at thermostat housing is correct or was it meant to be 80 as the thermostat opens at that temperature?

05931809-C18D-42CF-99F6-6A69258A5930.jpeg

If your gauge is right I wouldn’t worry about it mate, just drive her