Coolant in the expansion tank stays cold rest is Ok.

[DutchTouring]

did have a search but can't find a right one so here we go:

Changed my coolant the other day for fresh coolant.

Let it run and bled the system.

Now my problem, heater is warming up the car nicely, the engine hoses are getting warm, the temp gauge shows nice the middle so reads as normal.
Only thing is my coolant in the expansion tank (coolant reserve bottle) is even afther a few miles cold.
No overheating sings on the gauge, and hoses on the engine are all warm only the coolant in the bottle is cold.

HELP

[mrLEE30]

that is completely normal, the expansion bottle is really a kind of overflow, as the engine heats the coolant it expands and is pushed out of the cooling loop and into the bottle, when you stop the car and it cools down coolant is drawn back into the cooling system.

you have nothing to worry about

mrlee

[DutchTouring]

are you sure? All cars i had had the coolant in the tank hot afther a drive. In my E30 it stays cold even if i drive it for 20miles i can unscrew the cap on it and put my finger straight in without burning it. I thought it has to be warm because it circulates and all the coolant is warmed up.

[DutchTouring]

bump

[Brianmoooore]

There's a small amount of circulation through the small hose from the top of the radiator, but the water in the tank doesn't get particularly hot.

[s1oww]

Yep thats fine, i had the same worry with my old 325 when i changed the water. The same as you i was worried something was wrong as all my other cars heat up all the water, E30's are just odd
Its fine for it to be cold, ment to be the sign of a healthy engine.

[TRANSPORTER]

mine gets nice and warm, although when bleeding the system the other day it decide to chuck up most of the coolant out of the expansion tank, got me worried then that did, all seems to be fine now though Phew.

[DutchTouring]

so a M20B25 coolant tank needs to be cold? Well thats better then, was a little worrying the thought that it wasn't hot

[Brianmoooore]

, E30's are just odd

Not odd, just properly designed!
There should be a small amount of circulation through the header tank, via the small rubber hose from the top of the radiator.

[Martinaston]

Does it circulate though ? I've never been sure, the small hose from the top of the rad runs into the neck of the expansion tank. So when the cap is screwed down the little hole in the side is in between the two rubber seals on the cap and sits level with the little channel in it.

So does it filter down through the bottom half of the cap at all times, or is it blocked and it only releases through the top half of the cap to atmosphere when the engine overheats ?

[Brianmoooore]

The hose from the radiator goes to the small vertical pipe you can see inside the coolant bottle. The hole between the two seals leads to the rubber overflow pipe that should go out through the inner wing.

[Martinaston]

But with the cap off you can see the coolant flowing into the expansion tank from the neck ?