21 replies to this topic

[Colakurt]

I have a pretty tuned 1380cc engine and during an engine overhaul last winter I decided to upgrade the cooling system with:
* The water pump is the large plastic impeller version from minispares
* The radiator is the performance v shaped 2 core version
* 82c thermostat
* 15 bar radiator cap.

I can't see any leaks in the system yet there is always coolant under the car that looks to come from the overflow tube.

When I check the coolant levels it is always below the coolant fins which leads me to believe the engine somehow is burping more coolant up than it should.

When I refill it the level is once again lower than the fins after a drive.
The temperature seems normal on the dashboard temperature gauge, so I don't think it is overheating.

And just to make sure, I have done a compression test with 16 bar on all cylinders, I see no white smoke and the engine oil looks completely normal, so I don't suspect any internal coolant leaks.

What can I do to keep the coolant at the right level and what causes this burping when the temperature gauge says I am not overheating the system?

[timmy850]

The normal level is somewhere close to the top of the fins. As the coolant expands due to heat, any excess will come out the radiator overflow hose. If you have a standard one-way radiator cap it will only expel coolant and bring back in air. If you top it up after each drive it’ll keep sending the excess out the hose

There’s a few things you can do:
Add a catch tank to stop the leak going on the floor. You can keep an eye on the level in the catch tank and if it keeps getting higher each time, or if the engine starts overheating then you may have an issue

Add a recovery radiator cap and a recovery tank. This is a two way cap, it lets out the excess as normal, but then when the system cools it sucks coolant back in from the recovery tank

[Colakurt]

Thank you. I am aware that it is supposed to burp out the excess coolant, but from what I can read, the correct coolant level is supposed to be about an inch above the top of the fins.
In my case the level that remains is well below the top of the fins, which also makes it difficult to see what the level actually is.
I can also be afraid that I am not getting the most out of my radiator if the level is too low to exploit the full surface area.

[timmy850]

Once the coolant is being pumped through at speed it shouldn’t be a problem in regards to the surface area

You could also try starting it up from cold with the radiator cap off and see what level it is once the coolant gets hot and the thermostat opens


Do you have a heater? Have you bled the system through with the heater tap open?

[mab01uk]

Fitting an expansion tank and rad blanking cap has always worked for me in the past when having similar problems. Most other BMC/BL cars of the era like the ADO16, 1800, Maxi, etc had expansion tanks as standard and now most modern cars too. I used to fit the brass expansion tank from the 1100/1300 ADO16 (later plastic) as they were common to find in breakers yards. The BMC works Minis fitted the ADO16 expansion tank in the passengers foot well but I usually found a space under the bonnet.

 

BMC 1100 Expansion Tank

https://www.ebay.co....ASABEgICaPD_BwE

 

MGB Expansion tank
 

Edited by mab01uk, 23 October 2023 - 08:13 AM.

[Colakurt]

I do have a heater but at the moment the valve is stuck closed, even though I replaced the valve last year. From what I see I do suspect the water to exit through the overflow tube since there is coolant dripping down under the car near the tube ending. Next time I go for a drive I plan to add a bottle or something to verify that the coolant is coming from there.

 

I did try to open the cap and let the car heat up in idle. When the thermostat opened I did see coolant flowing down the channels, but not at a rate fast enough to fill the channels, also meaning air bubbles would probably get sucked down the channels and into the cooling system. The flow did increase when I reved the engine but not enough to permanently cover the fins, which is also why I suspect the level to be too low.

 

If I do add an expansion tank, is it then correctly understood that it should be located at the same level or above the overflow pipe exit so the coolant will naturally run back into the system when the engine cools down? Or where would the best location be?

[mab01uk]

If I do add an expansion tank, is it then correctly understood that it should be located at the same level or above the overflow pipe exit so the coolant will naturally run back into the system when the engine cools down? Or where would the best location be?

 

From memory on the BMC 1100/1300 the expansion tank was low down on the front panel just above the front subframe cross-member. I usually mounted mine higher up on the Minis front bulkhead wherever there was a suitable space and as said the BMC Works Rally  Minis had them down in the passenger foot well (on the wheel arch I think?) so I don't think it matters what level as the coolant will be drawn back into the radiator on cooling regardless.

 

This is a late ADO16 below with a plastic expansion tank which you can just see in the photo which is higher up than I remember the earlier brass tanks.

If I remember right the plain blanking cap was fitted on the radiator and the pressure cap was fitted on the expansion tank.

 

Edited by mab01uk, 23 October 2023 - 02:56 PM.

[timmy850]

If the heater valve is stuck you’ve likely got an air pocket in the system. I’d try and sort that out

There’s a few different tank setups
Overflow tank
Recovery tank
Expansion tank

They all need to be set up slightly different for them to work. An expansion tank is under pressure and as mentioned above has a flat cap on the radiator and the pressure cap goes on the expansion tank

[mbolt998]

Thank you. I am aware that it is supposed to burp out the excess coolant, but from what I can read, the correct coolant level is supposed to be about an inch above the top of the fins.
In my case the level that remains is well below the top of the fins, which also makes it difficult to see what the level actually is.
I can also be afraid that I am not getting the most out of my radiator if the level is too low to exploit the full surface area.

In my car the normal level is indeed an inch or so above the fins. If I can see the fins I consider that "low". I do have an "expansion bottle" (a 0.5l coke bottle) but I'm not sure whether it actually sucks anything back in from there as I have a normal radiator cap.

[JXC Mini GT]

I was experiencing a similar problem on my Mini's so I fitted expansion tanks from a Rover SD1, I fitted a plain cap to the radiator and the pressure cap to the expansion tank, the beauty of it being a clear tank is that you can check the level without removing the pressure cap.

 

 

 

[Spider]

I've always fitted an Expansion or Header Tank to my Minis, the Mokes come standard with one. I see it as a very important part of the cooling system, I don't know why the Early Minis didn't have them.

Having a Tank in what ever form, plumbed in keeps the Cooling System free of any air in it, having a small air space above the Coolant in the Radiator allows a small bit of that air to be dissolved in to the coolant and also at moderate coolant flows, bigger bubbles of air get dragged through the cooling jacket. Hardly conducive to cooling and it only leads to rusting and corrosion of the Cooling system. Fitting a head tank - like nearly every other car out there - removes all the air from the coolant.

 

[mbolt998]

I've always fitted an Expansion or Header Tank to my Minis, the Mokes come standard with one. I see it as a very important part of the cooling system, I don't know why the Early Minis didn't have them.

Having a Tank in what ever form, plumbed in keeps the Cooling System free of any air in it, having a small air space above the Coolant in the Radiator allows a small bit of that air to be dissolved in to the coolant and also at moderate coolant flows, bigger bubbles of air get dragged through the cooling jacket. Hardly conducive to cooling and it only leads to rusting and corrosion of the Cooling system. Fitting a head tank - like nearly every other car out there - removes all the air from the coolant.

 

Where does the regular radiator cap draw the air back in? I'm pretty sure I have seen water going back into my rad from my very simple coke bottle arrangement. But this doesn't seem to make much sense.

[whistler]

Do you have the correct radiator cap for that radiator. There are long and short versions with regard to the neck depth of the radiator.

Air in the isolated heater pipe could be your problem as the bottom hose end is open to water and trapped air.

[Spider]

Where does the regular radiator cap draw the air back in? I'm pretty sure I have seen water going back into my rad from my very simple coke bottle arrangement. But this doesn't seem to make much sense.

 

 

To do it with a Coke Bottle, you'd run a hose from the Radiator Overflow Outlet to the bottom of the Coke Bottle. The bottle can theoretically be placed anywhere, even lower than the Radiator, though ideally, somewhere were it's easy to see would be wisest I think.

You'd also need to change the Radiator Cap to a Recovery type Cap, they have an additional seal in them;-

 

 

 

The Cars that had the Expansion Tank fitted as standard you can find a little info on here;-

 

https://www.theminif...stralian-mokes/

 

 

 

[mbolt998]

 

Where does the regular radiator cap draw the air back in? I'm pretty sure I have seen water going back into my rad from my very simple coke bottle arrangement. But this doesn't seem to make much sense.

 

 

To do it with a Coke Bottle, you'd run a hose from the Radiator Overflow Outlet to the bottom of the Coke Bottle. The bottle can theoretically be placed anywhere, even lower than the Radiator, though ideally, somewhere were it's easy to see would be wisest I think.

You'd also need to change the Radiator Cap to a Recovery type Cap, they have an additional seal in them;-

 

 

This is my setup. No outer rubber seal but it looks like there's quite a good metal to metal contact there. It's a 0.5l coke bottle held in place with a bit of bicycle inner tube. But I'm sure I've seen it sucking a bit of water back in. Crude but seems to work a bit. Looking at it now I wonder whether it would have killed my younger self to have actually drilled a round hole in the top of that bottle rather than hacking it with penknife.

 

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