I purchased my 89 Rover Mini Automatic in 2018 and since then I have had issues with coolant boiling and radiator overflowing. The radiator has been flushed, thermostat replaced and auxillary fan fitted etc. The engine doesn't seem to overheat but the coolant boils.

My engine runs at 4000 rpm @ 100 kmh, and it has been suggested that the engine is overheating the oil and thus the coolant, causing the issues.

My mechanic has suggested converting thev4 speed auto into a 5speed manual transmission to reduce thevworkload on the engine at speed.

Would this require engineer certificate or adjustment of rego detIls?

All thoughts or advice appreciated.

Cheers


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I respectfully suggest you find a more Mini savvy mechanic...

Maybe a water pump has failed...or the engine water galleries' are gunked up...

or, blown head gasket...

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"Show me the Mini!"

Even if you swapped to manual (and the normal option is 4 speed) the cruising RPM will need to stay the same otherwise you’ll never get up hills. Minis are fine with 4000rpm all day on the highway

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Of all the ways to fix an overheating mini, I have never heard "change the gearbox"
The auto box will NOT be the problem. If your own knowledge is limited then find a decent mechanic to diagnose your cooling system
All cars will blow coolant out of the overflow pipe, that is what the overflow bottle is for. If your rad cap is stuffed the water will boil at 100c, with a new cap the pressure will up the boiling point to 130C so minimal overflow.

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Cheers Dave.

To all contributors

Your advice is well received. The radiator cap was tested and replaced yesterday.
So I will now monitor this.

I have been unable to dource a suitable radiator overflow bottle, are there any suggestions, I had been told I could use a glass bottle such as a VB bottle, that this is common on old cars. Is there any merit to this? I am currently using a repurposed plastic one but it looks terrible.

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I personally would not use a glass bottle.
This page shows the type fitted to minis
https://www.minibits.com.au/list.php?su ... &vehicle=5
They are few and far between though.
A proper expamsion or overflow tank has the pipe fed near the bottom so the cooling rad will draw water back.
The cap is also different, a pressurised cap on the rad and a non pressurised on the tank
You can buy general purpose overflow tanks from any auto spares shop.
Hope this helps.

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Cheers Dave.

Thanks Steam

I will continue the search for a proper set up.

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I am surprised yours does not have one being a 1989 rover mini, they had one on the passenger side firewall next to the wiper motor.

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Cheers Dave.

Nope it came with a hose to the road only.. my car is pre fuel injected. I thought it may be all original but seems not, do I'm not too stressed on modifying it now.

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I use a Listerene bottle as shown here with a recovery cap on the radiator. It allows the overflow coolant to be sucked back into the radiator as the engine cools.



The bottle is sort of wedged between the rad and the cross member. The hose is a tight fit in the bottle cap to stop the bottle dropping and I drilled a few extra small holes to allow the bottle to breath as it fills and empties.

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1970 Morris Mini K

Having owned an 87 rover mini that had overheating issues I feel your pain. In the end the radiator was replaced, the water pump was replaced, the timing was set correctly and the carby was properly tuned. This made a huge improvement. We never bothered to fit an overflow as the car never lost coolant after that. Take it to a proper mini specialist. It will save you $ in the long run.

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88 Rover 1.3i "Reggie"
99 Rover 1.3i “Grover”
12 Mini Cooper S "The shitter"
17 Mini Clubman JCW “Noddy”

Cheers

I have had the waterpump and thermostat replaced, the radiator flushed, the electric thermofan connected,(it wasn't prevously working and was wired backwards) and now the radiator cap tested and replaced.

The problems have greatly reduced as a result.

I have had to change mechanics as I have moved and his shop is 1hr 45mins away and across Melbourne. My new mech was introduced to me through a workmate andI is a good mechanic with mini heritage, who knows a lot about minis and my particular car.

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This may not be any problem at all but can I ask- when you say its overheating is it boiling and steaming and running badly, or is the temp gauge just reading in the red all the time?
Is it a factory gauge or aftermarket?

G'day Harley

I don't think the car is overheating so much as the coolant is boiling over. The temp guage is not staying in the red but the coolant blows out of the radiator and blew thevcap off my attempt at making a coolant overflow tank. Hopefully the new radiator cap helps.

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If you fill your radiator right up to the cap, you are actually overfilling the radiator. As the fluid in the radiator warms up, it will expand and pressure will build. When the pressure gets too high, the radiator cap will release the pressure and the coolant will leave the radiator through the overflow.

If you overflow into a sealed container, the pressure will build there and will cause the cap to burst (as you experienced).

However, none of this indicates that the car is overheating, or the coolant is boiling - this is exactly how the system is meant to work and protect itself from building up too much pressure in the cooling system.

After you've warmed the car up and let it cool, the fluid level in the radiator should be sitting at about the same height as the first row of radiator fins (or even just below). You should be able to see this if you look through the radiator cap.