51 replies to this topic

[JXC Mini GT]

Have you got the correct radiator pressure cap, 15lb?

 

My mini used to dump water out of the overflow, so I fitted and expansion tank which solved the problem.

 

 

[Cooperman]

I thought I had an overheating engine in my Cooper 'S'. It would go into the red within around 6 to 8 minutes after starting. I have  6-blade 'export' fan and an electric auxiliary fan and a blanking sleeve instead of a thermostat, but it still went into the 'red' very quickly. It did feel hot when I touched the top hose.

In the end I fitted a capilliary-type gauge as supplied as a kit by Mini Spares. 

On a run it was then reading 80 to 90 degrees C without the aux. fan switched on even when driven really hard (it is a 100+ bhp rally engine running with a sump guard and a row of lights across the front).

I would advise fitting a capiliary-type gauge and reading the actual temp before you start stripping the engine down further chasing a problem which may not exist. I spent a lot of time trying to sort mine when, in fact, there was no problem.

[SolarB]

 Also the water is boiling and it and spits out from the radiator. Thus the pressure in the system is building up

 

The gauge might be a bit out, but I'd trust the boiling and spitting water as an indication that this is a real problem.
 

[Quinlan minor]

Double entry

Edited by Quinlan minor, 27 August 2020 - 07:38 AM.

[Quinlan minor]

Also the water is boiling and it and spits out from the radiator. Thus the pressure in the system is building up

The gauge might be a bit out, but I'd trust the boiling and spitting water as an indication that this is a real problem.

Only if the system and the cap have been pressure tested. Otherwise boiling is no indication of overheating.

[Tornado99]

 

 Also the water is boiling and it and spits out from the radiator. Thus the pressure in the system is building up

 

The gauge might be a bit out, but I'd trust the boiling and spitting water as an indication that this is a real problem.
 

 

If the pressure cap is not correct or not holding correct pressure, then all bets are off on the boiling/spitting thing. Water boils at 100 C if at one atmosphere of pressure. Normally the cap needs to hold about 15 psi...with boil over happening above 120 C. 

[cal844]

Get a known working cap and try that.

If that doesn't solve the issue your looking at

Bad thermostat
System blockage
Or the water pump isn't working as well as it could be. (pulley the wrong size or the impeller broken up)
Inaccurate guage...

I've been there, tried all that and nothing cured the 3/4 guage readings but normal IR gun readings... Turns out my Guage is inaccurate, fuel sender level is OK though. I just live with it!

It really is quite a simple system to diagnose. The issues come when trying to get studs that have never been off in 40 years loosened successfully

Regards

Cal

[Tornado99]

Get a known working cap and try that.

If that doesn't solve the issue your looking at

Bad thermostat
System blockage
Or the water pump isn't working as well as it could be. (pulley the wrong size or the impeller broken up)
Inaccurate guage...

I've been there, tried all that and nothing cured the 3/4 guage readings but normal IR gun readings... Turns out my Guage is inaccurate, fuel sender level is OK though. I just live with it!

It really is quite a simple system to diagnose. The issues come when trying to get studs that have never been off in 40 years loosened successfully

Regards

Cal

Yup, gotta confirm real temp first using a thermometer or IR device before doing much else. As to the incorrect dash gauge, try swapping the sender unit for the other type (red versus black headed senders provide different gauge ranges...as per a recent video I saw of a guy in AUS switching from red to black sender and getting a normal reading for a high one on the black sender). 

[mullet]

Hello community.  If any of you feel this is off-topic I will create a new thread, but didn't want to create duplicates.  I don't know if oringial poster has tried what my problem is to help diagnose...?

 

So my mini (Mayfair, 1000, 1984) used to overheat in wet conditions.  I solved this with a new distributor cap & spinny arm thing inside, and new leads, thanks to advice sought here.  To note, when I bought the car, I did flush the system (very rusty water came out) and replaced fluid.

 

Now, driving in the Summer, hot days, is fine too, but only if I go over 30mph.  Any slower, the car overheats.  Gauge seems to be fine, as it was really high when I had to stop and car would not start until gauge was back in a normal zone.  I trust the gauge.  But now I don't at all trust getting stuck in motorway traffic!!!

 

Possible clue in all of this: Something I do, much to the annoyance of family, is turn on the heater inside in slow moving traffic. This certainly helps in my old Peugeot 106, definitely contributes to the cooling of the engine with extra heat lost.  In the mini, I notice that no hot air comes out until reaching 30mph.  To me, it seems there is a lack of pressure in the cooling system under a certain speed, or zero pumping action, as there's no new hot water reaching the heater inside the car (forgive me if I have not understood the mini cooling set up, but I beleive hot water is what delivers heat to the internal passenger radiator?).  Or maybe some air-flow over engine is cooling it above 30mph, and isn't anything to do with increase pressure(?), yet isn't explaining the no-hot water to internal passenger radiator, assuming i understand this correctly.

 

Those are my symptons, and before trying more extreme things, anyone have an idea based on these symptons?  I'm niaive, but a decent enough weekend mechanic once sent in the right direction.  Many thanks! :)

[Quinlan minor]

Hello community.  If any of you feel this is off-topic I will create a new thread, but didn't want to create duplicates.  I don't know if oringial poster has tried what my problem is to help diagnose...?

Now, driving in the Summer, hot days, is fine too, but only if I go over 30mph.  Any slower, the car overheats.  Gauge seems to be fine, as it was really high when I had to stop and car would not start until gauge was back in a normal zone.  I trust the gauge.  But now I don't at all trust getting stuck in motorway traffic!!!

 

Possible clue in all of this: Something I do, much to the annoyance of family, is turn on the heater inside in slow moving traffic.  In the mini, I notice that no hot air comes out until reaching 30mph.  To me, it seems there is a lack of pressure in the cooling system under a certain speed, or zero pumping action, as there's no new hot water reaching the heater inside the car (forgive me if I have not understood the mini cooling set up, but I beleive hot water is what delivers heat to the internal passenger radiator?).  Or maybe some air-flow over engine is cooling it above 30mph, and isn't anything to do with increase pressure(?), yet isn't explaining the no-hot water to internal passenger radiator, assuming i understand this correctly.

 

Those are my symptons, and before trying more extreme things, anyone have an idea based on these symptons?  I'm niaive, but a decent enough weekend mechanic once sent in the right direction.  Many thanks! :)

First, and it doesn't cost anything, check the heater circuit.

 

Disconnect flow and return pipes, from the engine, make sure heater control is turned on, connect a mains water hose to the return pipe and flush it through until the water runs clear.

Before reconnecting the hoses, elevate the hoses and fill them from a jug. Put your thumb over the end of the hoses and fit them sharpish.This reduces the chances of an air lock.

Then test to see if there is any improvement.

 

Check that the thermostat is working properly:

When starting from cold, top hose should not get hot immediately. Only once the engine is up to temperature. With your hand on the hose you shoul feel it get suddenly hot when the thermostat opens. If you have any doubt about its operation, I'd suggest replacing it. It's not expensive (though buy quality/buy once) and relatively easy to do.

 

Then test to see if there is any improvement.

 

If not, I would suspect the water pump.

 

Has a replacement been fitted? There are some poor quality, inefficient ones out there, which should be avoided at all costs!

[mullet]

Thank you Quinlan!  I will try these things.  Are your proposed solutions relating to having hot air working properly for the passenger radiator, or do you think this might be related to overheating at low speeds, too?

[Quinlan minor]

If the passenger heater matrix is sludged or air locked that might explain why it doesn’t get hot unless you are doing 30. If you do get sludge out of it, it’d be worth flushing the engine and radiator, too. It’s best to eliminate the inexpensive stuff before you throw money at it.

[mullet]

Thank you.  I will do that.  I know it's not a major part of the cooling system, but I do wonder if it makes the overall cooling that less bit efficient.  I will try.

[Quinlan minor]

Just a thought: are you sure the radiator fan is on the right way round? (Blowing from the engine bay.)

[cal844]

Just a thought: are you sure the radiator fan is on the right way round? (Blowing from the engine bay.)

Being the wrong way round will just reduce efficiency compared to what it should be

But yes I agree worth checking. The fan is marked engine side

Edited by cal844, 20 September 2020 - 04:11 PM.