H everyone, I’m just about at my wits end and can’t find a solution to my overheating issue.

I have a 1100, that has twin 1.25 SU’s, Wade 104 cam, 12G295 head in my deluxe, when ever I get on a freeway the temp climbs to over 105 degrees. It’s sucking the fun out of driving it. If I drive around town at 60~80 it seems to sit around the 90-95 mark.

To date I’ve done the following to try and fix the problem:
new radiator,
new hi flow water pump,
distributor has been recurved,
new thermostat,
new radiator cap,
new head gasket,
replaced the head with a fully reconditioned 295,
Carbies have been rebuilt and fully serviced.
I’ve replaced the electrical temperature gauge with a mechanical one to give a more accurate reading.
Replaced the coolant.

Surely the temp sitting at 105 - 107 isn’t right. However when I pull up I don’t hear it boiling. I’m not sure what the next step is or what the cause could be. Any help is appreciated.

Thanks,
James.

Beg borrow or steal an infrared thermometer and check the temperature of the thermostat housing when hot. Or the radiator top tank.
Edit:
I found my gauge electric was out a bit but the temperature fine at 180F/82C. So I added a trimpot to the sender. Cheap and cheerful solution for an OAP, it's only a club plates car.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Does your temp gauge indicate overheating at idle or just above idle? Does it overheat from cold start-up? Does it cool back to normal after overheating
Do you have a thermometer to test the actual temperature of the water in the radiator.
When the gauge indicates overheating of the coolant, is there a drop in oil pressure at the same time?
Could there be a sludge buildup in the block, heater or radiator hoses (if you didn't change them too)?


I'm sorting similar issues with my mini K at the moment. The gauge randomly rises and falls, unrelated to the engine load. But doesn't boil even when in the H zone. So far the likely cause is a partly-blocked radiator which has been chemically cleaned by a radiator shop, but it also revealed multiple holes in the tubes.
I am guessing that because I have always used plain water in the radiator but now the car is not being used as often as it was in the past, so the sludge has been able to settle and block parts of the tubes.

Thanks for the responses.
I’ve got an infrared thermometer, I’ll take a reading the next time I take it out.

I forgot to put in the first post that the engine has been flushed so there shouldn’t be any sludge inhibiting the cooling system.

Today when I took it out, it sat idling for about 15 mins and got warm 95 deg, but it cooled down pretty quickly once I got out on the road where it stabilised on about 90 deg. When it hit the freeway it climbed to about 107 deg. The temp did fall to 95 after a while after I got off the freeway. Usually at start up it settles around 85.
The oil pressure is pretty stable, sitting around 50 PSI when the engine is warm.

It’s driving me nuts and I spend my time watching the temp gauge and not enjoying the drive. I petrified that I’m going to do some serious damage.

I should say it’s now got the capillary temp gauge because one of the last ideas was that the original electric gauge may have been giving a false reading. The mechanical gauge is meant to be a lot more accurate.

Cheers,
James

Usually when overheating occurs at load (ie on the freeway) the problem is usually insufficient cooling capability.
This can mean the airflow is not cooling or the radiator is too small.
First off make sure the fan is not on backwards, then you could start playing with different fans plastic , metal etc.
A blanking tube instead of a thermostat, but do not be tempted to run without something in the housing as some back pressure is needed.
Lastly you can get better cores to go in the standard rad frame or aluminim rads are available.

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Cheers Dave.

Try a new gauge and drive it...if it is not boiling after a hard high speed run...its probably NOT overheating...

_________________
"Show me the Mini!"

Was the car running at normal temperatures at some time in the past? Has anything changed since then?
Have the changes listed in the first post been done to try to fix the overheating or has the overheating occurred since the modifications?

Have you had the car tuned professionally or better still on a dyno/ rolling road? Could CB possibly be running lean on the highway but rich around town? Could be the fan? I guess the fan belt is not slipping?
Last resort I would suggest a new radiator. Karcraft sell a good Minispares radiator which I have in my 1100 and work really well .

_________________
1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S

Have you had the car tuned professionally or better still on a dyno/ rolling road? Could CB possibly be running lean on the highway but rich around town? Could be the fan? I guess the fan belt is not slipping?
Last resort I would suggest a new radiator. Karcraft sell a good Minispares radiator which I have in my 1100 and work really well .

_________________
1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S

Thanks again everyone.
The car’s always run hot, it has just on 1500 miles on a reconditioned engine after a full restoration. The fan is on in the right direction and I’m running the original 16 blade steel fan. Is the plastic fan more efficient, if so I’ve got be that I can swap over.
I’ve had 2 electric gauges (an original grey faced Smiths, a brand new black faced Smiths) and now a brand new Smiths mechanical gauge. I’m reluctant to swap to another gauge.
The radiator is a new original styled 3 row radiator, is there a better more efficient radiator?

Thanks again,
James

If you’re running a 13lb radiator cap, it won’t actually boil until around 115C.
If you have the “standard” 3 core radiator, my understanding is that will not be good enough. Look for good alloy one, or performance 3 core.

Maybe get rid of the coolant too - unless you need anti freeze. I’m led to believe that a 50/50 mix of water and ethylene glycol (anti freeze) is two and half times more viscous than straight water (making it harder to push around), along with 15% less able to hold and transport heat.

I think you would have to believe the temp gauges are correct. Maybe an easy change is the fan? I have one of the new yellow plastic fans and my car runs cool on the motorway.

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1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S

The 3 row Minispares radiator I bought from Karcraft for our 1293 pretend S only had 8 gills/inch, regular Oz Mini radiators had 16.
Maybe they are different now (it was years ago) but it ran too hot. I changed it for a 2 core.
The 2 core one is far better at cooling but more expensive.
Edit:
My 1360 runs its original Oz Mini radiator, reconditioned and using 33% glycol coolant. 82C thermostat. It doesn't ever get too hot.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I like the metal blade fans. They might be slightly less efficient than the plastic ones, but at least the blades don’t fall off like the plastic ones tend to

Do you have a heater on the car? Is the system filled completely with no air pockets? Have you tested the thermostat opens?

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OK...if the current gauge is new "mechanical" then it is probably reading correctly...

However, how many miles have you put on the new engine? If it is still running in, then the engine may get a little hot when you switch it off...has it done plenty of highway miles? (please convert to Km/Hr if Miles offends!)...

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"Show me the Mini!"