Morris Minor Owners Club

The recent spell of decent weather has brought on both an increase in use of our Morris Minor, but also a potentially new problem.
Stuck in traffic after a longish drive, the temperature gauge started creeping up. At around half-way between N and H, the car started running lumpy and then eventually cut out. Restarted fine and as the traffic began to move, the temperature crept back down again.
After a long drive in the heat yesterday, I've observed:

Temperature gauge holds perfectly on "N" (or just below) as long as the car is moving.
Idling, the gauge creeps up very slowly to around 1/4 of the way between N and H (after 5-10 mins).
Stop/start traffic jam, or moving very slowly, the gauge creeps up higher and the lumpy running starts.

We had a new radiator, hoses, thermostat and pump fitted in 2015 and only noticed the problem shortly after a full service this year.

Water levels are holding steady with no obvious leaks or loss of coolant. Both radiator hoses are hot when the car's up to temperature.

Any advice for what to check next?

Open the windows and turn on the heater - you may get cooked but the engine will not.
I used to have to do this when trying to traversing in my 1098cc engined Ser 2 the M6 at Preston when the traffic was at a standstill due to the widening of the M6 in and around Preston. Happy days
The temperature is exceptional at the moment and whilst the Minor is normally overcooled when stuck in stationary traffic and no air movement through the radiator other than that pulled through by the fan the engine temp is bound to rise.
Minor exported to hot countries used to be fitted with 4 fan blades for extra cooling.
You could fit the multi bladed fan off a Morris Marina.

or get an extra blade for the existing fan. Mine has had four blades since I bought it. I have no spacer / strengthener and the second blade seems to do the same job and Never had an over heating problem. However as Phil says, temperatures are exceptional at present.

They are between £9.50 and £10 inc postage on fleabay

https://www.ebay.co.uk/i/332251114776?c ... 931&crdt=0

Thank you Both. If it's likely just the (very) hot weather, I'll repeat the test next week when I'm sure our summer will be over

Great advice from the guys ( as usual...rock solid ).
I hope your garage ,who did the work in 2015 , back flushed the engine block and heater before they installed the new water pump, thermostat , radiator and hoses, etc.
A long shot but if it was early 2015 , was it filled with anti freeze and has it been renewed since then ?
The heat , here in the South East is exceptional and is testing the cooling system to the limit, roll on Friday when it's supposed to end.
Bob

As Phil says the weather is exceptionally warm at the moment so would consider this a big factor, I would also follow Bobs advice of back flushing the whole system and refilling with fresh coolant.
After a recent topic on cooling a good indication of if you have any blockages is to open the engine drain tap, if water runs out then fine but if not there will be crud in the system and a good flush will do no end of good.