Talk Morgan Forums Morgan Sports Cars Morgan Plus Four, Supersport & Plus Six (CX & CXV Generation Vehicles) Fade Away And Radiate

Basically - the rads are not fit for purpose given that a new rad was fitted last year with mileage less than 3k followed by another failure.

The Root Cause in Morgan Cars (AI)

Thermal shock occurs when a material undergoes rapid, uneven temperature fluctuations, causing different parts to expand and contract at different rates.

The Valve/Thermostat Failure:

In the CX-generation platform, early Electronic Control Unit (ECU) software poorly managed the cooling control valve.

The Shock Event:

When the cooling valve or thermostat suddenly cycled fully open, a massive rush of hot coolant or trapped steam slammed into the cold, all-aluminum radiator.Structural Stress: This rapid temperature spike forced localized sections of the aluminum to expand violently while neighboring segments remained cool, creating intense structural fatigue.

Key Impacts on the RadiatorCracked Welds and Core Failure:

The intense internal stress targets the weakest points—typically the edge of the welds where the aluminum tanks meet the cooling core

.Pressure Spikes:

The sudden arrival of steam causes mechanical and physical pressure shocks alongside the thermal shock. This expands the small, tightly sealed system beyond its limits

Chassis Aggravation:

Because traditional and modern Morgans experience significant chassis flexing and vibration, a radiator already weakened by thermal fatigue will crack much faster than one in a standard production car.

Total Coolant Loss:

Once a seam splits, coolant rapidly escapes. Because the Morgan cooling system runs at high pressure with a small header tank, a thermal-shock leak quickly leads to severe engine overheating.

The Solutions and Fixes

:ECU Software Update:

For CX-generation cars, Morgan released a mandatory dealer software update and Swirlpot retrofits. This update reprograms the cooling valve behavior to open gradually, bleeding heat into the radiator smoothly to completely eliminate the thermal shock event.

I spoke to quite a few people at Malvern before buying my CX on this issue, and they indicated,. there are many earlier cars in regular use, not just garage queens, still on their original rediators. Doesn't help those who are still experiencing problems, with their rads, but unfortunately like my clunking it maybe something \I have to live with, and may over time require an expensive fix...

Ours failed yesterday while travelling for its service, so we left it behind at the dealer and came home on the train/taxi. Almost exactly the same as clipper, fitted last year less than 3 k miles since.

I have been assured verbally by the factory that the new radiator ( No5) going back in is a different manufacturer and design. It's the same as the production cars being assembled now. So for a Plus Six almost the same as a Supersport radiator. Apparently none of the radiators from the new manufacturer have failed (yet).

The not so good news is it only has a 12 month guarantee from fitting. All the replacement radiators following the original have failed around 18 months or slightly less. So although its a new manufacturer we do not have a positive feeling about it.

We are both very deflated about it all.. we have overcome issue after issue with the car, but we are both feeling so fed up with it now, the radiators feel like a constant concern and blights each journey.. The only bright spot is that it did not fail in France 3 weeks ago when we were touring.

You are quite right to be deflated by this. It isn't acceptable. Care for loyal customers aside, it ought to be with the [DVLA?] as a recall matter. If it fails on a motorway, or anywhere congested and at speed, that could easily be a safety issue.

It can't be unsolvable, by someone with the right level of fluid dynamics theory?

Some sort of preheat by pass for coolant? Even the BL A Series had that. Or how about an electrical heating element located where the hot coolant first hits the radiator.

I still wonder what happened to all these failed radiators. And who actually carried the costs.

Or even just a thermostat that opened at a lower temperature?

The info from the MSCC chair indicated that MMC has borne the cost of the CX radiator issue (I assume both replacement parts and manhour costs to fit), and we had been told that MMC would replace any failed radiator with the 'final fix design', but this has now changed to 'two years after the last replacement' which, again, is contrary to what Dave has been told. Seems like the goalposts are constantly moving. I don't think MMC would have much of a leg to stand on if someone took them to court on the issue.

I feel really sorry for you guys, having this recurring issue, it would without question dilute understandably your confidence in the car. I hope this is the final solution to the problem. In fairness I've not seen anyone comment on much more recent cars still suffering from this issue, so hopefully it's finally fixed,.

Just thought I would through this into the mix....

the BMW B58 engine (3.0 ltr twin scroll turbo) fitted to many BWM models, 2,3,4,5 X3,X5 and Z4 plus the Toyota Supra, does not have failing radiators, yet they have the same 'thermal loading cycles?'

Mark. maybe different type of rad and airflow?

DB