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

AI generated specific to P6 but most likely also applies to P4

The core engine cooling architecture of the Morgan Plus Six and its donor BMW B58 engine is largely identical to BMW's cooling architecture—utilizing BMW’s advanced map-controlled electric water pump, split-cooling circuits, and ECU-managed electronic heat management module.

The differences lie entirely in the packaging, radiator fabrication, and auxiliary expansion/plumbing integration necessitated by Morgan's aluminum chassis.

Core SimilaritiesInternal Engine Flow:

Both share the B58’s split-cooling layout, which can thermally isolate the crankcase from the cylinder head during cold starts to reduce emissions and speed up warm-up.

Electronics & Thermostat:

Both rely on the stock Bosch/Siemens engine management framework to command the electronic rotary valves and variable electric water pump speeds.

Coolant Type:

Both systems are specified to run BMW HT-12 coolant mixtures.

Key Differences

Radiator Design and Durability:

BMW utilizes mass-produced, highly integrated multi-component plastic-tank radiators mapped precisely to high-volume front-end crash structures. The Morgan Plus Six utilizes bespoke, low-volume hand-fabricated radiator units packaged into the classic narrow nose cone. These custom setups have historically suffered higher rates of stress or vibration-induced cracking compared to mainstream BMW installations.

Expansion Tank and Plumbing Layout:

While a standard B58 installation in a BMW passenger car uses a tightly integrated factory expansion tank and dedicated routing paths, Morgan adapts the peripheral layout using custom header tanks, unique hose lengths, and distinct fill lines tailored to the CX-generation bonded aluminum platform.

Bleeding and Servicing:

Filling or bleeding a drained cooling system on a Morgan CX often requires strict adherence to specialized vacuum-fill procedures to avoid dangerous air pockets or hot spots in the hand-routed lines.

I think morgan have tried their best so far regarding the rad issue and been quite fair. However there has been quite a large cost implication for most of us many trips to the factory which normally means a hotel or b and b and on one occaision 2 days in one trip. If youve had three four or even five rads it will be time for a serious talk when they try to charge. Cant see it myself but then again its Morgan .Bless their overpriced cotton socks

Obviously a lot of Trad owners have been tempted to move into CX cars, I wonder if any have fallen out of love with all the bells 'n whistles and gone back to a simpler life with a Trad ?

All Morgans have problems they just come in different shapes and sizes, from the problems eg DaveW recently encountered with his GDI, the PCB's on earlier cars, all the various electrical problems and so on etc we read on this forum on a regular ulmost daily basis, the list is long.

Life as far as mechanical reliability has never been simple with any of the trad Morgans I've owned except for the pre injectors cars, and in those days it was basics like how long before the frame or chassis rebuild was next due,. despite that I still enjoy the brand, but on occasion it often comes at a price

I wouldn't swop the CX ride , the conveniences of the auto, the air conditioning, the performance and economy of the Plus Four., if anything , any of the CX Morgans will be the last Morgan I will ever own and drive.They are a massive step change for the better from the trad, and mine has been amazibgly reliable and great fun..

To be fair, the P6 has never let me down on a road trip or failed to start or required breakdown assistance. I only know the rad is leaking because the dealer tells me at the annual service.

Haven’t even lifted the bonnet this year since Ledgerwood fitted an under dash trickle charge connector at last years service ( I can hear Dave W chomping on his pipe!)

Compared to some of the ‘Mickey Mouse’ stuff that went on with the pre CX P4’s it’s been excellent - looks, ride, performance, fun factor.

My Plus Four is a 2023 car, now on 26k miles. No coolant issues at all. I think a cupfull of top up at most. Only one drip and that was from a hose joint and a quarter/half turn on the jubilee clip solved that. It prompted a check of as many clips as possible and all ok.The expansion tank cap is original and 15psi rated. There is some condensation in the clear overflow pipe that vents the expansion tank.
It's odd that some cars are having multiple failures while others are perfect. Why is my car ok? Am I tempting fate?
Several reasons and then fixes have been tried. The word is that the new rads are now ok......
Theories......
ecu with temperature sensor triggered solenoid valves instead of old school thermostats altered to reduce pressure and thermal shock.
Rad mount vibration reduced.....
Rad design and supplier changes....
Air locks in coolant.....a complex and critical process for coolant renewal that might go wrong.....
Rad cap pressure .....
I don't know if BMW cars with the same engines have rad failure problems to the same frequency as Morgans or even higher.

There may over time be an improving build quality control in place with greater empthais on the location and security of pipes and fixings,etc. as it would be one of the areas following the radiator failures I would have also focused on at Malvern., when searching for root and potential other sources for the failures. Have there been changes in the eg coolant system filling to avoid air locks.

And I do wonder in the early days of the radiator failures, as to how much the need to prevent air pockets in the coolant and any specialised procedures or equipment was available at the different dealerships when replacing the radiators under warranty.

I certainly noticed a big difference when the software update was applied to my car, done in the middle of December at Malvern, and I immediately noticed the warm up period for the heater to work dropped from 10 to about 5 minutes, indicating the water was being released more progressively and much earlier to reduce thermal shock. Very noticeable change in the draughty Morgan on cold days, much to the wife's and come to that my appreciation.



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Morgan build in mechanical challenges, not deliberately but by design. That's the essence of hand assembled. Every model has issues,but we all tolerate the issues because the benefits are greater. A friend who worships his Mx5, had the passenger window winder fail recently in Belgium. With the folding hard-hood, apparently you can't lower it when the side windows are stuck.

Anyway he was close to a Mazda dealer and they had one in stock, fitted it in a couple of hours and the cost was very reasonable. The next day, another Mx5 on the trip had the same window fail, but the dealer didn't have another drop mechanism so they had to drive on in the heat with the hood up.

So even Mx5's have weaknesses. Apparently the steel cable corrodes, and its common. Who knew?

Quality starts at the design stage. Extra effort early in design can then anticipate and modify that initial design to prevent problems.
A B48 or B58 engine in a Morgan is a significant difference to being in a bigger/heavier BMW. Didn't MMC have an approved by BMW "Morgan map" for the ecu? Add in different engine bay conditions of airflow in and out . Under bonnet temperature in a Morgan can get quote high! You can see heat haze come out of the louvres ( if you have them).
I assume MMC would log failures and investigations of them to help show causes. Component batches, procedures for assembly including checks, methods designed to prevent errors etc. Liaise with BMW to help resolve it.
the brake safety recall was based on a low incident rate. Safety critical so a very high requirement to fix. Rad failure is a lower safety issue but damaging to the brand and costly to fix. Hopefully the new rads will prove to be resilient.
High mileage testing? I am happy to volunteer my services as a test pilot/mule .👨‍🚀🐎

100% agree.. the devil is always in the detail. An American company i worked for for many years had " get it right the first time" as its motto. I do believe the last few years of Morgan production is to a higher standard than the early years of CX production, I have worked on our car over years identifying and correcting the issues caused by poor assembly and in some areas design. I am no longer in a position to redesign critical areas in our car, just do not have the connections anymore.

I am sad how the MMC responded to our mail over a genuine need for a decent guarantee regarding the latest 5th radiator. The dialogue started well, but has gone completely quiet when we asked questions about replacement radiator warranty periods over 12 months. I will see how this pans out, but presently it feels like the MMC want to draw a line in the sand ref radiator warranty claims for cars older than two years.. I have lost confidence in MMC ref the radiator saga. For some reason it makes me sad and does not sit well with us.