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Radiator gives way, starts to leak!

Shockingly it's been a month since my last post, yet the weather has been pretty fantastic, unseasonable dry for the Isle of Man, basically perfect 'Sevening' weather, so why no updates?

Sadly the car has hit a slight technical hitch. If you're a Lotus 7 club and BC forum user you'll probably be up to speed with the matter, for those that aren't I thought it time to document the situation.

Some weeks back I spotted drops of coolant appearing on my garage floor, the source seemed to align with the nearside joint between nose cone and body. At the time I convinced myself the source was probably poor fitment between the top radiator hose and the near side radiator port. The area has never been ideal as the angle of approach for the hose was by design poor. At first I addressed the matter by repeatedly re-seating and adjusting both the hose and jubilee clamp used to secure the hose. Unfortunately the problem persisted and the drops of coolant continued.

I also noticed some correlation between the volume of coolant released and how hard the car was driven, suggesting harder driving developed greater pressure and expelled more coolant, to the point I could see a small drop in the expansion tank and accumulation within the nose cone.

It was time to get serious and identify what was happening, a more detailed inspection was required.

I removed the nose once again and carefully cleaned the radiator to expel all traces of residual coolant. Using a watering can I gently poured water through the core and then over the end tanks. Each end tank was then dried with a microfibre towel while the core was gently blown dry using a car detailing dryer.

It was now time to pressurize the cooling system and identify the source of the leak. The engine was started and left to idle, permitting the temperature to rise gradually to around 80c. A small amount of throttle was then applied to lift the rpm to around 2500 rpm, and help warm the system through further. At about 100c I noticed a little steam from the radiator, but nothing more. I assumed the water to be residue from cleaning which was now evaporating. Once the temperature gauge on the dash reported 105 c the fan kicked in as expected and so I applied 3000 rpm which typically pushes the temperature down.

At this point I went and had a closer inspection of the radiator and found coolant running down the side of the core between the passenger side end tank. The stream of fluid, albeit slight appeared to start at the very top of the core immediately under the outer or external structural plate. What was most telling was the top hose and port had no traces of coolant, it was completely dry.

Caterham 7 blog radiator leak
Coolant stream running down the core from the top

From this evaluative process it was fairly conclusive, once at 105 c there was sufficient pressure in the cooling system to cause a noticeable leak in the form of a stream of coolant down the radiator core. Lower temperatures didn't seem to produce sufficient pressure for the expulsion to be as noticeable. Given engine temperatures during typical driving rarely exceed 100c averaging somewhere below 95c, it is unclear how long the issue may have been present. Having now completed sufficient running in, and subsequently been able to exploit more performance from the car I am wondering if the issue was there from the outset.

Either way, I had my results and a sound understanding of what was taking place so I reached out to Oakmere as I suspected a warranty claim was needed. The team at Oakmere were as always very helpful. They immediately offered an understanding position when it came to diagnosis and resolution from the Isle of Man, requesting only photographic evidence of the situation. Once supplied I quickly received confirmation Caterham Cars had approved a new radiator under warranty. It is probably worth commenting that I provided photographic evidence to illustrate the radiator had not suffered any form of damage, e.g. all the fins were appropriately shaped and there was no damage to the coolant vanes.

A replacement radiator was then with Oakmere within two days. Great service across

the board! To help minimize risk of courier induced damage I've recommended my in-laws collect the replacement radiator from Oakmere and drop it off when they visit later in the month. This has added a slight delay to the remediation of the fault which is fine. Yes the 7 has been off the road for slightly longer than desired, however, it's given me cause to get out and enjoy my Exige, plus do some much-needed gardening.

It isn't entirely clear whether the integrated oil cooler has been supplied as part of the replacement radiator, so the approach required to fit the replacement still needs to be confirmed. Regardless I'll post a followup blog article detailing the replacement process and how I get on. Fingers crossed it's all good!

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Simon Jones
Simon Jones
Nov 09, 2021

I have a similar age 420r that I completed around the same time as you. My second radiator is now leaking exactly as you describe. Second time around I also convinced myself for a long time that it was an issue with the hose, but I am now certain that it is coming from the core in the same place as you.

My first radiator was probably leaking from the same spot too (I again suspected the hose), but that one was replaced under warranty because of a visible leak at an external end tank weld.

All-in-all I think that Caterham had a supply problem. The question is, has this been resolved or will a new one leak? I'm thinki…

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