420R Radiator Woes - Solutions?

[Handwheels]

My 2001 420R has got through three radiators in just over 13,000 miles - they have all leaked in the same area near the upper hose connection on the left hand side. The first one failed after 4400 miles and was replaced under warranty. This second one lasted 4480 miles (at least they failed at consistent mileages!). I then decided to try a non-Caterham rad in the hope that the cause of repeated failure was the (poor) quality of the Caterham supplied rads, so my third one was supplied by Radtec - they sell rad without the oil cooler (which I've not had a problem with) so Radtec were considerably cheaper which was a bonus.

However.. this rad failed started leaking after 4120 miles. Radtec repaired it but over the winter I've noticed it has leaked coolant while the Seven has been laid up.

I am convinced that the issue with post-2018 420s unrelated to the quality of the rads, but the negligible amount of isolation from engine/chassis vibration - although Caterham beg to differ! The mounting bobbins are so small that there can only be a few mm of rubber between the end of the stud that fixes to the chassis brackets and the threaded female sleeve that the radiator is bolted to. The rad is also rigidly held in place by the inflexible upper coolant hose and the oil hoses - the oil cooler is fixed directly to the bottom of the rad.

Pre -2018 420s had a separate oil cooler and much bigger bobbins because there was space to mount the rad  slightly further forward  because the fan was fitted to the back of the rad. From speaking to owners it appears that these earlier 420s don't have the same issues.

Caterham has accepted that they have had a lot of warranty claims on 420 rads, and as a consequence have recently changed supplier - I don't know who they have switched to. I'm not convinced that will solve the issues .

Is there anyone out there who has modified their set up and managed to get a rad to last more than 4480 miles, or have any suggestions?

Cheers, Richard

[Jonathan Kay]

There's a lot in the archives about the need to avoid stress on the radiator from the mounting points and the top hose. Have you found those threads already?

Jonathan

[Jonathan Kay]

And Radtec have suggested that the composition of the coolant is a cause. Several of us are not convinced. Have you found that discussion?

Jonathan

[Handwheels]

I hadn't spotted those discussions, so I'll do some homework :).

Thanks

[Jonathan Kay]

11 hours ago, Jonathan Kay said:

There's a lot in the archives about the need to avoid stress on the radiator from the mounting points and the top hose. Have you found those threads already?

Unfortunately it's scattered across multiple threads but I suggest starting here:

and here:

Jonathan

[Jonathan Kay]

13 hours ago, Jonathan Kay said:

And Radtec have suggested that the composition of the coolant is a cause. Several of us are not convinced. Have you found that discussion?

Same problem of multiple threads on the same subject. I suggest starting with these:

Jonathan

[Geoff Brown]

12 hours ago, Handwheels said:

My 2001 420R has got through three radiators in just over 13,000 miles - they have all leaked in the same area near the upper hose connection on the left hand side. The first one failed after 4400 miles and was replaced under warranty. This second one lasted 4480 miles (at least they failed at consistent mileages!). I then decided to try a non-Caterham rad in the hope that the cause of repeated failure was the (poor) quality of the Caterham supplied rads, so my third one was supplied by Radtec - they sell rad without the oil cooler (which I've not had a problem with) so Radtec were considerably cheaper which was a bonus.

However.. this rad failed started leaking after 4120 miles. Radtec repaired it but over the winter I've noticed it has leaked coolant while the Seven has been laid up.

I am convinced that the issue with post-2018 420s unrelated to the quality of the rads, but the negligible amount of isolation from engine/chassis vibration - although Caterham beg to differ! The mounting bobbins are so small that there can only be a few mm of rubber between the end of the stud that fixes to the chassis brackets and the threaded female sleeve that the radiator is bolted to. The rad is also rigidly held in place by the inflexible upper coolant hose and the oil hoses - the oil cooler is fixed directly to the bottom of the rad.

Pre -2018 420s had a separate oil cooler and much bigger bobbins because there was space to mount the rad  slightly further forward  because the fan was fitted to the back of the rad. From speaking to owners it appears that these earlier 420s don't have the same issues.

Caterham has accepted that they have had a lot of warranty claims on 420 rads, and as a consequence have recently changed supplier - I don't know who they have switched to. I'm not convinced that will solve the issues .

Is there anyone out there who has modified their set up and managed to get a rad to last more than 4480 miles, or have any suggestions?

Cheers, Richard

You do mean 2021 420R  as it did not exist in 2001?  When the R400 became the 420 the radiator cooling fan position was reversed so the radiator mounting configuration was changed to accommodate the implementation. IMO this change created unnecessary stress on the radiator & if one looks at the bracket arrangement it can be seen why so many failures are occurring. 

I believe that CTR Mint  found a solution by modifying the brackets to allow more radiator freedom of movement.

[Ainsley]

As I'm still building mine, can someone give me a link to "CTR Mint" so I can see what he did in regard to modifications.

Id like to modify mine now rather than after the rad leaks 🙂

[Jonathan Kay]

Various fixes to the mounts have been necessary, including turning holes into slots and packing with washers and fettling brackets. The  common aim is to make sure that there is no force applied to the body of the radiator as it is fitted and the fasteners are tightened.

The principle with the hoses is similar: to avoid mechanical loads on the stubs. I'm not sure how this is best done, but if there's a lot of axial push I'd trim them. A concertina section might help.

Jonathan

[Jonathan Kay]

12 minutes ago, Ainsley said:

As I'm still building mine, can someone give me a link to "CTR Mint" so I can see what he did in regard to modifications.

Id like to modify mine now rather than after the rad leaks

Please could you add some photos of the radiator held against the brackets.

Jonathan

[KnifeySpoony]

I and some others have changed out the top (super rigid hard rubber) rad hose for the much more flexible silicone hose from the 620R, which is available from Caterham parts. You just need a coupler, very easy install. Too soon to report on effectiveness but no issues yet on my second rad. And btw, your can get a new water rad alone from Caterham parts (ie without oil cooler) if desired. 

[Ainsley]

That, and loose bobbins may well be the answer.

[Graham Hutton]

Ainsley, my mods were combination of 3 things. Bending the aluminium brackets either side that hold the radiator mounts to ensure the front flange was absolutely parallel to the radiator. Slotting the holes in those brackets to allow the bobbins to better line up with the radiator holes. Using washers behind two of the bobbins so that all 4 bolts pinched up equally. Last thing to note is that if you go for a radtec radiator, they site further forward so the top hose needs to be a it longer. If I was building a new car now, I'd genuinely stick the caterham radiator up for sale and go straight for the radtec.

[Handwheels]

Thanks for all the comments.

For clarification it's a 2021 (not 2001!!) self-build, & I've always used the Caterham spec Motul OAT coolant. I am aware of the discussions about what is best coolant for the rad, but (as others have previously said) I've been concerned about it for the engine first.  I also used washer on rads 2 & 3 to eliminate any twisting of the rad, & I've found the fixing holes on the brackets line up perfectly with the mounting holes in the rad so not sure if I would benefit from enlarging the bracket holes.  I've not noticed a need to adjust the brackets to ensure they are parallel to the rad, but I'll double-double check that next time. When I built it I was aware of the issues some have had with the mounting bracket touching the top hose, but I've got a 2.5mm gap.

I've been concerned about the top hose being so rigid and also not being in perfect alignment of the rad coupling - so the idea of a 620R silicone hose sounds good. I've looked on Caterham Parts - is this the one (currently out of stock of course) people have used?

Thanks

[raw]

And this was my solution some years ago, using pieces of silicon hose as the bobbins. The top and bottom radiator hoses (also silicon) ensure that the rad doesn't move far anyway and the flexibility of the whole thing means that any chassis flex isn't transmitted to the radiator.

The rad in the picture has just been swapped for another Radtec due to a leak that has steadily worsened over the past few years and definitely got worse after I swapped to blue coolant last year. Blue coolant will be going back in as it seems to be a better solution for cars that are laid up over the winter. If you drive it year round then the recommended pink stuff is probably fine.

 

[Handwheels]

@raw I noticed your alternative to bobbins in an older post. Have you had to replace them since you first installed them, or have they lasted well? Sure they must be more effective at damping vibration than the 'token' ones Caterham supply

Also, what silicone hoses did you use for the top and bottom hoses? 

Cheers, Richard

[ScottR400D]

12 hours ago, Geoff Brown said:

You do mean 2021 420R  as it did not exist in 2001?  When the R400 became the 420 the radiator cooling fan position was reversed so the radiator mounting configuration was changed to accommodate the implementation. IMO this change created unnecessary stress on the radiator & if one looks at the bracket arrangement it can be seen why so many failures are occurring. 

I believe that CTR Mint  found a solution by modifying the brackets to allow more radiator freedom of movement.

Not quite right Jeff. For a few years the 420 was exactly the same as the R400 before it. CC then stopped fitting the smaller rad and separate oil cooler and fitted the ‘420 race radiator and cooler’.

There seemed no other reason for doing this than to reduce stock. The new system offered no advantage whatsoever and heralded all sort of issues. 

To compound the problem, CC couldn’t be arsed to design a new top hose but just continued to supply the hose designed for the original set up, which it fitted nicely. 

Another self inflicted wound that has been left to fester. 

[raw]

@Handwheels the silicon hose bobbins have lasted really well and I haven't had to  replace them (I think they were installed in 2013ish). The radiator hoses are Caterham silicon hoses, they've been on the car since I did the Duratec conversion in 2008/9 with no issues and they carry most of the weight of the radiator whilst the bobbins locate it in the right place. Compared to the current Caterham top hose used on the 420 the silicon hoses are much more flexible.

Andrew

 

[ScottR400D]

On the original set up which the CC hose was designed for, it fitted perfectly. Didn’t need to be that flexible.
 

 

[Jonathan Kay]

8 hours ago, raw said:

@Handwheels the silicon hose bobbins have lasted really well and I haven't had to  replace them (I think they were installed in 2013ish). The radiator hoses are Caterham silicon hoses, they've been on the car since I did the Duratec conversion in 2008/9 with no issues and they carry most of the weight of the radiator whilst the bobbins locate it in the right place. Compared to the current Caterham top hose used on the 420 the silicon hoses are much more flexible.

Thanks for sharing your solution, and I'm glad that it's working.

But I thought that the objective was to reduce mechanical load on the hose stubs or any part of the radiator other than the mounting points. 

Jonathan

[ScottR400D]

1 hour ago, Jonathan Kay said:

Thanks for sharing your solution, and I'm glad that it's working.

But I thought that the objective was to reduce mechanical load on the hose stubs or any part of the radiator other than the mounting points. 

Jonathan

Definitely. The weight of the rad should be supported on the bobbins and the hoses should be so they naturally slip onto the radiator stubs without any side load. 

[raw]

@Jonathan Kay If you look carefully at the picture you will note that the top hose actually rests on the chassis, thus supporting the top of the radiator; similarly at the bottom the same thing happens. Additional support does come from the silicon hose bobbins.

I should point out that my car was originally K series powered in an imperial chassis and when the K let go spectacularly in 2007, I installed a Raceco 210bhp Duratec but still running the K series style radiator albeit a deeper core. The metric chassis and radiators for the Duratec cars leave clearance between the top hose and the chassis rail, so the radiator bobbins do have to carry the weight of the radiator rather than utilising the hoses as well. My solution works for me but it may be worth trying a variation of it on a metric chassis.

Cheers

Andrew

[AlastairA]

I'm wondering whether using the front right towing loop as a jacking point is the cause of, or at least compounds this problem. When I used this method once, I was really concerned by the amount of torsional stress and twist on the chassis. Of course this happens mostly at the front of the car and must put huge stress on the front vertical plane (i.e. the radiator). Using the towing loop is the advice given by many but I prefer to use the lower front cruciform to get an even lift even though it's a bit of a faff to get two stands under there.

Just a thought!

[Ainsley]

Ooo, that's a good point.

[ScottR400D]

19 hours ago, raw said:

@Jonathan Kay If you look carefully at the picture you will note that the top hose actually rests on the chassis, thus supporting the top of the radiator; similarly at the bottom the same thing happens. Additional support does come from the silicon hose bobbins.

I should point out that my car was originally K series powered in an imperial chassis and when the K let go spectacularly in 2007, I installed a Raceco 210bhp Duratec but still running the K series style radiator albeit a deeper core. The metric chassis and radiators for the Duratec cars leave clearance between the top hose and the chassis rail, so the radiator bobbins do have to carry the weight of the radiator rather than utilising the hoses as well. My solution works for me but it may be worth trying a variation of it on a metric chassis.

Cheers

Andrew

I’m sorry Andrew, but that’s what I would call a lash up. It doesn’t really sound as if it works  given “The rad in the picture has just been swapped for another Radtec due to a leak that has steadily worsened over the past few years ”

There is no way that the ‘silicon hose bobbins’ offer any real support to the radiator other than fore and aft. I can’t imagine why you chose to do that rather than fit proper bobbins. Except that the way you’ve fitted the hoses would then  mean they were subject to more stress.