High pressure radiator caps

Hard to see from the angle of the picture, but it looks like the front of the radiator is blocked by that big piece of body work to me. Those small holes drilled in the plastic are most likely not allowing enough air through the radiator.

Sorry, no help, but that looks like one gnarly machine you're building!

Is there any reason you could not adapt MX style radiator lovers to this instead of the solid plastic with holes?
I would think it would flow much more air.
See if they make a 2.0 cap.

Paw Paw

We have the cap you need in 2.0

Can I also reccomend a safety seat for that tank?

1.8 or 2.0 will yield no issues.

Paw Paw

How I would prepare for a deep sand beach race:1. good fuel/ c-12 or equivalent..2. Richer jetting..3. Radiator overflow catch can...so it can siphon coolant back into system..4. Radiator cooling fan..

Generally speaking, you're right, Paw Paw.

But, I've found that upping the cap pressure, tends to find 'tired old radiator hoses'. Just a warning to make sure , Sidecar , that you've got healthy hoses. Years ago, I got caught by something so basic - putting on a higher rated cap, and the old hoses being the weak spot. It happened in a deep , deep ravine, and pushing my 500 out was quite the misery.

I assume it's Weston you are doing - or is Le Touqette (sp?) ?

Do you always run that plastic plate directly up against the radiator like that, with only holes like I see? I've generally seen quite awesome / cool louver set ups on Sidehacks. Just getting the plastic standing off the radiator would help a bit. Run without some sort of protection, and I'll guarantee your radiator will plug up with sand, and you'll be back at being a Kettle.

You could fit a fan pretty easily behind the radiator. 12 volt car fans are pretty easy to find cheap, either new or at the wreckers and, a lttle 12volt battery could easily be found a place for in the chair / platform. A fan and a battery (constant loss, as I doubt you've a charging system - just time the batteries life with the fan on - and, you can install a simple off / on switch for when you are pinned along the beachfront) are far cheaper than a cooked engine, well, they are the sort of simple things that will, at the least, help you not waste the entry fee.

My CRE500 overheats in a second, in my preferred tight / vertiginous local single track. I tried everything - high pressure caps, various trick coolants (other than Evans types - I always wanted to be able to just fill with water if I damaged a rad / hose etc during an Enduro), machined up and welded loooooooong aluminium tube hose substitutes / inserts, a couple of catch tanks, and on and on. Fitting fans has been the only way to keep the old girl (very) happy.

Sidecar : I saw those Brits get their first (?) World Championships GP win ( at Roggenburg ) a few weeks ago. Pretty bloody cool. I subscribe to 'sidecarcrossmovies lucvanderaa' on Youtube. Latest one is from Wakes Colne - in Slomo. You in it? Now watching the 22min.29 sec.highlight package of the meet from the same bloke - only on last weekend!

Run a propylene glycol coolant instead of ehtylene. It will perform better right at the boiling point, in case you get there.

Also, do whatever you can to maximize the surface area of the aluminum; in other words, don't cover the radiators with bodywork, don't paint them, etc. Add those inline radiators if you can - anywhere along the front edge of the motorcycle would work. Here's what I'm talking about:

This is the extent to which I went with adding 'Radiator' area to my 500. After trying things like those small inserts that Falcon posted above. The LH one above is on the RH side of the bike, RH - LH. Both went backwards then forwards and up. Clearance for various parts / areas required ovalisation of sections of the tubing / trimming of fins / welds, and making of a few location brackets and component 'rub point' protection solutions - plastic / cables always win when up against aluminium - always. It added about 400ml to the total cooling system capacity, and a Lot of extra heat radiation area. Making them took many,many hours of work to fabricate. Fun - I love fabrication. They worked OK, but nothing like just the fitment of 2 fans. I have to say, the various 'trick' coolants I tried, did buggerall in the fight against boil overs, but I emphasize, my favourite local riding areas are Brutal, think Erzberg / any number of Extreme Enduros. Trials bike territory, but, I love the old warhorse in that sort of stuff- nothing can stop a 5002T from basically idling up vertical stuff, other than boil overs. And the rider hanging off it, of course......

Those things won't fit anything other than a 89 / 2001 CR500, 2002 /2003 CRE500 with an IMS tank - they are so form fitted that a std tank won't go back on over them.

Put some seal-tape/door list/ foam around the edges of the rad, that way it will force the air thru the radiator, and not around it

If you get a fan get Spal brand in 4" Pull not push type though you can get on ebay for 40 bucks, they are the ones that KTM, Honda and yamaha in there fan kits for$120 plus. I put one on my bike cause I had overheating issues when at low speeds and it worked excellent. I ran it off my stator too not off a battery like you mentioned but I'm not sure how much power your stock stator puts out so you'd have to check.

Hey Lumpy......do you suggest going to a 2.0 bar radiator cap for most Japanese bikes? I've had a few leaks on my 2015 Honda crf450 throw the radiator and was thinking that there is too much pressure and it SHOULD boil over rather than blow out the coolant system. One leak was a pinhole and the other was from a seam on the radiator. I'm interested in your opinion on this

Just wondering- when you speak of the pressure the caps rated at, i.e 1.4, 1.6, 2 bar or whatever, what is that rating exactly? Does that mean it will leak/ discharge when it goes over those figures?

Other ideas, not sure how you could implement them:-
Maybe an extra water reservior/ bottle/ container with a shut off valve, gravity fed if poss, should you start over heating and losing water? Just switch it on and off as and if required?

Also maybe could use some sort of little temp gauge to give an idea of whats going on. Don't think it has to be too cumbersome, I use these little LCD devices with a wire sensor, only about 1-2" long/ LCD display and powered by very little internal batteries. About as big as a small matchbox and weighs a few grams. Needs no wiring, other than the sensor mounting in or on the Rad, guess in it would be more accurate.
If you do get really hot, then at least you would have an idea by the gauge and pull up before blowing the engine hopefully..

EDIT : Does the pressure rating mean that when it reaches the pressure rating then cap valve/ outlet opens and the water is discharged out of hose/ outlet on side of cap. Forgot that the discharge hose is on the topside of the cap...!! That is correct isn't it?

European bikes come stock with a much higher pressure 1.8 bar cap where Japanese come stock with a 1.1 bar cap. That is the pressure the cap will release at. We reccomend running a coolant bottle so coolant can be pushed out and sucked back into the radiator so the level inside the radiator is always at the optimum level.

A higher pressure cap will find the weakest link in the system IF there is one.

Our Japanese oversized radiators come with a 1.6 and KTM/Husqvarna come with a 2.0



Moto Hose coolant bottles were the 1st system to meet AMA Racing rules for Supermoto & Pro Flat Track racing.

^^ These are the little LCD gauges I use for a few different applications. Also you could possibly mount the sensor down a small hole made in the actual discharge hose and if any water is discharged the temp display will rise dramatically and you will know you are losing coolant- or mount the sensor somewhere else?
They so small and compact you could mount maybe 2 of them- 1 in the discharge hose and another where you choose. (If you did put one in the discharge hose somehow make sure discharge hose is wide enough so the sensor doesn't block it though, where as any discharged water can still disperse).
The unit measure just 2" by 1" and cost just a few quid, sensor part is about 4mm diameter. Think you can set it to display Centigrade or Fahrenhiet.

^^ Those coolant bottles sort look quite cool! Scuse the pun... Sort of similar thing to what I was thinking when I said mounting an extra reservoir and probably quite abit neater than a homemade jobby. Small and neat looking.
Just wondering, do they too have a pressure release cap when it all starts getting abit heated?!

I'll post up some pics(hopefully tomorrow) of a really simple mod that I think will work using these little Temp gauges installed into the discharge hose, would actually be about a 10 min job or less to install and finish.
Installing the gauge once you have it should be really simple and reckon if you do start boiling/ discharging coolant then you will be able to take action before she expensively and sadly detonates/ cooks!

Also you could fairly easily regulate/ control the cooling fans, given the total loss 12v battery system, using a simple computer system fan speed regulator/ speed controller.
Got a few of them here(fan controllers) and you could lower/ or upper the speed when more/ less cooling is needed to save on the 12v battery. Would think a car fan would drain the total loss battery far too much amperage for it to last 3 hours- (depending upon battery capacity)- if you used 12v computer fans- they can kick out a surprising amount of air and prob quite gentle on how much energy they will suck from the battery. Reckon maybe 2 computer type fans would do a good job on helping to cool her or upto 4 even, depending upon 12v battery capacity and would hopefully last the distance.
Fairly simple to install also but the temp gauge thing is the easiest still.
Will post some pics up 2morrow.

Great bikes by the way- my Dad used to take me to a few sidecar MX races back in the day- remember watching those sidecar guys was something else... fearless! Off the jumps they were nuts! Ground used to shake when they landed... remember Norton Wasps and suchlike!!

... back to the MXGP!!

Put a fan on, that will go for the length of the event, and you can't go wrong . It's all about airflow through the radiators. Those tiny holes you have in that plate / protector, sure as hell don't help, but it's the 'stuck behind twats on Quads' that is bringing you undone, I reckon. I see by your "lurve note" to them, Sidecar, you are out to make friends with those 4 cornered weirdos..........

Healthy system, healthy cap, a Fan,(as discussed, just go to a Car Wreckers - any number of small car rad fans , oil cooler / transmission / intercooler fans will easily fit the 'Berg rad, cost you buggerall, and probably be water / sand proof to boot) and a nice catch tank, just in case. Look for catch tanks whilst you're at the wreckers.

No Kettle action = Healthy Engine = Healthy Wallet.

As I said, I tried all sorts of things. The best thing I ever did was fit fans. I have a toggle switch that enables me to turn them off, switch them on / of myself, or just flip the switch to thermostat. I've a HM (E-Line to the Yanks) charging system. And, I still have a catch tank on the subframe - first a Gas Gas one that wrapped around the steering head, then a KDX one, and with the PDS change over, I fitted the subframe for that, with a Yamaha WR one. When I ever get around to re painting the frame, I'll either make one to mount like the CRF450X ones, down at the downtube / cradle, or just snaffle said item from a wreckers.

My fan set up, that mounts to the radiator cages I made - I use hi flow computer fans, and have only changed them once in 9 years of use - even having drowned the bike in a few creeks / ridden in our sometimes unending dust here in OZ. How the hell the little suckers survive, I do not know, They cost about 9 bucks each. :


That weird thing with the orange silastic on it (holds on a bit of rubber in case of tank rub on the sharp edges) is a Victa Lawn Mower Vacuum Decomp. With that, even with a short Gas Gas Trials bike KS lever I use (I've non bendy knees) you can start the 500 like a PW50. Still, I do want an E Start; I reckon every kick I have to make now, is equal to one extra ride in the future ,,,,,,,,
- A very fuzzy picture of the little computer (I think that's what it is) thermostat switch - just mounted onto a plate I welded to the top of the LH radiator.

I'd love to have water proof / dust proof SPALs or the like, full time, but they are too deep with the std or IMS tank. I've made my alloy drop tanks to take SPALS, but, as I'm too often throwing the bike off cliffs at the moment, I'm not using the Alloy tank. I think I'd commit Hare Kari if I dinged it............

^^ Those fans (computer types/ PC case Fans) of Bearuno's above are the exact type fan/ setup I was on about and envisaging. They draw so very little current and are surprisingly effective. Amazing that they have lasted 9 years! They sometimes do not last that long in PC's! (some are bearing based and seize up).
Different types and qualities are available, some use slightly more juice than others but maybe have better airlfow as Bearuno says. You could also add a fan speed controller(again computer based) to increase/ decrease airflow simply.
Loving the Thermostat mod also, that is starting to go to town!

I'll stick my thermo discharge pipe mod idea up later/ pics, better do some work now...

P.s- The fans can be reversed to switch direction of airflow if needed so make sure if you mount them they are the way round where they are fanning air in the direction you want the air to flow rather than the opposite. People sometimes mount them the wrong way round for the direction of airflow they want and wonder why the fan is not effective.

If you don't have time to install as neatly as Bearuno's nice setup/ ally plates etc, they can fairly easily be cable tied - done it in many a PC when no mounting brackets were around, as long as you do not snag the blades on the ties obviously.
That is amazing how the fans have lasted 9 years! All that dust and heat- incredible.

They've been replaced once. I'm just careful when washing the bike - not hitting them directly with a hose. I think they carked it from when I didn't ride for a while, and I parked the bike near my linisher without covering it, and it ended up with a generous covering of Aluminium dust. Kills electrical equipment in my workshop, and will probably lead me to Alzheimer's in combo with my concussions....

The thermo switches cost a couple of bucks. 2 M3 threaded holes with a 24mm center to center on some 3.18 mm plate, and just weld it on. Though, not everyone has a TIG. You can easily stick a plate on, just do so with a 'wall' of glue/ liquid metal, or , I've heard, there are double sided tapes specifically made for computer heat sink attachment. The little sucker can rotate in it's base plate, and the terminals can be tweaked easily, Some pedants might go on about accurate coolant temps to the switch, but a few dollars will get you a few different temp switches to try. I ended up running a 70C one with a little roost guard in front of it. Useful things can be found in ''puter shops, even for E Tech Neanderthals like me. Well, I'm getting further into this century, as I just used my 'far smarter than me phone', to put this up.

Very cool Bearuno(no pun intended again!) Love the ideas.
- yup the ol 'puters and their parts are defo kind of useful for other stuff also given abit of imagination.....famous last words !

Right sod doing some work, this is much more fun for sure.

These are the sort of fans you maybe looking at, known as computer case fans generally :-
These are some good high quality ones but actual low airflow (very nice n' quiet for the 'puters user).


The higher output ones(more airflow) are exactly the same looking but just spin faster, consume abit more juice.You could also use a larger fan (puter based again as low consumption) than the one above-various sizes are available.

Think the larger fan though is out of some sort of server and actually spins quite slow(lower consumption/ drain).
You can also put a metal grill over them or some of them come with the grill installed (middle fans in pic have metal silver grill)- sort of may help protect the fan abit.

Consumption of these fans is about 0.12A (1.44watts) for a slower spinner - 0.25A (3watts) for a higher spinner, so reckon you could run at least 4-6 even poss) on just a 4.5Ah battery and it would last the 3 hours distance thereabouts. Think that is the case- although I'm no electronics wizkid.
A 4.5Ah sealed lead acid gel battery is small and weighs bout 2kg max, size is bout 10cm x 7cm x 10cm, so would think fairly easy to mount somewhere, maybe in the chariot somewhere?