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Discussion Starter · #1 · (Edited)
I wanted to provide this write up for McLaren owners covering the replacement of a ruptured front heater hose and lower radiator hose clamps on a 2012 12c Coupe.
After pulling the car outside of the garage and letting it idle in 20 degree weather I notice an inordinate amount of steam coming from the car when I checked on it perhaps 10-20 min later. Luckily the car had not overheated but it was indeed running hotter than normal at just over the ½ point of the gauge. Looking around I could not see any specific point of origin for the coolant that was all over the ground but clearly there was quit a bit of the slimy blue coolant on the drive way and dripping from the edges of the under tray.
I pulled the car back into the garage and pulled the undertray in the back off. Careful to keep the shorter bolts separate for reinstallation on the leading edge of the tray. Perhaps the most difficult task was safely getting the car up high enough to work on with jack stands. The car is so ridged I could not simply jack it up and place it on the race Ramp as would have been my preference and driving the rear on to the ramps wasn’t an option as I was unwilling to overheat the car drestarting and driving backwards into the garage. My solution was to simply work from eith ehalf of the car at a time moving the jack between the two sides.

Once the tray was removed I was able to quickly locate the culprit . The small heater hose running from the front of the engine to the heater core connection at the bulkhead had ruptured. A close examination of the hose found that one clamp present was a spring type clamp you might find on any average car and the other clamp was an enhanced worm type clamp with embossed threads. A close examination of the hose also showed clear evidence of the worm clamp leaking for some time as there was a buildup of corrosion or effervescence at the pipe and hose connection.


Getting to the worm clamp was easy a long screwdriver did the trick however the spring clamp next to the bulkhead required specialized tool. I used a cable operated hose clamp tool to remove the spring clamp. The position of the clamp places it on the same plane if not slightly behind the bulkhead insulation making it a little tough to get a good grip on.
While I was under the car I examined the remaining hose clamps having been made aware from the forums that they are notorious for failing. As you can see from the pictures there were a few that either had become displaced or had been replaced at some point in the past and not been reassembled in the original position. I broke out the calipers and proceeded to measure all that I could easily get to or could make a reasonable guess as to the needed diameter. Now it was time to source some parts.

As the car is located in Cincinnati and usable driving days are few and far between this time of year I wanted to get the car back together to take advantage of the projected weekend weather. Plus if you were to consult my wife should would confirm that I am the most impatient human being in the world. With a call to the McLaren dealer and the subsequent FedEx anxiety out of the question I decided to source the parts on my own. I took my hose to the local parts house and found a suitable replacement. The replacement hose was a Dayco 80413, I am not sure of the application but the bend radius and diameters were perfect after trimming.




Now for the hard part, the Clamps. Being a bit of a hose clamp snob I immediately ruled out the hardware store and AutoZone varieties. I did not want sharp edges on the clamp where it interacted with the rubber and I did not want voids were worm screw interacted with the band, and lastly, I wanted a width that matched the factory clamp.
The width was an issue for two reasons
1. Since I planned on reusing other hoses I didn’t want to create a situation were the new wider clamp bridged the indentation left from the original clamp which in my mind may have created a situation of uneven pressure much like a car tire that is under inflated.

2. I’m a big dumb animal and know that if the tension on two clamps is the same but one has a smaller clamping area the actual concentrated clamping force is much greater on the thin clamp vs the wide clamp. Since the clamps leak a tighter grip must be better ( baring deformation or hose failure) . Think fishing line wrapped around your finger vs a shoestring.

Now the real problem where to find the clamp I wanted. The speed shop only had T bolt clamps with sharp edges, the Parker Store only had insanely high quality but very normally shaped worm clamps. My saving grace was a small import specialty shop called Superior Imports located in Burlington KY (my hometown). Once I explained my desire the owner quickly went to the back and brought two options. His descriptions were that I could have the Swedish one or the German one. Both were high quality and the Swedish one had a distinctive blue stamped steel worm screw holder and was very heavy duty . That clamp met all my parameters but one, it was 10-11mm’s wide. The German one was considerably lighter than the Swedish one in terms of construction but it did have the full circumference clamping, embossed worm drive, radius edges and was the proper width.
As these were universal parts I had to make do with clamps that had a range a little bigger than I would prefer but they would work. Total cost was just over 3.00 per clamp. Did I mention that I’m impatient; It is inevitable that I will be doing this job twice as I will be ordering my perfect soulmate type clamp the Oetiker 17800XX. Those clamps could hold oil and water together if arranged properly. That being said the Clamps I got to hold me over were GPM brand made in Germany 9mm width and 20mm range clamps.

Discussion of the Current Failure Mode,
I do not believe that the hose that ruptured was an original factory hose. It had makings that didn’t match the other hoses as well as the fact that its clamps were not consistent. A closer review of the hose and how it failed seemed to suggest that it was positioned in compression with a slight divot or crimp in the rubber do to haphazard nature of its install. On the engine side of the hose the end can slide several inches up the pipe as needed and on the bulkhead end of the hose there is a shoulder that keeps the hose from traveling to far onto the heater core nipple. It appeared that someone placed the hose onto the pipe and tightened the clamp and then placed the hose on the heater core end with compression forces trapped in between the two points. As the heater hose is 90 degrees it can’t be pushed away even if it’s not clamped. Lesson learned from the last guy. Tighten the heater core end first and make sure the hose is relaxed and fully engaged on the pipe end before tightening.


The observed clamps that were displaced were of factory style and are built in a way that allows consistent tension through a range of sizes. I do not know if my clamps were original or not but I can defiantly attest to the fact that the compression of the rubber leads to the loosing of the clamps. There were a few MM difference between the diameter of the “raw” hose and the diameter of the hose under the hose clamp. I do not know the precise spec on the current clamps but its clear to see that as the hose shrinks the margin of pretension on the clamps can become dangerously slim. It is my opinion that it is this shrinking that leads to many of the failures experienced by McLaren owners.

Many may observe that my preferred clamps do not offer this adjustability or pretension and your right, but I feel that the hose has at this point lost most of its compressive elasticity and represents a somewhat static size in comparison to a brand new hose. Secondly hose clamps have been tight for hundreds of year it’s only lately when combined with composite radiators and ultra-lean manufacturing that the amount of tension has become an issue. I’ll take my big dumb and tight clamps any day especially when looking at the castings and surfaces were attaching to as they are much more robust than an average KIA.

Theory on Precipitating Event Related to Failure
Many people have experienced failure either before hard running or immediately afterwards. It is my theory that the closing of thermostats in the cooling system in combination of the water pump that is not efficient at low RPM is creating an over pressure in the coolant system away from the pressure regulated fill tank. In the case of my car the engine was likely to be gaining heat relatively quickly, but the extra cold outside air and the giant radiators had a ton of thermal inertia keeping them relatively cold. I theorize that the coolant expanded in the engine fairly quickly and pushed against thermostat and was unable to flow. This coolant then couldn’t push through the moving water pump backwards to the tank(not happening) or push against the hose that already had a week spot from its improper installation and continued vibration of the engine and bulkhead. I’m not talking about crazy high pressures maybe 15-20 psi but these are pretty big pressures when compared to the size of the coolant hoses making them more likely to leak especially with compromised clamps that are even more compromised when combined with compressed hoses.

As I mentioned as you look at the pictures I will be changing the clamps again in the near future with ones of better design but frankly the ones I added will last forever they are just sloppy looking.

Tips and Tricks.
If the spring clamp on the bulkhead is factory the only way to do the job is with remote hose clamp pliers.
Line up your hose clamp worm screws to allow easy access with a tool. If you have a choice make them all face the same way.
Be mindful of the tails of the hose clamps they are a pain to work around and can cause nasty cuts to you but more importantly to the mechanic you hire to fix other stuff. A pissed off mechanic is a sloppy mechanic.
Remember the shoulder on the bulkhead fitting. Itt will prevent the hose from going on two far. Push it on until its snug but be careful put to push you clamp on to far or else is falls off the end and will take 10 minutes to fish it back out.

Don’t over tighten the clamps. Even the good ones don’t need much pressure and if you go to far and strip one DO NOT leave it on.it will fail, not maybe, or possibly but it will fail. I don’t want you spreading coolant on the track in front of me. (also don’t actually use coolant if it’s a track car)

Shortest bolts in the under tray go in the 6 spots towards the front the 4 fat ones near each jacking point and the balance are easy.

You must use a vacuum coolant bleeder or be very very patient if you do the lower radiator hoes (big ones). The tool is cheep less than 45.00 on amazon and will pay for itself in one use. If your hard headed, you can fill the system without one. Get it warm by idling. Turn off the engine and then release the fill cap quickly then cool and repeat .do this like 150 times and MOST of the air will be gone but not all. You can also adapt a medical grade penis pump to fit tightly over the filler. Pull 15-20” of vacuum and watch the coolant rise into the tube like a blue boner. Then start the car and watch it bubble and burp as you help the trapped air escape. I’m not a big fan of coolant pressure test as in the past I’ve seen overzealous testing that damages intake gaskets and water pump seals on boats. If you pressure test use 15-18psi nothing more is needed that is the literal max possible in a modern engine if all is well. Better yet use Evans water less coolant. It operates with ZERO pressure at normal temps. But be prepared to flush and prime your ass off before its over and then hope it gets along with the seals and sensors in our cars. (near future for me, ill let you know)
 

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my hose just failed yesterday you have about 5 minutes of run time before your going to have no coolant update on part number US Gates Hose #28479
 

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Here are some more pictures of the Fractured hose and the tool that makes the job a piece of cake
 

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Fine i no longer have that car but the new owner has not had any issues The hose can be sourced locally and cut to fit. The hard part is bleeding the cooling system if you do not have a suction bleeder you need to drive and let the car cool down about five times to get all the air pockets out
 

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Super awesome! Thanks for your reply :) I just finished the task last night with your write up. I used the same hose and Zerex G48 coolant. I was just worried about why the hose blow out in the first place and if there was actually more to it. Seems like a coincidence that it’s the same hose like others have blown out too. Have a great weekend and take care!
 

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I felt the hose was nothing special for the amount of heat the engine puts out . As you can see when i cut it open there was nothing special about it :(
But when it goes you got 8 minutes tops to get pulled over. and the dealer charges $1,200.00 for that hose with Labor so go out and celebrate :)
 

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I felt the hose was nothing special for the amount of heat the engine puts out . As you can see when i cut it open there was nothing special about it :(
But when it goes you got 8 minutes tops to get pulled over. and the dealer charges $1,200.00 for that hose with Labor so go out and celebrate :)
You’re right about the 8 mins 👍🏽😆 temp went from 1/2 to 3/4 yellow really quick. Good thing I was 3 mins from home. I let it cool for an hour and got some water from a house near by. Made it home with the car steaming most of the way 🤣 I spent $25 for the hose and about $75 for the coolant and a few hours. I since had to top up 2 litres from the yesterday initially 12 litres. My guess is I probably still have 6 original litres but I’ll keep checking and topping off for the next week. I love it when I have more beer money in my pocket 😜 cheers 🍻
 

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Mine burst as well in the same place, almost drained the coolant fully. Engine temp got into the yellow. I was on road and in traffic so turned off the engine during stops before I could pull over moments later. Was scary. I thought the engine was going to overheat.
 

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its like the main artery in the coolant system you have maybe 5 minutes before it will over heat the fix is not that bad but the dealer will charge you a pretty penny to do it
 
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