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Blown coolant hose - THAT one!

5K views 34 replies 10 participants last post by  Sledge4.2 
#1 ·
OK, for your enjoyment from a far, I have a new problem with Clyde. I entered the last stretch coming home from a ride a few weeks ago and looked in my rearview mirror to find steam and coolant fog trailing me. Thank God I was just coming up my neighborhood so I was able to get the car in and up on jackstands just before the needle went into the red. so no damage and no tow bill!

The coolant hose that runs between the firewall and the front of the engine on the passenger side split and shame on me for not proactively getting on thIs earlier. I have done a ton of research and talk to mechanics and bought OEM hose replacements and here is what I have found. That hose is the most problematic in Diablo‘s and will split and fail catastrophically without notice. It is also impossible to see it’s entire length and nearly impossible to get your hand in there even if your mechanic has inspected the car. that is a hose that really cannot be inspected, it can only be replaced which after reading this post I hope all of you will proactively do next time your car is in the shop. There are two hoses in the coolant system that are absolute bears to fix: this being one and the other being the heater hose that leads from the coolant tank forward along the passenger side and up behind the dashboard. That latter hose almost never fails, I am told, but the former hose that blew for me fails quite regularly. In speaking with Josh at Veloce motors here local to me he puts the car up on a lift and tries to get this particular hose out from underneath. I don’t have a lift but I have jacked my car up on stands as I normally do for changing oil. It is a pain in the rump and I will one day get a lift. That said I cannot get my elbow up between the frame member and the transmission far enough to get any leverage on that hose.

I have been distracted for the last three weeks with a large ride with my other car and some work but yesterday I started this process. First, off goes the bonnet. Do yourself a favor at this step and before you remove the bonnet nuts and washers: take a marker and draw a circle around where the washer is currently. This will go along way to helping you recenter the bonnet so that it fits properly and latches properly when you reassemble.

The last time I was in the engine I was kneeling on the two valve covers which wasn’t comfortable. I took the time yesterday to make a platform that lays on the two valve covers with carpet on both sides to protect the paint but will also protect my knees and allow me to get into the tight spaces much more comfortably. The next photo is taken from drivers side looking down in there underneath the fuel rail supply lines. Right in the center if you zoom in you can see the hose clamp that attaches to the split hose. The split is about 2 inches past the hose clamp. If you’re wondering, no one’s hand can fit down there certainly not unless you remove the fuel rails and other lines which I hope to avoid.

Lamborghini is a Latin word for “make your own tools”. It’s a 7 mm wrench on that hose clamp but there is no way to get there so this is the tool extension I had to craft. The rotation angle is very small and I’m getting maybe an 1/8th of a turn per rotation as I do not have a 7 mm internal ratchet that is thin enough to fit in this place. Once loosened you have to then pull off the hose. The hose is baked in place from heat and very hard, which is a good test for your silicon hoses if they need to be proactively replaced. They should be somewhat squishy, not hard. I don’t even bother to try pulling them off as I use a utility knife to score the end so that they will come off. Getting them back on requires heat gun and a small dab of soap.
 

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#2 ·
I was able to find at O’Reilly auto parts hose that matches the size and has internal fabric mesh reinforcement. Lamborghini OEM hose has this threaded reinforcement on the outside. Because of the heat at this part of the engine and very small area for air to circulate next to the firewall the Lamborghini OEM hose bakes the exterior thread into a brittle condition leading to failure. Apparently, in speaking with mechanics and others, this was a known condition that they remedied in the Murcialago line model by adding a small heat deflector shield on the hose at that location. I saw this OEM part but did not buy it because it was not very long, maybe 4 or 5 inches only. My solution is aftermarket auto store heat tape that reflects heat outward not inward. I will wrap the hose and secure it with metal ties before putting the hose on and do so for most of the length of the hose. This should be a permanent fix or at least until the next engine out.
The photos show the difference between OEM and auto parts store but my preference is to keep the car as much OEM as possible. The extra heat deflection wrap is a bonus.
 

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#3 ·
I was able to find at O’Reilly auto parts hose that matches the size and has internal fabric mesh reinforcement. Lamborghini OEM hose has this threaded reinforcement on the outside. Because of the heat at this part of the engine and very small area for air to circulate next to the firewall the Lamborghini OEM hose bakes the exterior thread into a brittle condition leading to failure. Apparently, in speaking with mechanics and others, this was a known condition that they remedied in the Murcialago line model by adding a small heat deflector shield on the hose at that location. I saw this OEM part but did not buy it because it was not very long, maybe 4 or 5 inches only. My solution is aftermarket auto store heat tape that reflects heat outward not inward. I will wrap the hose and secure it with metal ties before putting the hose on and do so for most of the length of the hose. This should be a permanent fix or at least until the next engine out.
 

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#7 ·
Sakura,
The hoses with the fabric on the outside are the OEMs and the ones with rubber on the outside are O'Reilly Auto. In the latter, you'll note the fabric mesh is embedded within the rubber so the heat that kills these hoses is exposed to
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o rubber, not the fabric mesh. I don't frankly know which is better but I want to keep as much OEM as possible. The one that blew for me is part number 410819370. Eurospares wants 28 UK pounds, picture from Eurospares is #3. Here, I have wrapped it in a heat shield tape to keep the heat out, and it is not pretty but this hose is very hard to see at all in the car. I am seeking function, not form on this hose.
 
#8 ·
Geno,
the hose that blew for me is connected to Eurospare part 004734347, part #10 in the 1994 parts diagram 054, and runs to a connector then runs forward to the climate control system as the heat supply hose. It is this supply hose that is supposedly the other, perhaps worse, hose to replace.
 
#13 ·
Ok, I spent tonight on what I now realize is almost, just barely doable engine-in! This was a horrific hose to get to and shreds hands and arms fully because there is just no room to get your arm in from top or from under the car, and once you do get it in there you cannot grip the hose enough to properly wiggle it on. So, here are some key learnings.
1) you must be sitting on the engine like I did on my carpet covered platform that I made in the post above. You can get a thin arm up in the car from below but you cannot see the end of the hose or the pipe it connects to. You need length longer than a for arm so your elbow must go past the small opening between frame and oil pan. Be careful as I got stuck for a few minutes! You are totally blind from below and can only feel around, not see. I chose above.
2) The hose has to go on the pipe visible in the diagram that comes off of the top of the engine by the firewall and must immediately bend down under the end of the valve cover where the cam cover cap nuts are and then immediately bend back up to connect with the heater core hose at the coolant reservoir. There is not enough room for the hose to go next to the cam cover in between the firewall, it is just too narrow, so it must drop below and then back up. For that reason there’s not enough room to get your arm in there either, so there is no leverage to get the hose onto the pipe and you cannot bend the hose around the cam cover at the same time you are pushing the hose on to the pipe as you’d need two hands for that! You also need a second set of hands or a mechanical clamp to hold it in place but there is zero room for your own hands much less another tool or another set of hands! It is a complete and total PITA.
3) recall from my post above that I bought the silicon hose from O’Reilly and the OEM hose from Lamborghini. The OEM hose is much less flexible and therefore I was having trouble getting it to make that bend to get it on the pipe. I used a small drop of dish soap and it went on the pipe but every time I would let go of the hose it would slide back off because of the back pressure of the bend and the relative inflexibility of the OEM hose itself. Here you need a second set of hands but I did not have someone else. If I did, I would have their arm up from the bottom of the car holding the hose on while I focused on getting the hose clamp in place but every time I tried to reach for the hose clamp the hose would push off due to the pressure of the bend in the hose itself. I gave up and tried the O’Reilly hose which went right on and was able to fit it in place, except for when it made the bends around the cam cover it clamped the hose shut like a hard bend in a garden hose! i.e. the silicon hose from a car part store does not have enough internal strength to make sure that the passageway stays open. Off it went again and I reached for the OEM hose, painfully.
4) at this point, I learned major lesson that I’m sure you other mechanics are already laughing at me for. In the above photo I wrapped the heat wrap all the way to the end, which is a no-no. When you wrap the heat wrap the hose cannot expand to get over the pipe nipple so I had to unwrap that portion of the heat wrap which was just another setback. Every time you pull the hose off and put it back on, which I probably did a dozen times tonight, you cut your arm even further. My arm is a complete and total wreck.
5) see the photos attached for what came off the car, in pieces. It was as dry as a desert and this hose is a ticking time bomb. Absolutely do it on any engine out but if you can get your mechanic to do it proactively for you it will save you big time. And wrap it with heat deflection tape!
6) getting the hose off with no room whatsoever required some creative thinking. I took a long piece of thin metal tube and an X-Acto knife blade and had to shred the hose until it broke its baked on seal and I was able to get it off. This took an hour!
7) I tried to take gently boiling water and dip the end of the hose in it to loosen up the rubber but I found that the dish soap trick worked just as well and was less messy.
 

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#14 ·
One last thing, getting the hose clamp back on was a bit easier than off. In my case I jammed the screw arm against the firewall so I could reach my drill gun 12” flexible extension piece down to screw it tight without having to hold the clamp. Mind you, there is only about 1/2 inch of room and it is at least 8” down below the top of the engine. Not enough room for you to hold the clamp while you tighten.
 
#15 ·
OK, my Diablo brothers, you will like this one.

While I am replacing this particular hose I figure it’s time to do the rest of the coolant hoses. Off comes the coolant reservoir last night and the associated hoses, no problem. I then start pulling the hoses for the rear return from the radiator to the water pump and the thermostat so that I can examine them and see their condition. Good news those are all in perfect shape. This in and of itself is proof that the design of the forward hose at the firewall is poor in that it is exposed to too much heat. These hoses are all the same age and the ones in the rear that have airflow around them are in perfectly good, supple, plyable condition but the one forward catastrophically blew.
I digress. When pulling off the top rear hose leading from the radiator to the thermostat, lo and behold, look what I found inside! This is some sort of rubber O-ring. It is jammed in place on the right side and cannot be removed with gentle tugging nor do I want to pull harder. My belief tonight having poured through the parts manual is I think this is the O-ring that doesn’t belong in the thermostat location but instead belongs below at the water pump location. It appears to my mind that this was an O-ring that was placed around the housing covering the thermostat but the parts manual does not call for an O-ring to be in that location. My thought is the prior mechanic years ago put the O ring around the thermostat housing instead of the water pump housing, or accidentally left an O-ring laying in there and assembled the pieces back together causing a loose O-ring inside the coolant system that thankfully got stuck and was not sucked into the water pump or tiny interior parts of the radiator. I have no other idea how that o ring made its way there. I just think the Lord that I found this before it caused greater issues.

So here is where I need help. I have not taken off the thermostat housing or the water pump in my ownership yet. does anyone know who has been in this location before if an O-ring is supposed to be at the thermostat housing? If so, maybe it wasn’t installed properly and came loose. Also, I am inclined to remove the water pump simply to determine if the O-ring is in place where it should be. Peace of mind. If I do that, is that the time to have the water pump rebuilt and belts replaced? I have no problem with the water pump and the water delivery in the coolant system other than the blown hose, but this is a question of “while I am in there”? Any comments and opinions welcome.
 

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#16 ·
is it an o-ring? or is it a lip seal? I believe the thermostats have a rubber seal around the outer edge, not an o-ring. I have seen these on some t-stats, but cant be sure they are on the diablo. Mikael would know.

if its an o-ring, thinking it must be part #6, and if that surface isn't leaking its a left over (speculation). do you have records for the car indicating water pump work? just speculation - i have not be in there or done that.

keep us posted.

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#17 ·
looking through Mikael's thread i dont see that the tstat has a circular lip seal, but someone may have stuck one in that does.

 
#18 ·
Well it turns out that Sledge is right. It was the remnants of a circular seal around the edge of the thermostat. The cross section of the seal itself was in a 'c' shape such the the seal wrapped around the outside of the thermostat's widest part and I suppose over time with vibration the edge of the thermostat cut into the seal, separating the piece as shown below. Odd. As you can see, it was just barely still attached which gives me peace of mind that there are no parts of the seal floating around in the water circuit. I’m going to clean the remnants of the gasket and clean up all of this area before reinstallation. Probably time for a new thermostat "while I'm in there".
 

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#21 ·
Memorializing what I found today. The thermostat original OEM is 66 1/2 mm diameter but it fits in a milled out female area in the housing on the engine block, at least for the 96 and beyond models, at 69 mm. The net effect is the thermostat left to right up and down is loose by several millimeters. Also, when you mate the thermostat housing on to the engine block in this location there is several millimeter gap inward that houses is the thermostat. If the thermostat has no seal around it it will vibrate left right up-and-down, but also if there is no gasket or seal in front of or behind it, it will jiggle forward and aft by several millimeters in each direction. Needless to say, the gasket needs a rubber seal around it that wraps over front and back, a cross section would look like a C. What I found out today is that seal when wrapped around the OEM thermostat is 71 mm total. The seal without the thermostat in it is exactly 68 mm and fits Inside perfectly. When you put the thermostat in it due to the interior dimension of the seal itself it stretches to 71 mm. This presented a conundrum. I spent time with my Dremel tool literally milling the OEM thermostat down to millimeters in order to have the assembly fit within the female housing on the head. this way the thermostat housing meets directly up to the head with the gasket in between and you don’t need to force it. What happened in my case was a prior mechanic jammed the thermostat in there with the seal around it and used the four bolts to seal the assembly which cut the seal and resulted in the photos above. done properly, what I did tonight, is the thermostat with seal should mate inside the female housing before you put the thermostat cover housing and gasket on it. Hope this makes sense. If you send your car off to get a new thermostat done by a mechanic I guarantee you he didn’t take these extra steps.

The first photo shows the thermostat with seal does not fit properly. The second photo shows this more clearly. The third photo shows the seal itself fits perfectly inside the female housing on the header.

as is clear to me, my car had a clutch job done with the prior owner at 10,000 miles and I suspect they replaced the thermostat with an OEM thermostat but the seal did not fit. They jammed one in there that failed. This explains why I have some new OEM hoses in the coolant system and some original OEM hoses. My belief is the one that blew forward of the engine between the firewall was original 1997.
 

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#22 ·
I have on order OEM belts and hoses because while you are in there for this project particularly at the thermostat is a perfect time to do the belts. My belts look like they’re starting to dry on the edges and get cracked which means they are ready for replacement.

I studied and studied and studied again if there was an easier way to do the belt replacement than having to disassemble further the vehicle. The answer is no. Off came the wing and then the muffler heat shield and then the aluminum top and bottom coolant pipes and tomorrow I think I will have to take the transfer bar off all in order to get visibility and 17 mm wrenches in this area in order to get the belts replaced. lambowebb.com has a great write up on replacing belts but the author assumes these things have already been removed. I don’t see a way to do the belt project while leaving the muffler heated shield in place. On top of that, the triangular bracket that the engine cover with the bull logo and firing order attaches to should be removed. If you remove that bracket you will leak coolant everywhere because it sits on the screws that hold the flange for the water pump, which is why I decided to do this belt project while my coolant system was disassembled.

The first photo shows the flange with 90° elbow in place that I simply put back finger tight in order to prevent anything from dropping into the water pump. Notice underneath the missing coolant hoses which provide access for your 17 mm spanners. The second and third photos show how tight the dimensions are between the 17 mm nuts at the power steering pump and The distance you will have to gap in order to get the belts free. I thought long and hard about removing the power steering hose in this location to make things easier. This of course would have presented its own problems with leaking power steering fluid all over the place so I opted to leave it in place and use thin 17 mm spinners.

this entire area needed cleaning so I spent time spraying it all down with multiple sprays to test. I must say of the many I tried I was equally happy with purple power and griots engine cleaner. This is messy, tedious, and good old-fashioned TLC.
 

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#23 ·
Of the many photos I’ve seen of diablo
Engines, I have noticed different hose colors and it’s driving me crazy. Note my own hoses in the center part leading to the water pump were gray but the new OEM hoses received yesterday are this color. I have seen blue, gray, black, and now orange!?!
 

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#24 ·
Now also notice the OEM hose that burst on my car, between the engine and the firewall, when I bought it a few weeks ago came out of its original OEM package in a slightly grayed, almost fuzzy condition. (First photo). My order yesterday mistakenly included the same hose again, OEM from the factory in its original packaging, (second photo) but it came back in perfectly good shape and with what looks like the heat shield on it. This leads me to believe the second photo is actually a Murciealgo hose but it’s the same part number OEM from the factory. I already replaced that hose up by the firewall and given the scars on my arm (!!) I am loathe to replace that hose again with what arrived yesterday! I suppose I now have a hose on spare which I will replace proactively again one day if I have an engine out. It is just odd that OEM from the factory can deliver two hoses in dissimilar condition.
 

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#25 ·
So that this is all memorialized in one thread, see also these notes regarding changing the belts.
 
#26 ·
My beautiful Sunday was just fine until I started smelling coolant coming out of Clyde. Remember that hose that I replaced in this thread last year? THAT one!? Well, I must not have gotten it all the way on the impossible to reach, horribly narrow, arm-slicing, Italian-curse-word-inventing, incorrectly angled metal pipe nipple in between the firewall and the front of the engine ... because it just vibrated off. I write this bored out of my gourd sitting on the side of the road waiting for the flatbed. This car is going on a one-way trip to Josh at Veloce to have this hose fixed because this time I’m going to pay him to shred his own arms. 😡

courteous reminder to every Diablo owner: have that hose fixed proactively!
 
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