So i started a post a few days ago trying to identify whether a vacuum port has a purpose or needs capped, and that turned into a figure out the idle problem post, which after adjusting the butterfly plates ended up the car doesnt want to start now. That, however, is not the thing that makes my brain itch. After some fiddling and prodding and a fair bit of time turning then engine over with no luck I started hearing a hissing sound from one of the coolant hoses. One of the small ones. This struck me as very strange since we had very little action from this motor. The occasional piston firing but never with any authority and definitely not enough to make the coolant hot. zero time idling. So knowing that the coolant isnt hot and not a danger I loosen one of the fill caps and a considerable volume of air and coolant bursts out around this cap. The voices in my head all agree that this cannot be good news. I dont see any oil in the coolant or coolant in the oil but can someone that knows more than me tell me that I probably dont have a busted head gasket causing one or more cylinders to pressurize the cooling system. It would be fantastic to find out this bizarre circumstance was totally fine.

 

I think you'd have more symptoms if you had an actual blown head gasket.

Do you have a cooling system pressure tester? If not I think most of the auto parts stores have one you can rent. I would wait until the engine is cold, put the pressure tester on, then start the engine without pumping up the system, Watch the gauge on the pressure tester - does it spike immediately? If so then you might have something pressurizing your coolant but I wouldn't suspect a blown head gasket without at least checking that.

 

A "Block Test Kit" would detect hydrocarbons in the coolant. Simply, a dye that changes colors

Or, if you have a shop nearby with an exhaust gas analyzer, the 'sniffer' wand can used to detect hydrocarbons in the coolant

If you start the engine an immediately get churning, toiling, and bubbling in the coolant tank....it's probably compression being pumped into the cooling system.

Cheers
DD

 

Both very interesting ideas and I will look into that. The block test kits look to be pretty cheap on amazon, not sure if my local parts store rents one of those tools but that would be easy enough to check.

 

Those test tools aren't very reliable if you don't have a running engine and it sounds like you don't. I recommend you do a compression test across the board as a starting point - however - in all system failures the first thing to ask is what did you change last. Induction system leaks can be fickle especially on the V12 - there are so many places where air can get in and the aren't all in the engine bay but an air leak would need to be pretty severe to prevent running - got spark, got timing, got fuel pressure, got injector triggering, got air - if yes to all then it should run.

Messing with throttle butterfly's shouldn't be the issue but it is unwise to disregard things - the number of issues where I've said 'it cannot be that' and it was, or something stupid that I totally disregarded have been major life lessons.

If you can get it running one of the best tools to confirm a vacuum leak is well aimed brake clean.

But if you want to test for combustion gases you need to generate some .... only things that can generate pressure within an engine are heat and pistons - nothing else but I don't think I've ever encountered a failure so severe in a head gasket that even turning on the starter can generate pressure.

Rent an inexpensive tool ?? - the tool isn't what does the gas test it is the fluid you put into it and you don't need much so you would end up with fluid and no tool - why you would want to rent such a tool intrigues me - can never have too many tools

 

Far as borrowing a tool from a local parts store I was talking about the cooling system pressure tester that someone else had mentioned. The fluid tester I can find for like 20 bucks, so I'd just buy that but the other one is more like 65 and borrowing from the local parts stores is essentially free so I tend to borrow tools I dont have a regular use for rather than buy them.

I also use brake clean to find vacuum leaks or something similar, and I cant find any. I plan to eventually replace all the vacuum lines just because they're old but I've replaced all the ones that were obviously fail and haven't been able to track down any new leaks. Where besides the engine bay could there be a leak? I rebuilt the transmission recently and replaced the vacuum line going down to it.

As far as what I changed last, I did a few things all around the same time. Replaced the water pump, took out some unnecessary emissions stuff and capped any abandoned vacuum lines for that, changed out the belt driven fan for an electric, also replaced the top hat seals on both water rails and cleaned up the AAV. A little while before all that i built a new injector harness. In the last day or so I have been able to make it run. The idle is a little high but I still plan to look more at this issue as I work on other things just because its kinda weird. I've never had a cooling system pressurize like that before so even if its not actually a problem I'd like to figure out why it does that. After I got it to run and let it idle for a bit to come up to temp to make sure my new fan would work like its suppose to, I didnt hear any more hissing which you'd think I would if I was experiencing the problem I thought I could be. While it idled I also noticed a significant oil leak from the front pan that will be no fun to sort out lol

 

If you have it running then the gas test should be OK though I'm not sure where I'd conduct it - I'd say the filler but you'd need to pinch off the bleed. Borrowing for free - hell yeh I'd go for some of that too - I have shelves full of stuff I've used once - glow plug and injector tools, cam setting and locking tools, locking bars for specific cranks for doing end bolts - I could go on. I'm not sure where you would run the pressure test - expansion tank or filler neck because of the expansion tanks location

If you have it running satisfy yourself on the head gasket or it will fester and grow in your mind and cloud the issue, I have encountered the 'volcanic' eruption in cars seemingly cold caused by air locks thogh not on the V12 - basically localised heating boils and explodes out.

If it is the pan you need to seal this isn't so bad - if it is the plate above it that job is a bear and requires subframe removal - you may be able to get it by pivoting the subframe down on the front mounts but there's still a whole bunch of stuff you need to disconnect - which once disconnected leaves only the front mounts so may as well just get it out of the way. If this is the repair you need you will require an engine support frame - the kind that sits across the engine bay - this isn't a cheap piece of kit but it is a very useful tool to have.

 

I have a substantial hoist in my shop that my grandfather made ages ago from an I-beam and some stout metal legs with a nice little chain hoist on some rollers that I was able to use with a little bit of fabrication to support the engine when I pulled the transmission. I was just doing some reading and I guess pan was the wrong word for it. I guess the pan is in the back and readily taken off with the engine in place, with a sandwich plate? in the front. The thing I was reading on the jag lovers site said it is technically possible to remove without dropping the sub frame or pulling the engine. In either case it sounds like a cussing good time but oil leaks make my brain itch so I definitely will have to just fix it. That may sound obvious but I have to work with my uncle a lot and hes the sort that is perfectly happy to let an older vehicle just leak as much oil as it wants and just top it off regularly - considers those vehicles to be "self changing" and just replaces a filter every couple years.

How can I go about satisfactorily ruling out a head gasket issue? Any other time I know i've had a head gasket issue I always had either coolant or oil where it didnt belong and im not seeing any signs of that. I haven't done the test on the coolant yet, but im open to any other suggestions too. You mentioned doing a compression test, I have the tool for that so its in my list to do. As much of a pain as it will be to get those spark plugs out I kind of want to replace them at the same time but I can't do that right now so Im avoiding lol.

Most of my local parts stores will let you borrow a tool, you pay retail for it up front but as long as you bring it back in a timely manner they refund the full amount so its free. It can be annoying sometimes when you get tools that are missing stuff or damaged. I've borrowed bearing drivers a few times and actually had some in the kit that were broken in half. Im not even sure how that would happen. Free is free though lol.

 

How can you be sure - you can't - at least not with 100% certainty.

There's only four indicators - oil in water or water in oil, providing you don't have EGR coolers or as we do in rad oil coolers - re automatic in our case, then oil in the water may not be a head gasket problem (this one can destroy an auto transmission very quickly), combustion products in the cooling system - the gas test - if you run with the fill cap off with the thermostats open a steady stream of bubbles is a good indicator - this is what the gas test is looking for - but your nose isn't a good enough detector, cooling system pressure - should never exceed the cap rating i.e 15psi at any normal operating temperature, this pressure depends on cooling system capacity and design, to test it you put it under pressure then check again 30 mins or so later - but this does not prove head gasket unless you are 110% certain there are no leaks elsewhere - including your pressure test set up. It is actually a good thing to pressure test the system with no coolant in it - then you can go around with the bubble bottle - (Dawn solution or similar) - catch 22 is that some leaks won't appear when cold but this is one reason why the constant pressure spring clamps are way better than any 'jubilee' clip as they adjust with temperature and do not apply excessive force distorting the hose - many overtighten them.

An engine with a head gasket issue will tend to overheat or blow radiator hoses though not always, combustion gases are just about the best test but they do not 100% prove head gasket - merely that there is an issue present one such problem could be Cavitation Damage. Never Never Never use only ordinary water in an alloy engine - coolant is about way more than freeze protection.

And yes the plugs are a real pain in the butt - for one you need to blast out the crud from the holes, then you need to get through all the junk in the way with a suitable wrench - do not use power tools for this - you need to 'feel' the plugs and be kind of gentle until you're sure they're on the way out - constant resistance is not necessarily bad but if the bottom threads gall they will take all the others with them on the way out - don't let this scare you all aluminium heads have this issue because the plug is a dissimilar material. I use Aluslip on plugs I install in alloy heads. The biggest two that are a pain are the front two where the AC compressor is - remove the belt from the AC compressor you can jack it out of the way.

 

Aluslip? never heard of it. Is that just anti-seize or is there something special about it?

 

I will let the supplier describe - basically used anywhere galvanic corrosion is possible - copper slip is not suitable for such locations.

Aluslip