Air leak noise after shutting engine off

[Stag3L]

Hi Everyone,

I noticed a new sound under the bonnet yesterday which I'm wondering about. I have a 3L original engine with BW35 transmission.

About 30-60secs after I turn the engine off I hear an air hissing (ingress or egress I can't really tell) near the rear spark plug on the drivers side. Its on the outside of the engine block so not the inlet manifold, but rather the exhaust manifold or maybe the cylinder head gasket or the spark plug itself.

Is this something I need to investigate further? It always occurs in the same location on a hot engine and only starts about 30secs after I turn the engine off. When I first turn the engine off then all is quiet. The air hissing lasts for about 60-120secs depending on how warm the engine is.

My car is otherwise running fine seemingly, not overheating at all, no smoke in the exhaust and plenty of power.

Thanks again.

[Staggard]

Sounds like a servo leak maybe a pinhole in the hose or something along those lines.

[flying farmer]

I wonder if it is water escaping from the head gasket joint and dropping on the hot exhaust manifold and hissing as it boils off? I once saw this on a Stag that had just been parked up at an event.

Heat soak from the engine after it has been switched off will give an increase in cooling system pressure for a short while which may just tip the leak/ no leak balance.
Another possibility is an air leak from the brake servo which is in the same area.

Edit

Staggard beat me to the servo leak

[mole42]

Brake servo

[Stag3L]

Should I be investigating the servo unit itself or the pipes to/from it? What are the Rimmers refurb kits like if the issue is the unit itself?

What are the implications of running while I have this slight vacuum issue (albeit only after shutting the engine off seemingly)?

Thanks again.

[trunt]

The pipes are open to the manifold and dont hold a vacuum after the engine shuts off so they are probably not the cause of the hissing.
If its from the servo area the first thing I would check is the non-return valve at the servo, its where the vac pipe enters. If that's leaking it would loose the vacuum like you describe. Whip the hose off, stick your finger over the pipe into the servo and see if the hissing stops..

Also if you have A/C there is another vacuum vessel for that, same deal, it has a non return valve on it that could leak.

As to rebuild kits, it looks to be a bit of a job..

http://www.buckeyetriumphs.org/technical/Brakes/Servo/Servo.htm

I'm brave on these things but once I found a place here in the USA that did it for $190 I just sent it there.. especially as The rebuild kit is $130 from Rimmer..

Terry

[Marco Polo]

Do you have the Triumph or after market aircon fitted? If you're not sure send us some piccys of your engine bay and or centre console. Where in Aus are you?

regards,
Raoul

[Stag3L]

Stag_1.jpgStag_2.jpgStag_3.jpg

Hi there,

Thanks for the replies. I (think) I've added some pics from my engine bay this evening.

I spent a bit more time trying to pinpoint the location of the noise. It definitely sounds like it's coming from really near the spark plugs. I've circled the location in red on the attached pictures. Which I'm guessing sounds more like Flying Farmer's thought that it might be a bit of coolant seeping out of the head gasket, then the hissing is actually it evaporating from the hot exhaust. It's really hard to pinpoint an exact location.

As ever, it is quiet when i turn the engine off then about 30-60secs later is starts this hissing noise which lasts for around 120 secs or thereabouts.

If it is the gasket leaking should I be driving it at all? Or straight in for service? As above it is driving perfectly well at the moment just this noise after shut down has me worried.

Thanks for the replies.

[Stag3L]

Hi everyone thanks for your replies. I tried to post a couple of days ago but I think it got lost somehow.

Anyhow I have had another look and am seeinf exact same symptoms. About 30-60secs after shutting off engine i hear this air hissing type noise for about 60-90secs.

Attached are a couple of pics. I've circled in red where the noise sounds the loudest. It's near (or even below maybe) the bolt between the spark plugs, its quite a difficult noise to track down to be honest (i.e. to tell exactley where the sound is coming from).

This location makes me think Flying Farmer might be right with the idea that some coolant escaping from the head gasket?

Should I be driving like this or straight to the workshop? As before the car is seemingly running just fine, its just this noise after I turn the engine off.
Stag_3.jpg
Stag_1.jpg
Stag_2.jpg
Stag_3.jpg

[flying farmer]

If it is a coolant leak causing the noise I would try some sealant tipped into the cooling system to begin with.

Don't know what you can get in Australia, but over here a lot of people recommend K seal, though I think most sealants will fix a small leak.

If you have a torque wrench it might be worth re torqueing the head bolts, slack them off half a flat before retorquing, the gaskets can compress over a period of time leaving the bolts loose.
Leaks in this area can be caused by corrosion of the heads gradually eating its way out to the edge of the gasket, but a dose of sealant might buy you years of use before a rebuild is necessary.
Neil

[1973_V8]

Ok everyone thanks for the messages. For good measure I thought I’d comment on what the issue was.

Turned out that Flying Farmer was correct - it was coolant escaping the head gasket and hitting the hot exhaust, making a hissing noise ss it evaporated. Rather than K-Seal I wanted to fix it properly (I did re-torque initially without success) , so Heads off, no sign of any other damage and so not a disaster at all. In fact, it was a good chance to fix up a bunch of other little things while I was in there. Heads skimmed, new gaskets all round etc.

Thanks again for all the comments.

Not