Exhaust manifold leak

[Masher]

I have an exhaust manifold leak and also slightly rough running while trying to keep to the 30 - 40 MPH speed limits, once the revs rise to proper road speeds things are OK. Could these two things be related??

Before anyone says 'you shoud get the manifold leak sorted' I know I should but am a bit skint at the moment. I only got the car (1995 4.0) a few weeks ago and was not looking for one but could not resist when I was offered the car at a very good price. While on the subject, has anyone had dealings with TVR Fix as they are not to far from me and I was thinking of having them do the manifold gaskets.

[Barreti]

If the manifold gasket is leaking you really shouldn't be driving the car because you risk damaging the head if you do due to the massive amounts of heat being forced through between the head and the manifold. The head is ali and the heat can melt grooves around the port. Well, so I'm told by 'them in the know'
Its not a complicated task to replace the gaskets yourself if you've got some axle stands to prop the car up so you can get to the bottom manifold bolts. If you are vaguely competent with spanners you should order the gaskets now and have a go yourself when they arrive.

Whichever, I hope you get it fixed quickly and get back out there enjoying it

[andy-w]

Barreti said:

The head is ali and the heat can melt grooves around the port. Well, so I'm told by 'them in the know'

Hmmmmmm..why would escaping gasses melt the head when the gas passes through the exhaust port with no damage?

Plus side - a leaking manifold should help with the pops and bangs....

[350Matt]

andy-w said:

Barreti said:

The head is ali and the heat can melt grooves around the port. Well, so I'm told by 'them in the know'

Hmmmmmm..why would escaping gasses melt the head when the gas passes through the exhaust port with no damage?

This does happen even on cast iron heads, the gas that normally charges down the exhaust pipe doesn't have time to heat the head in this area, around the port inside the head its cooled by the water jacket.Mainly though the wear mechanism isn't really melting, its more cavitation as the leaks are invariably very thin gaps so the gas speed is very high through them which then plucks material front the surrounding walls


Matt

[That Daddy]

350Matt said:

andy-w said:

Barreti said:

The head is ali and the heat can melt grooves around the port. Well, so I'm told by 'them in the know'

Hmmmmmm..why would escaping gasses melt the head when the gas passes through the exhaust port with no damage?

This does happen even on cast iron heads, the gas that normally charges down the exhaust pipe doesn't have time to heat the head in this area, around the port inside the head its cooled by the water jacket.Mainly though the wear mechanism isn't really melting, its more cavitation as the leaks are invariably very thin gaps so the gas speed is very high through them which then plucks material front the surrounding walls


Matt

Yes and the by products from combustion dont help eitherthis also happens on cylinder heads that have been left for a period with a blown headgasket near the fire ring area

[Masher]

Thanks for the science lesson, I have now ordered the gaskets as I dont want a bad fire ring....

Back to the original post, could the leaking gasket have also caused the rough slow running problem??

Thanks

Mike

[That Daddy]

Masher said:

Thanks for the science lesson, I have now ordered the gaskets as I dont want a bad fire ring....

Back to the original post, could the leaking gasket have also caused the rough slow running problem??

Thanks

Mike

Just trying to explain why it should not be left blowing,but you seem to know what your doing as you put the post up for opinions anyway

Edited by That Daddy on Tuesday 3rd July 13:54

[Masher]

That Daddy said:

Masher said:

Thanks for the science lesson, I have now ordered the gaskets as I dont want a bad fire ring....

Back to the original post, could the leaking gasket have also caused the rough slow running problem??

Thanks

Mike

Just trying to explain why it should not be left blowing,but you seem to know what your doing as you put the post up for opinions anyway

Edited by That Daddy on Tuesday 3rd July 13:54

I was being sincere, I know it does not happen much anymore. As you can see information greatfully recieved and parts ordered.

[That Daddy]

Masher said:

That Daddy said:

Masher said:

Thanks for the science lesson, I have now ordered the gaskets as I dont want a bad fire ring....

Back to the original post, could the leaking gasket have also caused the rough slow running problem??

Thanks

Mike

Just trying to explain why it should not be left blowing,but you seem to know what your doing as you put the post up for opinions anyway

Edited by That Daddy on Tuesday 3rd July 13:54

I was being sincere, I know it does not happen much anymore. As you can see information greatfully recieved and parts ordered.

[GreenV8S]

An exhaust manifold leak on a catted car can cause rough running at low revs by allowing air to get sucked into the exhaust and throwing the lambda reading out. But you should also know that it's quite common for these engines to get a bit lumpy and start shunting at low revs. How low you can go before you run into trouble depends on the state of the engine, and how much backlash there is in the transmission, and lots of other things. But typically there will be a point somewhere around 1500 rpm where it starts to get unhappy. Although the engine has enough torque to pull the car along easily at those revs, it isn't good for the engine and you're better off changing down and giving it slightly more revs.

[Timja]

andy-w said:

Barreti said:

The head is ali and the heat can melt grooves around the port. Well, so I'm told by 'them in the know'

Hmmmmmm..why would escaping gasses melt the head when the gas passes through the exhaust port with no damage?

Plus side - a leaking manifold should help with the pops and bangs....

Can anyone explain why does a leaking manifold help with the pops and bangs?

Mine is in having new gaskets at the moment (assuming i dont get a nasty call to say manifold cracked!) - I don't want to loose the pops and bangs though!

[GreenV8S]

Timja said:

Can anyone explain why does a leaking manifold help with the pops and bangs?

Some fuel comes out of the engine un-burnt when you close the throttle, and allowing air into the exhaust enables this excess fuel to ignite.

[Timja]

Cheers. Will see what it is like when i get it back - hopefully it will still pop a bit! - Thats my favourite bit!