Blown Head Gasket

[Grob]

Hi, recently purchased a 4.2 Cerbera which has run fine for 200 miles but is now running v lumpy:
- Idle is erratic, dropping to 600rpm and then cycling up to 1000 every 1 sec or so
- Misfiring when holding constant speed in gear at low rpm
- More than usual 'popping' from exhaust
- MIL light has come on after a recent journey of 20 miles but went out at next start. Then comes on intermittently but is now off
I thought I'd check it on the diags but the laptop has a dead batt and there doesn't seem to be an obvious place to plug in the 9-pin connector
More worryingly, I've lost a bit of water and the dipstick has a small amount of creamy gunk on it so I suspect a blown head gasket. Have read lots of threads but the V8 doesn't seem to suffer from this, but I guess any engine can blow a gasket.

Questions:
- Would the MIL detect a blown gasket?
- How easy are they to replace?
- The engine's done 48K so would I be better off doing a rebuild? (I hope not!)

Thanks in anticipation

[itiejim]

Grob said:

Questions:
- Would the MIL detect a blown gasket?
- How easy are they to replace?
- The engine's done 48K so would I be better off doing a rebuild? (I hope not!)

Hi

Wow, that's bad luck after 200 miles, can't you go back to the seller in some way?

In answer to your questions:

1. The MIL won't detect a blown HG, however, it may indicate the poor running that comes as a result of one. Before taking drastic action though I'd put a sniffer on it or at least get a second opinion.

2. The head gaskets are, in themselves, quite easy to replace. The bad bit though is that you have to remove the engine to get the head off...

3. 48K shouldn't necessitate a rebuild, however, given that the engine is coming out you'd be mad not to have a little look - and replace the big ends... and check the bores... and while you're there put some rings in.... and change the clutch... and, you know the engine needs to come out to change the oil / water pump, so you might as well get that rebuilt while you're there. Engine out is also a good time to refurbish all the front end of the chassis.

Do you see where I'm going with this one? I rebuilt mine over the winter and did all of the above and more, so if you need a steer feel free to ask!

[Grob]

Thanks for the reply. Bu**er! Just been running the engine and there is some water coming out of the left exhaust and the gases are colder than the right so it would seem that a cylinder or two are not 'performing' as they should. Was hoping it was something simple. I'll still get the diags on though as the MIL should never have come on so there is obviously something else amiss.
I don't mind putting the effort in myself to do the rebuild work but may I ask what I can expect it to cost?

[Gazzab]

I have some expertise in (paying for) rebuilds.
Suggest if you need a basic rebuild / refresh plus a few extras (eg water pipes, clutch and chassis work) then allow £6K.
If you can do much yourself then you could possibly knock a couple of K of this.

[itiejim]

In terms of cost, it depends what you do. If you just take the engine out yourself, skim one head and replace one gasket, then you can probably do it for £200.

The problem is, as I indicated earlier, what else you do while it's out. My experience of stripping the whole engine down and doing absolutely everything that was required (it's a long list) along with lots of other tidying, improving and "I've started so I'll finish" bits meant that I spent about £4k...

[vroom]

Grob said:

Thanks for the reply. Bu**er! Just been running the engine and there is some water coming out of the left exhaust and the gases are colder than the right so it would seem that a cylinder or two are not 'performing' as they should. Was hoping it was something simple. I'll still get the diags on though as the MIL should never have come on so there is obviously something else amiss.
I don't mind putting the effort in myself to do the rebuild work but may I ask what I can expect it to cost?

Get it on the diagnostics before thinking / assuming the worst

Spitting water is normal on warm-up when you have cats - it's part of the process.

[JensenA]

Remember an engine produces something silly like a a gallon of water for every gallon of petrol used, so water coming out of the exhaust when cold is normal. That's why exhaust systems rot.
Before assuming it's a head gasket failure, check the breather hose to the driver side air box, it may be blocked, in which case clean it.
If it is a HG failure then your oil level will be going up and the coolant level going down - are you having to top up the water all the time? A simple sniffer test at a garage will confirm it one way or another - fingers crossed

[Grob]

Thanks chaps, greatly appreciated.
Water has gone down v slightly, oil up a tad, again v slightly
Water coming out of left exhaust more than right but as you say could be the cats
Biggest clue I think is the creamy oil on the dipstick

I'll check the breather (thanks for that tip) and do the diag (if I sort out the connector!) and then get it checked by a garage before I go borrow a hoist................

Will let you know

[Gazzab]

Woudl recommend you use a TVR specialist - nearest to you include Raceproved and Trackvroad.