Head Gasket / Cracked Head
Discussion
1.8 NA showing strange symptoms on start up. When cold there is lots of steam from exhaust with slight smell of coolant. When warm all symptoms disappear. Have done compression test (180/190/175/165), coolant block test (very slight colour change) and a coolant pressure test. Nothing conclusive.
Believe it to be head gasket (educated guess) but how can I tell if it's a cracked head?
Probably not related but no. 2 spark plug keeps fowling up. Any ideas? Cheers.
Believe it to be head gasket (educated guess) but how can I tell if it's a cracked head?
Probably not related but no. 2 spark plug keeps fowling up. Any ideas? Cheers.
I had a cracked head on my 1.6 - for months. Most symptoms were that the car would be difficult to start first thing, but okay once 'revved' - and strange random occurences of white smoke from the car, typically on the overrun after a long cruise (i.e. coming off a dual carriageway and coasting up a slip road).
It can show a variety of symptoms, there was only very slight real coolant loss with mine. What does the plug look like? Is it oily/black?
Only real test is to whip the head off and get it pressure tested at a local engine place. If it's okay worth getting it skimmed, if not it's junk.
Where are you?
It can show a variety of symptoms, there was only very slight real coolant loss with mine. What does the plug look like? Is it oily/black?
Only real test is to whip the head off and get it pressure tested at a local engine place. If it's okay worth getting it skimmed, if not it's junk.
Where are you?
Hi Fran- was hoping you'd reply to this as I saw a previous posting re something similar!
Changed all plugs about 200 miles ago; 1,3&4 are all perfect whilst no.2 is dark/oily. Any ideas?
Should also say that when warm does not overheat although it is a bit flat. Have checked timing belt and it's spot on although haven't checked dynamic timing yet. Cheers.
Changed all plugs about 200 miles ago; 1,3&4 are all perfect whilst no.2 is dark/oily. Any ideas?
Should also say that when warm does not overheat although it is a bit flat. Have checked timing belt and it's spot on although haven't checked dynamic timing yet. Cheers.
Hello Russ,
Oddly I think it was No 2 cylinder I had trouble with - the plug also decided to jam itself in place too, but agian I think unrelated.
What's the mileage on your engine? The compressions test results do show some wear (mainly on the difference in readings) - you cna check to see if the compression is related to valve seats or ring/bore wear by redoing the compression test dropping a teaspoon of oil into the cylinder before you attach the gauge - significant improvement in the reading suggests a bottome end proplem (rings/bore) - whereas if there isn't a restoration in compression it'd probably be valve related. I did find mine needed a good regrind in by hand (well, modified hand valve grinding stick in cordless drill after the first three valves caused near fatal hand blisters). Does your car stand for much time?
I don't know how adept you are at spannering (I'd claim however that it's never that difficult if you have the benefit of the manual and a methodical approach) - but if you can spare the hassle whipping the head off is likely to be the next stage. Cracks have a nasty habit of showing intermittent symptoms, like the start up only one, although mine did one day decide to give itself away by losing a load of water all of a sudden followed by a little mayonaise in the oil filler cap. Apart from that there was no overheating or other misbehaviour (except starting badly and randomn puffs of white smoke from exhaust).
Ask away if there is anything more you want to know. I have to say, pretty much all the fixings on my 1.6 1990 came apart without trauma of rounded heads, broken threads and the such like.
Oddly I think it was No 2 cylinder I had trouble with - the plug also decided to jam itself in place too, but agian I think unrelated.
What's the mileage on your engine? The compressions test results do show some wear (mainly on the difference in readings) - you cna check to see if the compression is related to valve seats or ring/bore wear by redoing the compression test dropping a teaspoon of oil into the cylinder before you attach the gauge - significant improvement in the reading suggests a bottome end proplem (rings/bore) - whereas if there isn't a restoration in compression it'd probably be valve related. I did find mine needed a good regrind in by hand (well, modified hand valve grinding stick in cordless drill after the first three valves caused near fatal hand blisters). Does your car stand for much time?
I don't know how adept you are at spannering (I'd claim however that it's never that difficult if you have the benefit of the manual and a methodical approach) - but if you can spare the hassle whipping the head off is likely to be the next stage. Cracks have a nasty habit of showing intermittent symptoms, like the start up only one, although mine did one day decide to give itself away by losing a load of water all of a sudden followed by a little mayonaise in the oil filler cap. Apart from that there was no overheating or other misbehaviour (except starting badly and randomn puffs of white smoke from exhaust).
Ask away if there is anything more you want to know. I have to say, pretty much all the fixings on my 1.6 1990 came apart without trauma of rounded heads, broken threads and the such like.
Stripped the engine down and replaced the head gasket. Whilst I was in there I did the timing belt etc etc. I also spent an hour stripping and cleaning the hydraulic lifters as they were chattering a bit on start up.
Sadly it's still showing some of the previous symptoms; occasional white exhaust.
No2 plug is also still fowling. Any ideas on what might be causing that?
Sadly it's still showing some of the previous symptoms; occasional white exhaust.
No2 plug is also still fowling. Any ideas on what might be causing that?
[/url]well, going on what the chap at the machining place said (and yours looks kind of similar) - I'd suggest No 2 top left exhaust valve lookes like it has suffered impingement from water droplets.
It may be poor combustion as a result of water ingress to the cylinder causing the blackening, or it may be oil coming up through the rings. If the cylinder has a substantial amount of water in it when the car is started, then it may have 'hydraulic'ed' which could have coused problems with the piston/rings too.
If you want to save doing another gasket change or further work that may not cure it, I can only suggest:
- Take the head for a pressure test (cost likely to be circa £25)
- Do a compression test again, one pass as is, second pass with the teaspoon of oil. Massive improvement on No 2 would suggest a bottom end problem too, and I guess if you had a head and a bottom end issue then cheapest way out is a second hand engine, although if you want the peace of mind, enjoy doing it and don't mind the extra expense you could rebuild this yourself.
Suggest you do the second before you whip the head off again.
What is the oil consumption like?
It may be poor combustion as a result of water ingress to the cylinder causing the blackening, or it may be oil coming up through the rings. If the cylinder has a substantial amount of water in it when the car is started, then it may have 'hydraulic'ed' which could have coused problems with the piston/rings too.
If you want to save doing another gasket change or further work that may not cure it, I can only suggest:
- Take the head for a pressure test (cost likely to be circa £25)
- Do a compression test again, one pass as is, second pass with the teaspoon of oil. Massive improvement on No 2 would suggest a bottom end problem too, and I guess if you had a head and a bottom end issue then cheapest way out is a second hand engine, although if you want the peace of mind, enjoy doing it and don't mind the extra expense you could rebuild this yourself.
Suggest you do the second before you whip the head off again.
What is the oil consumption like?
Interesting... I'm keeping an eye on mine veeeerrry closely at the moment, as I've got that inkling feeling something is starting to go.
I've had to top up the coolant just a touch, but it appears to be incrementally starting to burn oil.
No overheating, no mayo, but I'm still very wary....
The annoying thing is its my only car so I dont have the time to start just taking things apart, until im more sure somethings amiss...
I've had to top up the coolant just a touch, but it appears to be incrementally starting to burn oil.
No overheating, no mayo, but I'm still very wary....
The annoying thing is its my only car so I dont have the time to start just taking things apart, until im more sure somethings amiss...
Snotrag - I think it's relatively rare for the heads/gaskets to go, so I wouldn't start worrying yet. Jsut check your rad cap is in good order, anotehr suspicion of coolant loss without anything external making it evident - it can be the water pump (if you had the timing cover off then there may be evidence of waterstains under the pump) or a pinhol somewhere, a look round the rad (the matrix and the plastic end tanks) is also worthwhile. If the car is misting up a lot sometimes that is an indication that the heater matrix is becoming incontinnent.
Oil use - it seems some people have no oil use, some have consumption, clearly more prevalent in older cars. Too early to link oil use to a head gasket problem. My own experiences of head gasket failure ahve always led to water getting into the oil, not really any appreciable oil loss from the gasket failure.
Russ - if you are getting it skimmed, makes sure they do the pressure test first, which will prob be another £20-25. Be a shame to go to all this trouble and realise you'd just skimmed/reinstalled a broken head.
Oil use - it seems some people have no oil use, some have consumption, clearly more prevalent in older cars. Too early to link oil use to a head gasket problem. My own experiences of head gasket failure ahve always led to water getting into the oil, not really any appreciable oil loss from the gasket failure.
Russ - if you are getting it skimmed, makes sure they do the pressure test first, which will prob be another £20-25. Be a shame to go to all this trouble and realise you'd just skimmed/reinstalled a broken head.
My recent experience, not of an MX-5, but still a Japanese 4-cylinder, 16-valve engine (steel block, aluminium head), so may be relevant:-
Started to notice coolant loss, though nothing significant and couldn't see where it was going.
Found that the radiator cap was pretty rusty, so replaced it.
Radiator started leaking, assumed this was because the cooling system was now reaching a higher pressure and this had exposed a weakness in the radiator. Replaced radiator.
Still losing coolant, now really starting to suspect the head gasket. Took the car to a garage for a coolant test. No obvious colour change, so inconclusive. However, whilst up on the ramps we spotted a core plug on the block leaking.
Replaced core plug. Now everything in the cooling system was really pressure tight, so any weakness in the head gasket would be exposed. Started the engine, clouds of white smoke from the exhaust (looked like the Red Arrows had just gone past).
So, I'm currently starting to put everything back together after getting the head skimmed & fitting a new head gasket. I'm just hoping that there's nothing else (more serious) that I've missed, such as a cracked block. I'll know at the weekend....
Started to notice coolant loss, though nothing significant and couldn't see where it was going.
Found that the radiator cap was pretty rusty, so replaced it.
Radiator started leaking, assumed this was because the cooling system was now reaching a higher pressure and this had exposed a weakness in the radiator. Replaced radiator.
Still losing coolant, now really starting to suspect the head gasket. Took the car to a garage for a coolant test. No obvious colour change, so inconclusive. However, whilst up on the ramps we spotted a core plug on the block leaking.
Replaced core plug. Now everything in the cooling system was really pressure tight, so any weakness in the head gasket would be exposed. Started the engine, clouds of white smoke from the exhaust (looked like the Red Arrows had just gone past).
So, I'm currently starting to put everything back together after getting the head skimmed & fitting a new head gasket. I'm just hoping that there's nothing else (more serious) that I've missed, such as a cracked block. I'll know at the weekend....
Fran - Im with you there. As I said, no other signs of it being a leak in the head.
Oil consumption is well within what I guess is acceptable for an old car, especially given that it gets regular, prolonged thrashings at high revs. (Its the only way
)
I actually had a root around underneath today - I think Ive got a very small coolant leak on the lhd side of the engine bay somewhere, which would tie in with a lower rad pipe, or heater matrix possibly. Radiator is new, Rad cap looks a bit rubbish.
I think its likely a perished pipe, which will be difficult to pin down until it inevitably goes pop one day. Not a lot I can do other than keep checking it really.
Oil consumption is well within what I guess is acceptable for an old car, especially given that it gets regular, prolonged thrashings at high revs. (Its the only way
) I actually had a root around underneath today - I think Ive got a very small coolant leak on the lhd side of the engine bay somewhere, which would tie in with a lower rad pipe, or heater matrix possibly. Radiator is new, Rad cap looks a bit rubbish.
I think its likely a perished pipe, which will be difficult to pin down until it inevitably goes pop one day. Not a lot I can do other than keep checking it really.
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