simonwref Posted April 6, 2011 Report Share Posted April 6, 2011 im no car expert so first question is, what is a head gasket and what does it do? i suspect that its gone in my gen5 so now im wondering, what causes a failure? is it just wear and tear, one of those things. do they have a service schedule? also wondering, if i missed any symptoms that could have led me to realise, as i suspect that the HG went first and caused the radiator to pop, rather than the other way round, i maybe drove 2 miles before i noticed the temp had maxed and stopped, and surely if it was just the radiator going pop, it wouldnt do that much damage in such a short time, and also the radiator was replaced with a new one, just over a year ago. also wondering, in future, is there any advice on preventing it happening again whether that be in this car or a new one. ive heard about replacing with metal ones? Link to comment Share on other sites More sharing options...
mutznutz Posted April 6, 2011 Report Share Posted April 6, 2011 The head gasket sits between the block and the cylinder head, its to ensure max. compression and to help stop leaks of oil / coolant into the cylinders. Some symptoms are white smoke on starting up and also can have crud in the oil filler cap (not always though). When it fails the oil / coolant gets where it shouldn't. Not sure about the other questions ... I hope that helps and someone more knowledgeable will answer the rest / correct me Link to comment Share on other sites More sharing options...
Dorris Posted April 6, 2011 Report Share Posted April 6, 2011 The head gasket (HG) is gasket that sits between the cylinder head and the block. On the Gen 5s they are made from a fabric material, both mating surfaces have to be dead flat, can't remember the tolerance of the top of my head. They are not something that can be serviced and the reasons they fail can vary, the most common is over heating caused by another problem causing the aluminium cylinder head to wrap and distort, this breaks the seal between the head and the block so allowing the cylinder pressures to escape into the coolant or oil systems. As for symptoms the common ones are lots of white steam from the exhaust, coolant expansion tank pressurising and blowing out coolant or oil being forced in to the air box as the oil system pressurises. Another symptom can be mayonnaise like substance within the radiator as the coolant and oil mixes but this can also be caused by short journeys and excessive condensation within the oil. If it is the HG I'm afraid there is no easy fix, it's a partial engine strip, cylinder head off, mating surfaces will need to be checked and probably skimmed flat again and a rebuild. You can get metal head gaskets but these can be expensive for an aftermarket part and no benefit to a normally aspirated engine like the Gen 5 Yamaha 3SGE engines. Hope this helps, Dorris. Link to comment Share on other sites More sharing options...
Gen6GT Posted April 6, 2011 Report Share Posted April 6, 2011 A head gasket is basically a shim which can compress slightly, so that a seal is formed when the cylinder-head is torqued down onto the cylinder block. Unless both the block-face and the cylinder head face are perfectly flat you will always need a head gasket to take-up and slight machining differences between the two. They are not subject to wear and tear, since there are no moving parts to cause them to leak, however if your car has, at some time, run with very little coolant, or has frozen-up, both of these can cause the head gasket to fail, since the engine block and the cylinder head can, under these kind of circumstances, expand/contract at different rates causing warpage, and if the difference is big enough the gasket seal can fail. A compression test on each of the cylinders may point to where the problem lies, also, as has been said, you may well see white crud (oil/water emulsion) forming on the oil filler cap, caused by coolant from the cooling system finding it's way through the failed head gasket into the oil circulation system. If you are not mechanically-minded, and it would seem so, probably your best bet would be to find a local small garage who can advise you. Link to comment Share on other sites More sharing options...
Angus Posted April 6, 2011 Report Share Posted April 6, 2011 Be a good chap, and go to the Gen 5 Forum. On arrival, open the FAQ post at the top in the stickies. Inside this post, you'll find links to several past Head Gasket threads, at least one of which includes pictures similar to what Dorris just posted up. As for preventative maintenance, short of taking the rocker cover off and checking the torque on the head bolts there's not a lot you can do. There are various causes, probably the most common of which is overheating of the engine by loss of coolant - causing either heat damage to the HG itself, or warping of the aluminium cylinder head by heating - which causes a wee gap through which stuff can get where it shouldn't. And yeah, metal head gaskets can be had. Again, look at those Gen 5 threads for some more info on that. Angus Link to comment Share on other sites More sharing options...
Alan Clogwyn Posted April 6, 2011 Report Share Posted April 6, 2011 It's just a gasket like any other, a squidgy thing to fill the gaps between two components to make a perfectly tight seal. There are holes in it for the cylinders and passageways for oil and water to reach the head from the block. Some engines don't have seperate cylinder heads and therefore have no head gasket, which is pretty cool. Why do they fail? Pressure and heat. Both surfaces of modern HGs are coated in a glue which bonds them to the head and block. Get the engine hot and this glue melts, lets gas through and pop that's your headgasket gone. This is a minor failure, wouldn't kill you car on the spot dead but would make it pretty unhappy. The other way is as above, a Major overheat warping the head so that theres no hope of a gasket sealing the gap. Symptoms? Depends on engine design and the exact nature of the fault in the headgasket. On both my Celicas the leak in the gasket went only as far as the cooling jackets. The grey one was severe enough to cause a loss of compression that eventually killed it. On the brown one the leak was much much smaller, and all that managed to do was pressurise the cooling system, causing it to blow out all the coolant and eventually overheat. A really severe headgasket problem could potentially allow coolant and oil to mix or enter the combustion chanber. This is characterised by emulsified gunk in the coolant or oil or both (mayo). This is rarer than people think. What might indicate a problem with the head gasket/how to diagnose it? Well unexplained overheating is usually a warning. with the rad cap off and the engine running, if the water's bubbling away then the HG is kaput. a bubble every now and then is not a problem as moving water does make a few bubbles, but if it looks like someone blowing down a straw into their coke wit hice then it's bye bye HG. Low compression is another indicator but its' not a foolproof test. You can get a Headsaket tester which is basically a liquid that changes colour in the presence of combustion gasses, you use it over the open rad cap and i ttells you if theres a leak through. The Brown Cdelic proved very difficult to diagnose as when it was cold it showed no symptoms, only when it got warm did the leak show itself in the cooling system. Link to comment Share on other sites More sharing options...
Angus Posted April 7, 2011 Report Share Posted April 7, 2011 The Brown Celica proved very difficult to diagnose as when it was cold it showed no symptoms, only when it got warm did the leak show itself in the cooling system. Yep, my 185 was the same. It could toot along happily for 100 miles on open roads, but overheated as soon as it hit boost, or had to climb a steep hill, or was stopped at traffic lights for a while when hot. Angus Link to comment Share on other sites More sharing options...
Recommended Posts