steam from exhaust and back of engine
Discussion
On Saturday my 1992 1.6 Eunos suddenly produced a huge cloud of steam (def. not smoke) from the exhaust on the overrun while driving on a DC, fortunately I only had a few miles to go and managed to limp it home. Temp gauge remained in the normal position.
Once stopped I found steam from the rear of the engine with spots of coolant on the coilpack / HT leads. Expansion tank was empty, rad was empty below the top hose but system was full from below the thermostat. Engine was recon about 5 years ago with new HG and shells and everything else inside tested, so I didn't do the internals but I did replace water pump, thermostat, all external oil seals, all hoses were new silicone etc...
I've now removed the head and the head gasket looks fine, no cracks in the head that are visible to the eye, the #3 cylinder had a lot of coolant in it and others were dry, and I noticed that one of the head bolts (3rd back on the exhaust side) was much easier to undo than all the rest, just felt nipped-up tight and didn't give that crack-release motion the others did.
Can anyone suggest my next step please?
thanks
James
Once stopped I found steam from the rear of the engine with spots of coolant on the coilpack / HT leads. Expansion tank was empty, rad was empty below the top hose but system was full from below the thermostat. Engine was recon about 5 years ago with new HG and shells and everything else inside tested, so I didn't do the internals but I did replace water pump, thermostat, all external oil seals, all hoses were new silicone etc...
I've now removed the head and the head gasket looks fine, no cracks in the head that are visible to the eye, the #3 cylinder had a lot of coolant in it and others were dry, and I noticed that one of the head bolts (3rd back on the exhaust side) was much easier to undo than all the rest, just felt nipped-up tight and didn't give that crack-release motion the others did.
Can anyone suggest my next step please?
thanks
James
Are you sure it was coolant getting into the engine? Steam at the back of the engine is usually one of the heater hoses leaking and spraying water, often onto the manifold which just adds to the steam. If you were driving on a DC the steam would be seen trailing behind the car so might appear to be coming from the engine.
No it was certainly from the exhaust pipe - I have an MX5Parts twin pipe and it typically produces more flow out of one side when cold (I assume because of the pipe layout) and it produced a great cloud of it from left rear pipe as soon as I lifted off the power from higher revs. Just To be sure I did it again twice, and it produced the exact same cloud of steam out of the left rear only on the overrun from higher revs. I had the roof down so I got a good view of it.
It was fine the day before, coolant level was perfect, so it managed to empty the expansion tank and top of the rad in about 3 miles, but there were no leaks appearing underneath. Hoses are farily new and good quality silicone ones and all fine as far as I can see, and no obvious rips or splits and no traces of large coolant leaks around the rear of the engine.
The steam around the rear of the engine was just a fine mist, causing a few small drops of coolant on the HT leads. The exhaust cloud was huge.
With the head removed yesterday there was a large puddle of coolant in cylinder 3.
It was fine the day before, coolant level was perfect, so it managed to empty the expansion tank and top of the rad in about 3 miles, but there were no leaks appearing underneath. Hoses are farily new and good quality silicone ones and all fine as far as I can see, and no obvious rips or splits and no traces of large coolant leaks around the rear of the engine.
The steam around the rear of the engine was just a fine mist, causing a few small drops of coolant on the HT leads. The exhaust cloud was huge.
With the head removed yesterday there was a large puddle of coolant in cylinder 3.
Edited by anonymous-user on Tuesday 12th June 10:05
Well I found the cause of the small amount of steam from the back of the engine - the tiny rubber blanking plug on the metal housing on the rear of the head had a small hole in it. I assume it's a pressure release of some sort and blew to relieve pressure in the cooling system, so now I need to find why it pressurized.
Cylinder head is off to be pressure tested for cracks tomorrow, hopefully that will shed some light on the issue.
Cylinder head is off to be pressure tested for cracks tomorrow, hopefully that will shed some light on the issue.
Yeah it had a genuine Mazda thermostat. In fact I replaced the entire cooling system and all the pipes and electrical sensors and external gaskets when I put it in the car.
The engineering company had a look at the head and gasket when I took it in - the yellow metal strips around the cylinders were darkened about half way around all 4 which apparently indicates constant but small leakage for a considerable while. There are also signs of coolant leakage right across one side of the gasket, although the gasket itself hasn't blown anywhere.
They could also see marks on the head surface indicating that it hadn't been skimmed before replacement last time, probably just brushed down or rubbed down by hand, and not very well either.
Guess I was lucky to get 5 years of constant thrashing out of it before a major leak occurred.
Anyhow, they're pressure testing it and if that's OK then they will vac test the valves and skim the head, so hopefully it will soon be back together and in better shape than it was when I got the engine 5 years ago. I also have a spare cylinder head somewhere from a previous engine so fingers crossed one of the two heads can be used again.
I would be annoyed if only I didn't enjoy pulling engines to pieces so much
The engineering company had a look at the head and gasket when I took it in - the yellow metal strips around the cylinders were darkened about half way around all 4 which apparently indicates constant but small leakage for a considerable while. There are also signs of coolant leakage right across one side of the gasket, although the gasket itself hasn't blown anywhere.
They could also see marks on the head surface indicating that it hadn't been skimmed before replacement last time, probably just brushed down or rubbed down by hand, and not very well either.
Guess I was lucky to get 5 years of constant thrashing out of it before a major leak occurred.
Anyhow, they're pressure testing it and if that's OK then they will vac test the valves and skim the head, so hopefully it will soon be back together and in better shape than it was when I got the engine 5 years ago. I also have a spare cylinder head somewhere from a previous engine so fingers crossed one of the two heads can be used again.
I would be annoyed if only I didn't enjoy pulling engines to pieces so much
Gassing Station | Mazda MX5/Roadster/Miata | Top of Page | What's New | My Stuff