1996 Mazda Mx5 with ITBs - p16 video clip :)

That there is a photograph which should send shivers down the spine of any rotary owner. It's a front rotor leading plug, and it's wet with coolant.

So yeah over the past couple of weeks I've been noticing various slightly worrying symptoms; coolant is going missing, the coolant overflow is getting very full, the engines blowing bubbles into the coolant overflow and it's been a pain to start. It would start every time on 1 rotor, with the second joining in ~10 seconds later, and when hot it also kicked out a lovely big cloud of steam.

Basically, short of spitting all the coolant out, overheating and smoking/streaming like mad the whole time, lots of classic signs of a water seal failure. Water seal failure is sort of equivalent to head gasket failure, its a full engine rebuild job to fix. Cranking the engine over once or twice (without ignition on), then pulling a plug is a easy way to see if anything is getting in the chambers. Turning it over makes the axel seals spread anything thats collected at the bottom of the housing around the place. Thats the test that created that nice wet plug up that and put the fear of god into me.

After having a mild panic, I decided on a plan of action. The O rings which seal the coolant pathways between the intake manifold and engine block had sprung a leak after my first initial shake down drive. It seemed cured by nipping up the intake manifold bolts a bit more, but it was time to be sure and these O rings are the only other way that coolant can leak inside the engine, besides the dreaded water seal failure.

I wasn't going to take any chances with the O rings this time. I ordered some core plugs to permanently block up the coolant passageways into the intake manifold. Originally the coolant flow through the manifold would go off to feed the turbo, but as I've bypassed the coolant flow through the throttle body, I can always use that to feed the turbo should I ever get round to fitting one. Anyway, core plugs are cheap and it didn't take long to get them fitted.



Made no difference. So yeah, its a water seal failure. The fact that it wasn't overheating, nor was it steaming too badly from cold suggests that its in the early stages, but still not good. It was also worrying me that this is now the second engine to suffer front water seal failure in this car, so was there a reason?

While poking around in the engine bay last night, watching the bubbles in the coolant expansion tank, I came to realise that the radiator cap wasn't holding pressure. Even when the engine had cooled right down, if I even lightly squeezed the coolant hoses it pushed coolant/bubbles out into the expansion tank.

I think thats probably the cause No pressure in the cooling system will lower the boiling point of the coolant, which could mean it's boiling by the exhaust ports, allowing the water seal to overheat, and fail. So off to the local motorfactors this morning… new cap on the left obviously



Unfortunately my chinese eBay aftermarket radiator needed a cap very similar to an mx5 one but with a bit more reach, so I had to pull the new cap apart and space it out a little. Sounds dodgy but it's worked perfectly. The new cap is sealing well and holding pressure like to should. Still, whilst thats a nice and cheap fix, theres still the water seal issue.

Having neither the money or enthusiasm right now for a rebuild project, I took a chance on a bottle of k-seal. I've read mixed things about coolant sealants with rotary engines, there's some success stories and some failures and some scare stories but I figured I didn't have much to loose at this stage. Anyway I chucked it in and went for a drive. Stopping at the petrol station, a regular occurrence (more on this later), it restarted perfectly on 2 rotors with no steam! I've been finding excuses to go for a drive all day, and i've done ~60 miles and a number of stops then both hot and cold starts and so far it's lost no coolant, it's not blowing bubbles in the expansion tank, it's starting cleanly and quickly on both rotors every time and I did the plug test and it's bone dry. So tentative success, wooo!

So yeah aside from worrying about the water seals I've spent the past fortnight just using the car. I'm averaging ~21mpg over that period with a mix of driving, it's been feeling like I've been visiting the petrol station pretty often! Predictably, now I've got my nice uneconomical car up and running, I've been offered some work down London way, about a 200 mile round trip. £250 a week in fuel just to get to work isn't unreasonable is it? hahahaha

Cheers George, I hope so too!

I'm not sure on the hydrolocking front. I do know that they can run with surprising amounts of water getting inside the engine, some water seal failures are so bad they spit water out of the exhaust at a fair rate. With fairly low compression ratios and no con rods to bend I guess they're more resistant than your average piston engine. That said I'm not going to dump a pint of water into my intake to try it out… haha

I curse word love this and hope it ain't to much of a problem for you. You have worked wonders on this and quick time too. I worked at Mazda main dealer for a few years and have fond memories of all their cars, well some of them. Good luck sir...

Yeah I know rotors can do weird things, I was trying everything I can think of that could have caused it to loose coolant!

The radiator cap was 100% shot, it definitely wasn't holding any pressure. After I core plugged the inlet coolant feeds, I went for a drive and then took the inlet back off, and it was 100% dry, so the only way the front rotor plugs could have been getting wet with coolant, was through a water seal leak.

So far so good since the K-seal though. No coolant lost, started again perfectly this morning despite the cold, no excess smoke/steam.

Cool, glad to hear a positive thought on the k-seal Yeah 21mpg is about what I expected, I've just forgotten how often I need to fill up with a car doing ~20 mpg rather than the 35-40 of my recent cars!

Today I've basically been driving about all day, roof down in the cold, was lovely tonight in the dark. Dan_betG and I went out and played with my camera this afternoon and I was pleased with these couple of shots There's lots of nice pics of Dan's car but I'll let him post them himself

Bro that second picture is mean aye! Rugged as. I take it Dan's car is parked on a slight slope and he hasn't raised the back end up?

Wow had a lot to catch up on in this thread.

Glad you've got it on the road. Hope the k seal sorts it until you can rebuild.

Rotaries fascinate me but also scare the hell out of me haha.

You can always strip it down and just replace the seals- That's what i did when i discovered the frost damaged centre plate. In fact I only needed new inner seals. You can reuse the outer ones! They expand and get longer but also slightly fatter. I think they swell overtime. I just cut a section out, super glued it back together and made sure the join was at the top in the coolest part of the cycle. Never used a drip of coolant. Saved me many monies on what was a budget special.

Since last weekends fun and games with the cooling system, this week has been smooth sailing I've got in the car, turned the key and its worked, and I've driven places, and the driven home! How novel

That said, I'd been a little worried by a lot of negative experiences with K-sela that were coming out on one of the rotary forums I'm on. The concern is that the K-seal remains 'active' and that it can start to block up coolant passageways that aren't meant to be blocked, with that in mind I figured I'd do a coolant change and flush. The K-seal has done its job and sealed the coolant leak, so now I should be fine to flush any excess out and put fresh coolant in and it should give it the best fighting chance at working happily for a while longer.

When Id dropped the coolant and got the rad hoses off, I was pleasantly surprised to see that the k-seal didn't seem to have started collecting anywhere it wasn't meant to.




Certainly no blocked passageways in the rad there. This is all after having k-seal in the system for 1 week and about 200 miles. Anyway, still seemed sensible to flush it all out…



I got it back together and filled it with fresh coolant and have done about 70 miles since, still working just fine. So that's promising.

While I had the car in bits, I decided to give it a once over. Its done ~1000miles seance I got it back on the road, so it's had a good shakedown! I was pleased to find that most things had stayed tight, only the upper ARB drop links seemed to not be as torqued up as I expected. I have been getting a light nocking front the front left, and was hoping that doing a retorque of all the suspension band brake components would stop it, but it hasn't. I wonder If the wheel bearings on the way out, add that to the to do list!

I also removed one of the rear toe hooks, as it had been catching against the exhaust.



For a mk1 mx5 my car is now surprisingly rattle/knock free! Always a good thing. The road noise is starting to get on my nerves though, it's dreadful at motorway speeds. I'm currently running without any sound deadening under the carpet because the mice had eaten it, but I think refitting some is moving up the priority list