1500 kilometres after I last serviced it and topped off the coolant (I've had a persistant weep 'somewhere' since the engine was replaced - probably on the hose connecting the bottle because there's some crystal there and the engine always smells of it) I noticed the heater had stopped working. Engine temperature was OK, kept going -- assumed it was either an actuator issue or was just being finnicky, Turned the temperature up and it started working. Up until I was about a kilometre from home and it started blowing cold again. The coolant temperature needle had also subtly moved - but settled back the moment I switched the AC off. (Another thing this car has always done for 8 years, no matter what engine it had). It then moved a notch again. Not far enough to notice - not if I hadn't been looking for another symptom.

Fortunately, I was home at this point. Literally 200 yards to go.

Checked coolant temperatures after 10 minutes unloading the car, and it had already dropped to 80 degrees which would be the normal running temperature of the engine after a long cruise. No pressure blast when I opened the bottle. Happy days. It probably didn't truly overheat.

It ate about 2-3 litres of coolant to top it up (I have no idea what was left in the bottle after 3 years) and, when started, seemed relatively normal aside from a lot of condensation out the exhaust - which wouldn't be unexpected given it's 4 degrees out and raining . Started it up, the levels dropped a bit in the tank (Which I'd expected), topped it off again a bit, and the heater started working again. Seems to be OK. Hasn't dropped in an hour, and is circulating fine when I restarted the engine and let it warm up to about 90 again

I don't know what to do now. Send it to a local mechanic to look for the leak maybe - but it's not obvious at all - no obvious stains. Oil is clean - suspiciously so.. Car doesn't smoke. Whatever it is, it'll probably be bloody expensive. Which I don't really have right now because I lost a lot of money recently, so it might aswell be goodbye.

I got fooled by the stain on the bottle - it didn't look empty until I actually opened it and looked in.

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I've overheated it on the previous engine before --- always when in rolling traffic, or idling in traffic, and only ever with the AC on. So long as I turned the AC off and heater on, it always came back rapidly, and driving it out of it always cooled it down far better than letting it sit and hot soak. Provided the coolant system was intact - which I knew it was when I got heat out of it. What killed that engine was a broken sparkplug going for a spin inside it.

 

If it was at 80 degrees and you didn't get a pressure blast when opening the bottle, your cooling system isn't pressurizing (which makes sense considering there's clearly a hole somewhere). Coolant bottle neck would be one common failure point, you might also check the water pump weeping hole. If there's new coolant traces at the bottle/hose connection (which one?), I feel like you already know the answer.

If it was my car I'd get a good look and find where the coolant is coming out. Bottle? Water pump? Freeze plug? Radiator? Block drain? Coolant deposits on the spark plugs? It came out somewhere, you need to find that somewhere. You can take it to a mechanic, but in most cases you're paying them to learn guess about rotaries at that point.

 

There was a ****-ton of air in the top of the system so I wouldn't be too surprised if it didn't truly pressurise at 80 degrees. The volume change isn't that big at that temperature and there's 3 litres of air in the system.

It's the small hose to the top corner of the bottle that goes back towards the engine. It's only a small quantity of crystal so I never paid attention to it because that hose is generally above the coolant level so it'd be a vapour leak. Plugs were clean when I last changed them - back in November and it hasn't been run much since then - it spent most of December idle. It had a bad leak when the engine was first swapped, from a loose hose at the thermostat, but that was a warranty fix after the engine swap.

It's too damned dark to see more and with the working hours I'm on it will be until the middle of next week. But it's not marking it's territory with stains or having any obvious puddles on it while sitting. It's not having starting problems - or giving clouds of smoke while running. There's no gunk on stick. None on the plugs (recently) and there's a definite smell of hot coolant off it when shut down after a long run so I'm guessing it is (or was) outside the block.

Could it just be boiling and venting?


There is a local specialist that's reasonably well regarded - I can send it there and - worst comes to worst - it can join the spare-parts herd.

 

Update:

There's some old evidence of a leak around the thermostat. But it's not there. That was fixed 3 years ago. There's a small, long dry weep on the bottle inlet at the top that's minor.

It's the coolant vent cap. Got it good at hot - up until the fan came on and it began to steam. OBD said 96 degrees which was right. Spent an age looking for the leak - and sniffing for it - getting huffs of steam from under the battery and whiffs of hot glycol. I lifted the overflow hose from its usual spot and got rewarded by FL22 vapour that'd condensed in it. It'd been dumping onto the radiator fan so the evidence was scattered to the wind and the overflow itself always seemed clean and dry and residue free.


Engine seems to have survived. Starts and idles fine. Usual condensate smoke clears up once the engine's hot.


(EDIT: And this may be in the wrong forum)

 

You clearly aren't in the US, but there might be a similar option where you are:

Go to your FLAPS of choice (Friendly Local Auto Parts Store), and rent a cooling system pressure testing kit.

Then you have a choice to make: either fill it up or drain it. If you think the leak is minor and not somewhere super high up, leave the coolant in it. If it's a bad leak (doesn't sound like it), it might be quicker to just drain it. If the full method doesn't work, you'll be draining it anyway, and you already have it full, so unless you know it's bad, that's where you want to start.

Hook up the tester, warm up the car, then quickly (so you don't lose too much heat) pump up the pressure to system max, or however high you can get it, and look/listen. With the engine off, you'll be less hesitant to stick squishy body parts down in places that you might not otherwise with bits of metal twirling about. You'll also be able to hear hisses and drips. Drips may take some time, so be prepared to wait and maybe even pump it up a few times. This will most likely get you where you need to start. Find your leak(s), and figure out the appropriate remedy. A trick to help find hisses is to get a length of hose; .5m or a little less. Stick one end in your ear, and use the other to "hear around" various possible leak sources. This stage is most likely to result in visible leaks, but hisses aren't out of the question, and finding them now can save you some steps.

If that doesn't provide you the necessary information, get the engine warm (without causing damage), then quickly drain the coolant, get a spray bottle full of water with lots of dish soap (you want big thick bubbles), and even a little glycerine if you have it (even bigger, bubbles). You'll want all of this to hand before you start for obvious reasons. Spritz everywhere there could possibly be a leak. If there are too many places, you'll have to work in stages, and may be refilling/rewarming the engine as you go. Speed is your friend, but be careful so you don't miss things.

If that STILL doesn't reveal the source of your leak, it's in the block and rebuild time. If you're like me though, you want to be sure. You'll need a helper for this phase. So fill it back up with coolant (which you're hopefully reusing since you've gone through a handful of refills to this point). Pull/prepare to pull everything you practically can between you and the easiest/closest removable joint of either intake or exhaust. Preferably both, and closer to the block is better. Also remove your spark plugs. It's best to gain access to each rotor face as best you can. Priorities are exhaust manifold, spark plugs, and intake in order of likelihood. Get it up to temp, then remove what you figured was easiest to remove/highest priority quickly without losing more heat than necessary (thermal expansion may be a factor), pressurize the system, and stick your hose down whatever hole(s) you've exposed and listen. Your buddy will likely need to turn the engine over by hand. Listen around between the rotors, and you should hear your leak pretty handily if you haven't found it to this point. Bonus: your top end is already partially torn down for removal!

 

Thanks for the comprehensive reply, . but I found it. The hose had been pointed at the fan. I noticed steam from the engine bay - searched for twhere it was coming from and pulled the hose up out of its pit. It has never been wet previously, and never once shown a stain.

 

Check the underside of the hood, you may find your splatter marks there. But yep so it was getting past the pressure cap. Could be as simple as a bad cap, but potentially the cap worked as advertised and the system ran over pressure from some unwelcome gasses.

I would do a chemical block test to see if there's exhaust in the coolant to confirm or eliminate that line of investigation.

 

might need to replace the coolant bottle; known to leak with age and not hold a good seal with the radiator cap. To me that’s pretty much your pic above is showing.

you might consider upgrading to an aluminum version, only thing is the coolant level is not readily visible.
.

 

6 month update.

Swapped the bottle cap. Kept leaking for a few weeks. It's settled down since. Had overfilled it a little bit when I refilled it so it would burp a little. Just keeping an eye on it - it still stinks of coolant when hot but it's not loosing any.

Engine has run about 6k since - it seems to have survived. Scrammed it before it began to properly boil - it probably stayed mostly cooled the entire time.


Oil is dry. No smoke in exhaust. Exhaust itself has rusted through somewhere. Needs a new manifold maybe.


It needs more money than I can spare to patch it up. Mostly rust, sticky valves and other shenanigans. Engine - touch wood - seems to be fine.