Pressurising coolant tank

I noticed on the last run out when I parked up the coolant expansion cap was showing signs of some dribbles and leaks. Now this has happened before and it was the expansion cap seal that had gone so a replacement cap was bought and no leaks since. I would guesstimate 2-3000 miles since at least.

Checked the car some time later when cool and lots of pressure behind the cap such that some coolant came out. However there is no discernible drop in coolant level. Oil level also fine.

I started the car up a week later and it sounded like it was running on 3 cylinders so switched off immediately. I checked HT leads, had no tools to speak of with me at the time so limited checks were possible. Checked the air intake into the carbon box, filter still looks good (was given a clean at the last check also). The plugs were pulled just before the last trip too and gaps checked, some minor adjustment to spec. All plugs looked a good colour, no oil or fouling. Also replaced the coil at that time so my hope was that maybe it’s the coil or a sparkplug issue but sounds like it could be with the pressurising coolant more serious.

Car seemed to run fine on the last run so a little perplexed. It was a pretty steady run too.

Compression test worthwhile I suppose. Any tips pointers or funding suggestions for what sounds like an expensive repair?!

could be worth doing a sniff test on the coolant to see if the head gasket is passing. i had a gasket failure which even of the car was left overnight the expansion bottle would remain pressurised

It may be worth checking the Thermostat operation. (dip it into boiling water to see if it fully opens).
As the coolant level needs to be dropped to remove the thermostat, it may be beneficial to flush the system through and replace the coolant at the same time. (8 litres if memory serves)

Hope the solution is simple, quick & minor.

Have you topped up the coolant recently? They all seem to find their own level and can ‘spit’ if they are filled above this level.

You could do a sniff test on the coolant and check for mayo if it puts your mind at rest. If it was running on three cylinders but has now fixed itself, it could also be the coil pack, ignition lead or even injector. As you mentioned unplugging leads that may have inadvertently fixed it, so you could just buy a new set of leads and a coil pack if you can’t find anything else.

Okay so pulled the plugs and they are all fouled with excess fuel.

Cleaned them up thoroughly but the vacuum hoses are also fouled, so removed all of those including T-pieces and gave them a clean with carb cleaner.

Started her up and running on all four. Sounded like a good run would do it good.

Switched off after a few minutes of holding at 2000rpm, letting it drop to normal idle at around 1250rpm and some gentle revving. Seemed okay. Sounded as it should though perhaps some slight spluttering on gentle blips.

Had a cuppa and thought a little run would be good to test her out. Started the old girl up and misfire again, sounding like running on three, switched off.

So I did swap the coil back for the original the day before all this happened. Perhaps the culprit?

Seems like massive overfueling. Perhaps a stuck open injector?

I plan to send away my original injectors for cleaning and refit those. I will also refit the coil pack that was on previously.

However, oil/fuel in the vacuum hoses. Is that possibly caused by an inlet manifold leak somewhere?

Quite a few things there, but it’s easy to start noticing things and going down rabbit holes in the wrong direction!

You mentioned oil/fuel in the vacuum hoses - have you checked the FPR for damage/leaks? A small tear in the diaphragm could allow fuel in the pipework and make it misbehave. If your emissions equipment is still connected, you may get some oil/water in the intake systems, but I’d be surprised if it was filling the vacuum tubing, as it’s only supposed to inject under part-load conditions to burn it off. Could always blank it off though, if you wanted.

If you think all the plugs are too wet, then it’s probably not going to be leads, but it wouldn’t hurt to replace the coil pack. Strange that it’s just not a misfire on one cylinder, so could be worth plugging in an OBD and checking all the parameters to see if something jumps out (vacuum, TPS, IACV, advance etc.)?

Let me know if you need a second pair of eyes :+1:

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Really appreciate that Craig thank you, just back from holiday so not been back to look any further. I’ll PM you to try arrange a time to maybe look at things. FPR sounds a good shout.

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So by way of an update, swapped the coil pack, cleaned the plugs and I have myself a sweet sounding Exige again. T’was a little grumpy on first start then all good again, a short run and going well, I missed that feeling so much the last few weeks, special little cars these :grin:

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