Not sure why this thread is called block work - I've only just noticed, when I saw it I was hoping it was someone on about filling the water jackets for drag racing - shame.
I've never known any HDi/XUD mix it's oil/coolant - this is because the cylinder pressures are always very high, it'll just push combustion gas into the water jacket instead if the head gasket is breached, there isn't anywhere for the oil and water to mix - if the leak manages to get anywhere near the high pressure oil ascent circuit or descent circuit, you can guarantee the engine won't even attempt to start by that point it'll have so little compression. If it's leaking combustion gas into the coolant and pressurizing - that is a head gasket failure, whether that is due to the gasket itself failing due to age or the head bolts undergoing elastic/plastic deformation and allowing gas past - not sure.
"Sounds like it has a rev limiter" isn't particularly great diagnosis in honesty... You'll know you have it if you turn up the boost (therefore exhaust pressure is higher...) - at higher RPM the engine will fall flat on it's arse, exhaust go very loud and it'll smoke like hell. If you keep pressing through it, you're in danger of damage. Measure exhaust manifold pressure, it's the only way you'll ever know what's going on and whether you need the springs.
Infact - here is exactly what happens when your valve springs are too weak (or in this case - trying to get too much boost out a tiny turbo at high RPM): https://www.306oc.co.uk/forum/showthread.php?tid=35661
Notice the dyno curve... Too much juice at high RPM causing high EMP (probably too late EOI also) valve springs float, power goes down, pwarp, keep going and it'll snap a rocker.
I've never known any HDi/XUD mix it's oil/coolant - this is because the cylinder pressures are always very high, it'll just push combustion gas into the water jacket instead if the head gasket is breached, there isn't anywhere for the oil and water to mix - if the leak manages to get anywhere near the high pressure oil ascent circuit or descent circuit, you can guarantee the engine won't even attempt to start by that point it'll have so little compression. If it's leaking combustion gas into the coolant and pressurizing - that is a head gasket failure, whether that is due to the gasket itself failing due to age or the head bolts undergoing elastic/plastic deformation and allowing gas past - not sure.
"Sounds like it has a rev limiter" isn't particularly great diagnosis in honesty... You'll know you have it if you turn up the boost (therefore exhaust pressure is higher...) - at higher RPM the engine will fall flat on it's arse, exhaust go very loud and it'll smoke like hell. If you keep pressing through it, you're in danger of damage. Measure exhaust manifold pressure, it's the only way you'll ever know what's going on and whether you need the springs.
Infact - here is exactly what happens when your valve springs are too weak (or in this case - trying to get too much boost out a tiny turbo at high RPM): https://www.306oc.co.uk/forum/showthread.php?tid=35661
Notice the dyno curve... Too much juice at high RPM causing high EMP (probably too late EOI also) valve springs float, power goes down, pwarp, keep going and it'll snap a rocker.
