[Mk2] [Turbo] Oh dear, overheating.. cracked block?

[RyanRs]

Gave the car a good hard pull on the motorway today when the coolant temp gauge suddenly shot right up and the ecu triggered limp mode. nursed it back home as the gauge was fluctuating between half way and off the scale, i had to stop several times to allow it too cool down.

It now appears there is no coolant in the system! the expansion bottle pipe was bubbling like crazy and all the coolant pipes are rock solid -but with air i would say. Cabin heater is blowing cold now too. The expansion bottle did overflow bigtime.

Now, if i have cracked the block, i would get white smoke from the exhaust wouldn't i? and going by the rate at which this deteriorated (ie from full topped up coolant down to practically nothing) there should be a LOT of white smoke surely? there is no split pipes etc. I did notice my coolant expansion bottle was empty this morning and i did fill it up prior to going out today -bear in mind i use this car like once a month max, so its not as if i check these things on a daily basis. Now i wonder if this is just a case of the air in the system thats been sucked in from the bottle being empty has caused over-pressurization and coughed out all the coolant?

any suggestions.

Btw, for anyone who dont know its a rev3 custom built 570bhp so may be a little different the usual oem reasons.

thanks.

[ashley]

Hope it ain't so mate...

When I did my block I didn't notice any smoke out the back, but similar symptoms to you...it overheated the first couple of times only on boost, but shortly afterwards every time I got on the throttle the temp would rise. I refilled the coolant several times to limp it home, and had to keep stopping to let it cool down.

Probably not helpful, good luck- hope it's something more easily fixed like a split coolant pipe or head gasket

[MartinF]

Check your rad cap first.

It could be something as simple as that and hope that you haven't suffered any damage.

[bobhatton]

Let’s look at this.

A Rev 3 with 8.5:1 runs what 0.8 bar boost on road fuel.
You are running 8.3:1, but I am not sure that is right with a 1mm gasket, and just on 2 bar of boost on road fuel.

Is that telling you anything?

[RyanRs]

Let’s look at this.

A Rev 3 with 8.5:1 runs what 0.8 bar boost on road fuel.
You are running 8.3:1, but I am not sure that is right with a 1mm gasket, and just on 2 bar of boost on road fuel.

Is that telling you anything?

8.4:1

no, what are you getting at?

[bobhatton]

To be able to run 2 bar boost you should be around 7.0:1 compression ratio.

To overcome the fact you are at 8.4:1 the ignition advance will have had to be retarded from its correct setting by about 20 deg I would think to stop detonation.

This will mean the maximum combustion pressure instead of being in the cylinder head is now going to be about 35 deg atdc way down in the cylinder at a place that is not designed for that pressure, so will crack the cylinder bore.

I hope I am wrong but its all pointing to a cracked cylinder

[dawesy]

Personally I'd refil and bleed the system, check the cap and see. When mine went it would drive fine off boost but on boost it would overheat. As soo. As I let off the temp slowly came down. Fingers crossed bud

[Moo]

Not good dude Hope it's nothing serious.

[Kongaroo]

Have you tried pressurising the coolant system with a pressure tester and checking for leaks?

I recently had a crack in one of the coolant hoses for the MX5 that would only leak under a fair bit of pressure so it didn't show up when just starting up and idling the car.

When Peter pressurised the coolant system to about 1 bar it showed up as a mini pinhole vapour leak so didn't leave any puddles under the car but caused 50% of my coolant to be lost over just 3 commuting days.

I was really relieved as after having had a cracked block on the MR2 before I was already fearing the worst

[RyanRs]

To be able to run 2 bar boost you should be around 7.0:1 compression ratio.

To overcome the fact you are at 8.4:1 the ignition advance will have had to be retarded from its correct setting by about 20 deg I would think to stop detonation.

This will mean the maximum combustion pressure instead of being in the cylinder head is now going to be about 35 deg atdc way down in the cylinder at a place that is not designed for that pressure, so will crack the cylinder bore.

I hope I am wrong but its all pointing to a cracked cylinder

Well this was the compression ratio recommended by Tony (used to be at rogue) he built the bottom end and afik he was also a race car engine builder. Also, doesn't the limiting boost also depend on the turbo used? as 2bar from a 3071 with give much hotter IAT's than a GT3582r -of which i am using.

When it was running 1.6 bar it had ignition advance , dont know how much but it was advanced. At 2 bar Ryan had to zero the ignition advance due to 52'c IAT due to the IC being inefficient. There was no ignition retarding tho.

I just pulled the plugs, all piston crowns are dry, well light damp coating thats always seemed to be there; plugs are dry but no4 plug had burnt off a slight bit of its ground electrode. Im guessing this is due to a bit of det as the engine overheated. All plugs was black with overfuel soot.

[Mike N]

When mine cracked I couldn't see anything until the head was off. The crack was vertical around 2 inches long on number 2 pot.

The car also ran perfect in all respects other than when using 1.5bar on full chat in 3rd gear onward, at which point almost all of the coolant was blown out of the filler cap! The engine then took 3/4 of an hour to cool down.

[RyanRs]

Well, just thought I'd write what the problem was, hhopefully save someone a panic attack and migraine someday.. Basically my coolant expansion bottle was too small and each time Idrove the car it would fill the bottle and overflow ever so slightly, then when it cooled down again it would suck all tthe coolant back in + a little bit of air as Obv some of the coast had overflowed. Over time this happened a few times until there was too much air in the system which caused the massive overheating . I have thoroughly bled the system, replaced 4 litres of missing coolant! And took it for a run.. Never went above half way on the temp gauge.

Thank gawd for that!

[Peter Gidden]

Basically my coolant expansion bottle was too small

Why do you have a non-standard expansion bottle?

[Kongaroo]

Ryan can you put up a link to the expansion bottle so we know which one to avoid?

[dawesy]

might be a dodgy rad cap as well

[ashley]

Well, just thought I'd write what the problem was, hhopefully save someone a panic attack and migraine someday.. Basically my coolant expansion bottle was too small and each time Idrove the car it would fill the bottle and overflow ever so slightly, then when it cooled down again it would suck all tthe coolant back in + a little bit of air as Obv some of the coast had overflowed. Over time this happened a few times until there was too much air in the system which caused the massive overheating . I have thoroughly bled the system, replaced 4 litres of missing coolant! And took it for a run.. Never went above half way on the temp gauge.

Thank gawd for that!

Fantastic result if that's right mate

How did you work out this is what was happening?

When you took it for a run did you drive on boost?

Relieved for you

[RyanRs]

Ryan can you put up a link to the expansion bottle so we know which one to avoid?

Ahhh Ahahaaa ok, i'm gonna get taken to the cleaners for this






Yea I kinda been intending to make a custom one for quite a while but just have never got around to doing it. This was supposed to be a temporary fix.. The bottle was large enough but as the super hot coolant filled the bottle each time, the bottle shrank more and more.. It's litterally 1/2 the size of when I first put it in!

I'm not using the oem bottle as it's ugly and with the missus minimal look of my engine bay, it had to go. An ally one will go in the boot soon as I make it.

[ashley]

[RyanRs]

Well, just thought I'd write what the problem was, hhopefully save someone a panic attack and migraine someday.. Basically my coolant expansion bottle was too small and each time Idrove the car it would fill the bottle and overflow ever so slightly, then when it cooled down again it would suck all tthe coolant back in + a little bit of air as Obv some of the coast had overflowed. Over time this happened a few times until there was too much air in the system which caused the massive overheating . I have thoroughly bled the system, replaced 4 litres of missing coolant! And took it for a run.. Never went above half way on the temp gauge.

Thank gawd for that!

Fantastic result if that's right mate

How did you work out this is what was happening?

When you took it for a run did you drive on boost?

Relieved for you

Basically, just stopped and thought about it for a minute, given the bottle I used and how small it had shrunk, and the fact I found it empty on about 5 occasions! Tbh as it was not overheating previously, I just assumed there was the perfect amount of coolant in the system, ie exactly the same amount of coolant expanded in the bottle was returned when cool, didn't for a second think I might be losing some each time. Obv the more air in the system the more pressure and the more coolant was lost each time.

I tool the car for 5 mile run and give it a couple of 2nd, 3rd pulls to redline and temp gauge stayed nicely just below half way, had the big spal engine lid fans off for it also. Seems all is good! .

[dawesy]

yeah defo not good, glad it was something simple.
stock one isnt that obvious, how empty is your bay?