Spectacular Failure!

[steve@cornwall 100]

Coming home in the cti today I had a spectacular moment. It has recently been overheating, but today was hovering around the two thirds mark on guage when I decided to overtake a lorry. Just past the cab when the stop light came on so dropped the clutch- as heading down a big hill- with throttle not on at all the revs were bouncing off the limiter- so I turned the key off- still bouncing off the limiter!!!! Then came the massive bang and an enormous fog cloud behind the car But at least it cut out.

Coasted to a halt at the bottom of the hill and up onto a curb- at least only 1.5 miles from home so was considdering recovery options. turned the key, expecting terrible noises and little else and it sprung to life!!!!

Lots of steam,though. Anyone think this contributed to my overheating?

 

[Rob_the_Sparky 9]

No, but certainly contributed to the steam!

[smckeown 1]

doesnt that indicate pressure build up ?

[Rob_the_Sparky 9]

Or a severely cracked and perished hose. Not sure you can read much more into it than that..

[nick 3]

So why was it bouncing off the limiter?

 

Nick

[steve@cornwall 100]

So why was it bouncing off the limiter?

 

Nick

 

and wouldn't switch off?-bloody weird!

[Owain1602 0]

You can look more in to it. Generally it indicates too much pressure in the cooling system and the weakest part will blow first so maybe your hose was perishing a little. But what you need to find out is, if you have too much pressure in the system. More often than not its because of head-gasket failure but it could be other things.

Get a hose and see how quick the cooling system pressurises.

[mbayley77 0]

Steve, I know where thers a spare hose on a 205 not too far from the cti

 

Bad luck though and strange why it should be pressurising like that. Maybe a compression test may tell you some more?

[jonah 1]

and wouldn't switch off?-bloody weird!

Something very strange going on there!

 

Stop light comes on which means it's overheated (or oil pressure is low), so you:

Dip the clutch, which removes external drive from the engine

Lift off the throttle, which cuts off its air supply

Turn the key to off, which kills the spark and shuts off the fuel injection

 

And yet it was still revving its nuts off!? How is that even remotely possible???

 

Only thing left to burn is the engine oil... but there would have to be something very seriously wrong for that to happen!

[steve@cornwall 100]

Steve, I know where thers a spare hose on a 205 not too far from the cti

 

Bad luck though and strange why it should be pressurising like that. Maybe a compression test may tell you some more?

 

In truth, it's been waiting to happen- but if the engine dies I'll get on with fitting the mi in the garage! lucky I was so close to home, though, it drove home in that state so if the h/g wasn't fubar this morning I won't take bets on it being any good tonight! (another project bottom-end?) Still reckon it's worth a hose,some coolant and a good rag up the road,though. Starts and stops fine now so I can only assume that an engine bay full of steam had something to do with the ridiculous running-on problems, maybe massively hot cylinders and a shorted temp sender? (pre-ignition and open injectors) or maybe i've been up too long and am having a weird waking dream!!!!

[pugrallye 0]

more than likely a weak hose, i blew one today too, but been waiting for it to go for over a year now, there is no head scratching really 10+ year old car... old and dodgy hoses, as for you car revving its nuts off, sounds like throttle got stuck on, either a cable or a gunked up throttle body, or, you have a clutch problem as drive should have been disengaged immediately you put clutch in

[KRISKARRERA 2 1 Cars]

Did you not take it out of gear and leave it in neutral?

[steve@cornwall 100]

Did you not take it out of gear and leave it in neutral?

 

 

Just dipped clutch, which is working fine, was in fourth gear at about 60mph- so no relation to 7000 rpm!(and wasn't at full throttle anyway). Drove home fine after stopping and cooling a little. Just thinking that as the hose burst on a curve it may have been collapsing and restricting water flow when hot. Now going out to fit a new hose so fingers crossed.

[jonah 1]

I can only assume that an engine bay full of steam had something to do with the ridiculous running-on problems, maybe massively hot cylinders and a shorted temp sender? (pre-ignition and open injectors)

Heat in the cylinders can cause a carb'd car to run on because the carb will carry on supplying fuel, but not at 7000rpm when the throttle's shut! But we're talking about an EFI engine here, so as soon as you turn off the key the fuel supply is INSTANTLY cut, shorted temp sender or not. Anyway I thought the running-on problem happened before the hose popped?

 

Very very weird!

[steve@cornwall 100]

Heat in the cylinders can cause a carb'd car to run on because the carb will carry on supplying fuel, but not at 7000rpm when the throttle's shut! But we're talking about an EFI engine here, so as soon as you turn off the key the fuel supply is INSTANTLY cut, shorted temp sender or not. Anyway I thought the running-on problem happened before the hose popped?

 

Very very weird!

 

 

Before hose popped, but not before first steam!

 

Hose replaced and coolant (neat water for now) added and ragged for a few miles still getting too hot for a car with no stat and fan wired to ignition!!!.

 

Bought a gunson's compression tester and tested

 

200 - 185 - 230 - (checked and double checked) 230

 

oiled bores shows

 

220 - 220- 230 - 230 I'll trust the differences between bores- but not the reading overall.

 

Starts/ drives great and idles at a steady 800 ish

 

MI TIME methinks

[jonah 1]

fan wired to ignition!!!.

There's a clue

 

Is the thermoswitch still connected?

 

If so, then whenever the thermoswitch turns on, your extra connection will work in reverse and the fan switch will power up the ignition circuit! So turning off the key would have no effect.

 

So that would explain that part... but still not why it was revving to 7k with your foot off the throttle...

[jim21070 2]

Hose replaced and coolant (neat water for now) added and ragged for a few miles still getting too hot for a car with no stat and fan wired to ignition!!!.

 

Bought a gunson's compression tester and tested

 

200 - 185 - 230 - (checked and double checked) 230

 

oiled bores shows

 

220 - 220- 230 - 230 I'll trust the differences between bores- but not the reading overall.

 

Starts/ drives great and idles at a steady 800 ish

 

MI TIME methinks

 

At the risk of stating the bleedin' obvious, something does not add up here. No stat and it still gets too hot after a short drive. Compression checks seem to indicate HG is OK.

 

I reckon you have a blockage or a severe restriction somewhere in the cooling system somewhere. I have a feeling in the back of my mind that you've already been here and swapped the rad, which would be a prime suspect.

 

The only things I can think of now is that it is the HG failing under compression pressure or your internal engine waterways have become badly silted up. I was once surprised to see just how much crap and rubbish can collect in the water passages around the bottom of the liners when the coolant has been neglected. Also, the alloy corrodes like hell if plain water has been used for any length of time and all that corrosion can block things up.

 

It is a very remote chance but the water pump impeller could have corroded its blades off but to do this without leaks would be almost on a par with a lottery win. Clutching at straws now

 

Despite the HG appearing Ok, I reckon it's a head-off job now, just to determine just what the hell is going on as something sure is. An engine in fine fettle with a good rad runs very cool normally.

 

This is getting interesting. keep us posted...

[steve@cornwall 100]

Jonah- Nice one! one bodge to remove tomorrow! Seemed such a good idea at the time. As it's wired to slow speed fan it either cut in very late- or my guage is telling little porkies!

 

Jim- When cold and ticking over the top hose pressure rises with revs until engine is hot when it is pressurised constantly, so don't suspect the pump. All hoses heat and heater works fine so drastic blockage seems unlikely.

Strange thing is There's no normal overheating smell or cooling down "ticking"- doesn't seem to be boiling either. (Did boil once, the first major overheating at silly speeds on a hot day, but may have been low on cooolant anyway) I may just change the sender and see what the guage says.

 

Yes this does follow an earlier post and the rad has been changed for a known good one.

 

Nightly bad thought- what's the symptoms for a cracked liner? I do have a pronounced "single rythmic tick"

 

If the problem isn't solved by the time the engine comes out for conversion, i'll strip it and investigate,however I'd like to have a resonably good idea that the cooling system is o.k as rad and several pipes etc will be used on the MI

 

Cheers for the input guys- making progress, I think

[Guest BrainFluid]

If the engine was still running with the spark killed the cylinders must be so hot that they were igniting either petrol or oil...

 

unlikely to be either petrol or oil really, unless the fuel system is fecked and letting it in or somehow the oil was getting in. I havent heard you mention the oil levels after all this?

 

Like jim says maybe the gasket is failing under compression, you would expect to see the symptoms of this though. Are they any? one of the cylinder test showed a noticably lower reading.

 

Can excessive heat affect the fuel system?

 

But hey, I'm new to petrol engines so I could be talking bollox, just trying to help.

[jonah 1]

If the engine was still running with the spark killed the cylinders must be so hot that they were igniting either petrol or oil...

Catch up We've got to the bottom of that one... fan circuit was wired to ignition so the ignition and injection system carried on running when it was turned off at the key.

 

As for the head gasket failing under compression... I think that's exactly what's happening (or maybe a crack opening up in a liner or the head, but you'll never know which without taking it apart). HG went on my Pug a couple of years back and it did similar things, only less severe. At idle or revving the engine unloaded, there were no symptoms at all. Compression test showed nothing, couldn't feel any pressure building up in the cooling system when the car was stationary, and even a sniffer test came up negative. But, whenever I thrashed the engine hard, it would erupt coolant out of the header tank past the pressure cap. Despite this, the temp gauge was always bang on normal. When I took the head off I found evidence of a blow between cyls 2&3 and the water jacket.

 

In your case the blow is obviously worse, and you can feel the coolant system pressurising even with the engine unloaded. I suspect the overheating is caused by the combustion gases getting into the cooling system and causing an air lock. That might also cause the SAD (cold start device) to go cold because hot coolant isn't being pumped past it, so could explain some of the high revving.

 

Comp test doesn't show a drop in compression but it would take a very severe blow to be measurable on a comp test. If anything, the abnormally high readings could be due to coolant pooling in those two cylinders after you've turned the engine off...

Edited September 13, 2006 by jonah

[steve@cornwall 100]

I think I know why the revs shot up without the throttle!!!- Took a good look at the layout of components when fitting a new temp sender. Top hose must have blown up like a bloody great balloon and simply pushed the throttle mech. wide open until the hose burst!

 

Bubbles in expansion tank on wide throttle;- = fubar h/g, right?

 

Thanks for the input,guys- never had so much fun atfer f*cking a h/g!

Edited September 13, 2006 by steve@cornwall

[jim21070 2]

Bubbles in expansion tank on wide throttle;- = fubar h/g, right?

 

Certainly looks that way I'm sorry to say... Time to get the spanners out..

 

Amazing a top hose can blow up to such a size to jam the throttle. Well deduced

 

Thanks for posting this , I get so frustrated when a thread is left dangling because the original poster does not conclude it with findings and letting us know if the advice offerd worked or helpled

[PumaRacing 2]

Something very strange going on there!

 

Stop light comes on which means it's overheated (or oil pressure is low), so you:

Dip the clutch, which removes external drive from the engine

Lift off the throttle, which cuts off its air supply

Turn the key to off, which kills the spark and shuts off the fuel injection

 

And yet it was still revving its nuts off!? How is that even remotely possible???

 

It's obvious as there is only one way a petrol engine can rev with the throttle shut. The throttle wasn't shut. The pedal might not have been down but sure as eggs is eggs the butterfly was jammed open.

 

Diesels have no throttle so they will rev on their own engine oil if enough of it gets into the cylinders.

[Guest BrainFluid]

Catch up We've got to the bottom of that one... fan circuit was wired to ignition so the ignition and injection system carried on running when it was turned off at the key.

 

Eeps! Sorry about that.

 

I'll just go and stand in the corner for a while with my dunce cap on.

[steve@cornwall 100]

Certainly looks that way I'm sorry to say... Time to get the spanners out..

 

Amazing a top hose can blow up to such a size to jam the throttle. Well deduced

 

Thanks for posting this , I get so frustrated when a thread is left dangling because the original poster does not conclude it with findings and letting us know if the advice offerd worked or helpled

 

Going to organise some tim off work to fit MI ! I'll lift the head and let you know about the gasket in due course!.

 

And ditto about dangling threads. I find all ideas useful- If you don't know what's wrong it can't hurt to check anything and everything along the way- I'm also often overlooking the obvious too!

 

Is there a post icon that can be added to a successful thread?