Water-cooled engine - odd symptoms

[mark_in_manchester]

Hi Folks

I have a Daihatsu Charade engine in a Ural. It starts and runs well, but I have long dealt with annoying cooling issues. I'm a little paranoid about this, as I have a number of spare heads which are cracked between the valve seats. These engines are known to do this, especially due to cooling failure.

The cooling system is set up with a radiator *not* at the top of the system, with a (recently replaced) pressure cap which passes expanded coolant to an expansion bottle. On cooling down, this cap allows the engine to draw coolant back in. It is plumbed with a 4-500mm length of 22mm copper pipe along / over the top of the cyl head, which provides something of a coolant reservoir / header. At the rear end of this header is an extension which terminates in a brass 'pot' with a float valve in it, which would normally be used to bleed air from a pressurised domestic heating system. I remove the lid to use this as my filler, since it is at the highest point.

The 'odd symptoms' are as follows. When I run the bike, the volume of fluid in the expansion bottle increases as expected. When I let it cool, it appears not to pull coolant back in. When I check at my 'filler cap', I have to top up with up to 250ml of water each time I start the bike.

Perhaps I have a small leak, through which I can pull air back into the system on cooling. But...it doesn't appear to drip water when running. Perhaps this evaporates off and is not therefore visible. Sometimes the water level appears to drop quite fast, even before engine has warmed, let alone cooled. Perhaps this is due to air pockets in the system. At least it runs without blowing water everywhere with the filler cap removed, so radical pressurisation (a *really* cracked head) does not appear to be the fault.

So - any ideas, either on causes, or on tests to try, to narrow down the problem? I guess I could try to measure the pressure in the system somehow, and see if the cap blows off at the correct value, for a start.

cheers

Mark

[alexanderfoti]

I am no expert, but I would say if you are loosing water, and its not visible leaking anywhere, then you are burning it.

I know you can get a kit that detects the presence of collant in the exhaust gas, maybe thats a good place to start?

[mark_in_manchester]

Well...I *think* I am adding water which is ending up in the expansion bottle. Certainly when I am lazy and do not use my big syringe to pull it out of the bottle and inject back into filler cap (yes, I really do this) but just pour in to the top from a jug, then sooner or later expansion bottle overflows. I guess I could attempt an experiment where I measure coolant volume in bottle, with system full, engine cold, then run it for a while and at least see if volume is conserved. So good - thought process helps already! More ideas?

[Eddy Wane]

There is definitely one thing that should not happen and that is that the expansion bottle should not overflow and retain the water. As the water cools it should be drawn back out of the bottle down to the fill mark if you have one.
Can you post a drawing of how you have plumbed it as this might help other members to work out your problem. I am right in thinking you have emulated the pipework from the Charade.
On a lighter note my mate re commissioned an old engine and when he changed the thermostat he fond the remains of a mouse in it.

[gilburton]

Is your cap like this Suzuki Jimny??
They are not just a simple cap and employ a couple of valves.
Another problem that was found was old hoses collapsing under vacuum and not letting the water back in.
Just a thought??

http://www.bigjimny.com/index.php/forum ... blem#96111

[mark_in_manchester]

I use an 'old' mini radiator, with a cap like this

http://www.ebay.co.uk/itm/10-lb-Long-Re ... 257dccb698

It blows past at a certain pressure (I need to check which cap I have) via the large washer, and sucks back via the smaller brass valve in the middle which is more lightly sprung in the opposite direction to the former.

[gilburton]

I'm only going from memory but didn't later cars just have a cap that stopped the water escaping but didn't stop the flow on the radiator and they had the proper expansion cap on the expansion bottle not the radiator??
Don't think the mini was designed for an overflow bottle so possibly if you can find a reservoir with a pressure cap and remove the spring bit from the radiator so that water doesn't spill out but it can flow freely between reservoir/radiator??
Even so if water is blowing past the cap are you overheating??

[BertTrack]

Sounds like you have the same system my "ktm" coolant system has. (on the track)

The pressure cap acts with over pressure and under pressure. Any pressure over x and water will go to the reservoir. Any pressure under y (below atmosphere) will allow liquid to stream back.

The problem you have is the central heating de-air unit. This will allow air back into the system when there is a pressure below atmosphere.

So you fill up the reservoir upon heating the engine. And when it cools it will suck back air in from the de-air unit. The only way to make this work is to have an expansion system. Which always keeps a positive pressure on the coolant.

Or put a valve under the de-air unit so you can only use it to refill and bleed off after filling. But shut it during the first run.

My regulated pressure cap actually has the pressure on it. Opens @ 0.5 and @ -0.15 or so. Bar.

[mark_in_manchester]

Bert - I do have the same system as you - thanks for writing its operation clearly. But I should have clarified that the central-heating air bleed is kept screwed shut at all times (with a small brass cap about the size of that which covers a tyre valve), apart from the odd occasion when engine is hot and I want to bleed the air off - then I loosen this cap, and it hisses until either all gas escapes and liquid closes float valve underneath in the pot, or it runs out of pressure before liquid reaches this far.

Of course this small cap may leak air in a little, and prevent system drawing coolant back in from (open top - 1 bar!) expansion bottle. But this leak could be anywhere else, too.

I think I might try to pressurise the cold system with a little air, measuring the pressure the radiator cap blows off at, looking for obvious leaks, and checking it can hold a static pressure. I guess system should be sealed, and therefore able to hold a pressure (just under cap blow-off) indefinitely?

[tappy]

Well...I *think* I am adding water which is ending up in the expansion bottle. Certainly when I am lazy and do not use my big syringe to pull it out of the bottle and inject back into filler cap (yes, I really do this) but just pour in to the top from a jug, then sooner or later expansion bottle overflows. I guess I could attempt an experiment where I measure coolant volume in bottle, with system full, engine cold, then run it for a while and at least see if volume is conserved. So good - thought process helps already! More ideas?

SOOO, you're not losing water.
Does the hose that goes to the expansion bottle have its end submerged below the level of coolant in the expansion bottle? If not - it could never draw water back in anyway...

[BertTrack]

Bert -

Good idea testing it!

In the same way you can test if the cap also opens on vacuum by putting very little pressure on the line from the cap to the reservoir. If the opening pressure for vacuum is too hight chances are any sort of leak (i never trust that cap on top of central heating de-air systems) will .. well you know. hope you find out what's venting.

[mark_in_manchester]

Oh dear, Well, things have progressed a little.

I fitted pushbike tyre valve to cooling system, and pumped a little with bike pump. Water ejected from expansion bottle tube immediately at only just over atm pressure. Seal was no good.

So I added extra rubber washer carefully cut around central negative-pressure valve in rad cap, so as to only raise blow-off pressure for positive pressure situation. Now blows off after a few strokes with bike pump (maybe 15psi) - seems ok. System hold pressure for a while, and no other leaks evident in pipework when under pressure.

Now when running. System pressurises almost immediately. With a full expansion bottle it foams like hell and wets my leg - especially under heavy load. Gets a bit better when engine warms up. Lots of gas collects in system filler at highest point - central heating blow-off described before.

My guess is that head (like my 2 spares not attached to engines) is cracked between valve seats. Bugger. Still runs fine, starts fine, ticks over well...may be some time before I bring myself to fit spare engine, which (who knows) may be entirely buggered too. I'll kick myself if it stops working somewhere remote, which sound quite likely to me

1) What do you think?
2) Anyone have experience with having alloy head welded? Valve seats are in the way, and I think would need to come out before repair, and be replaced. Sounds like ££££....

[Bert in Weesp]

Hoi,

Some years ago as a nici DIY job I partly overhauled such a engine, oversize pistons, valve slider things etcetera. Mine cyl head at that time also had ( to my opinion ) big cracks between the valve seats, but the garage was not impressed at all, told me to put it together as was and see what happened...Engine ran very fine without a single drop flid loss, so I think that your cracked heads may be fine.

Your running engine to me souds very much like a blown head gasket, I had 2 in 14 years and 392.000 km in my charade car, somehow the inside of the steel rings wear out. But at the second head gasket wich was at about 320.000 km ( No, I did not help it a little by making a device to increase turbo pressure to 1.0 bar wich made the machine go like a pocket rocket) .

Bert

[mark_in_manchester]

Bert -

I'm very grateful for you taking the time to post your experiences (and taking the time to register on this forum, to tell me!). Isn't the internet a strange thing - NL to UK hugely specific technical advice between total strangers who will never meet. So this is encouraging, and for the price of a head gasket...why not. Did you re-use the bolts to hold the head down, or buy new ones? Despite building this bike, and despite years and years of taking petrol engines apart, this diesel is to me a 'black box' and I am a little scared of high torque head bolts and making a 'pigs ear' of this. Anyone else want to bolster my flagging confidence here?

cheers
Mark

[albertaphil]

Hey Mark, don't be scared by the diesel. Frankly, I find them easier to understand than gassers...the fuel and air dont need to mix before they go into the engine.

I don't have any experience with your engine but I have had 4 mkii vw 1.6l diesels apart, and all of them had cracks between the valves and none of them pressurized the cooling system.

My one head gasket failure was on a caterpillar diesel, and the pressure in the cooling system is what tipped me off. I don't know how much your time is worth, but had gaskets don't usually cost too much.

I would get New bolts if I were you. You get one chance to squeeze your gasket and when the last bolt goes "snap" and you have to remove the head again to get at the broken piece it can elicit major profanity!

Moreover, im willing to bet that the head bolts on your engine are "torque-to-yield" type that can only be used once anyway.

[mark_in_manchester]

hey Phil - thanks for your comments. I only work casually at the moment, so my time is not worth much. I'm starting to see the job ahead more clearly - perhaps fit the newly acquired spare engine and see if it works, using the opportunity to remove head on existing one and see if i can get it back on again!

Where does one buy the (presumably high tensile) bolts required? I'll be able to specify thread dia / pitch etc etc...or are these sold as effectively objects with a VW or Daihatsu part number?

cheers
Mark

[Bert in Weesp]

On my 2 gasket jobs on the Daihatsu I used the original bolts. Yes it's high torque but the diameter is quite large, so to be honoust I never thought of replacing the bolts.
It's a little strange feeling when torquing the bolts, the last end to final torque the bolts will start stetching a little so where you normally feel the torque rise as you turn, just before final torque it'll feel like the torque does not rise, that's because the bolts are tensioning/stretching . Normal behaviour. keep on turning till torque is reached.
I do suggest a new timing belt, if the old one is fairly new it is possible to re-use but then do not tension it as a new one ( it'll ruin the teeeth on the belt ) but be sure that on the long end of the belt you can twist it more than 90 degrees, better 120.

[mark_in_manchester]

This is all very helpful and is increasing my confidence (and, by extension, lessening my normal and residual sense of doom!) significantly. Many thanks, especially for the hint on final torque. I would have assumed from 'feel' that I was stripping the thread or about to wring the head off the bolt.

[pietenpol2002]

And in the interest of accurate torquing, don't forget to lubricate those threads.

[albertaphil]

Again I Will emphasize that I have exactly zero experience with diahatsu. But with vw the bolts are specifically one time use and they are vw part numbers although many aftermarket suppliers provide them. They aren't all that expensive.

With the vw, tightening the head bolts is not done by torque. That is, there are a couple of steps of tightening up to a particular torque value that I can't remember and which isn't important here, but the last steps are to sequentially tighten all bolts a number of degrees without measuring torque. If the diahatsu manual does not have a method beyond just tightening to a particular torque value then they likely aren't torque-to-yield bolts, and you should be fine reusing them. But on the vw I really wouldn't recommend it for the price of the bolts vs (another) New head gasket to replace the one you just ruined.

[mark_in_manchester]

Thanks guys. I finally worked up the courage (thanks to your wise counsel) to refer to the destructions - a hard-to-find manual which came, via another miracle of the interweb, from New Zealand ebay. It mostly contains exploded drawings, with the odd outburst of Japlish. Actually that's not fair - what text there is, is quite clear. Fig 5-16 - Cylinder Head Removal and Installation (1) - helpfully asterisks 'parts which do not permit their reuse', such as the head gasket . (Oh; head gaskets come in thick (1.4mm) and thin ( 1.3mm) versions depending on a fairly accurate measurement of piston protrusion at TDC. Well, I possess a dial gauge and magnetic stand...Bert? Did you get in to this?

The head bolts are helpfully not asterisked - so it looks like one does reuse them, tightening bit by bit following the recommended tightening pattern to 8.8-9.5 kgm (units not given - took a lot of digging - didn't sound like very many Nm!).

Before I do this, I found a very small seep on one metal coolant pipe. I have a spare, and I've just cleaned and painted it. It's not going to fix this problem, is it, but hey...

[Bert in Weesp]

(Oh; head gaskets come in thick (1.4mm) and thin ( 1.3mm) versions depending on a fairly accurate measurement of piston protrusion at TDC. Well, I possess a dial gauge and magnetic stand...Bert? Did you get in to this?

I know I used the 1.4 mm gasket, but the is some confusion in my book about identification between the 2. Basicly bokk tells me to put back what was in.


The head bolts are helpfully not asterisked - so it looks like one does reuse them, tightening bit by bit following the recommended tightening pattern to 8.8-9.5 kgm (units not given - took a lot of digging - didn't sound like very many Nm!).

My Dutch book talks about 85-95 nm (8.5-9,5kgm) according mentioned pattern, but in several stages. say start with a lot less and work your way op per 1 or 1,5 kgm is what I did.

[mark_in_manchester]

Thanks again, Bert

[BertTrack]

I don't really have a clue when it comes to that engine Bert.

I imagine they used different thickness to compensate for design changes or, maybe the higher one for the turbo version?

But it could be based on measurement just the same. Really no clue here.