Cracked Block info

[MR2Mania]

Dino,do you think there would be any reason not to fit a higher pressure rad cap?

No, I can't think of a reason NOT to fit one, other than I think it would be a bad idea to fit one to cure an overheating problem with the stock setup (you'd be masking the problem, then).

But at the same time, I can't see how it helps other than to raise the temperature at which the coolant boils. Having said that, I fitted one on my only a couple of weeks ago! But the reason I did so was to see if it cured the "coolant bubbling on shut down" characteristic that we get with out tubbies. Too early to tell whether it's had an effect (I've barely driven it in the last couple of weeks).

[Bry]

Dino,do you think there would be any reason not to fit a higher pressure rad cap?

No, I can't think of a reason NOT to fit one, other than I think it would be a bad idea to fit one to cure an overheating problem with the stock setup (you'd be masking the problem, then).

But at the same time, I can't see how it helps other than to raise the temperature at which the coolant boils.

One of the reasons the Aussie guy thinks that they crack is due to a build up of steam pressure in between the cylinders,so his solution (part of it anyway)was to raise the temperature at which the coolant boils by way of fitting a higher pressure cap thus reducing the amount of steam pressure and hopefully reducing the risk of the block cracking,does this sound right?

[MR2Mania]

One of the reasons the Aussie guy thinks that they crack is due to a build up of steam pressure in between the cylinders,so his solution (part of it anyway)was to raise the temperature at which the coolant boils by way of fitting a higher pressure cap thus reducing the amount of steam pressure and hopefully reducing the risk of the block cracking,does this sound right?

Yeah, that kinda makes sense, but it concerns me that there's steam in the system to start with. Really, you should only get this if there's already air in the system (ie bad bleeding), but if the system is fully bled with coolant end-to-end, how can steam be released anywhere, other than through the cap? That's the only thing I don't understand in this guy's theory.

[Bry]

One of the reasons the Aussie guy thinks that they crack is due to a build up of steam pressure in between the cylinders,so his solution (part of it anyway)was to raise the temperature at which the coolant boils by way of fitting a higher pressure cap thus reducing the amount of steam pressure and hopefully reducing the risk of the block cracking,does this sound right?

Yeah, that kinda makes sense, but it concerns me that there's steam in the system to start with. Really, you should only get this if there's already air in the system (ie bad bleeding), but if the system is fully bled with coolant end-to-end, how can steam be released anywhere, other than through the cap? That's the only thing I don't understand in this guy's theory.

As I understood it,the thin walled part of the block gets alot hotter than other parts of block and the coolant that flows between the thin walled parts gets boiled up creating the steam/pressue build up,or have I interpreted it wrong

[MR2Mania]

As I understood it,the thin walled part of the block gets alot hotter than other parts of block and the coolant that flows between the thin walled parts gets boiled up creating the steam/pressue build up,or have I interpreted it wrong

I think you're intepretting it as the guy suggests, but I'm not sure it's right.

That part of the block won't get any hotter because it's thinner. What it *will* do though promote more heat transfer through that part because it's thinner, and hence the coolant behind that part of the wall will in theory get hotter. However, how can it produce steam there if it's a sealed system with no air in it? That's the whole point of a pressurised system. The hotter it gets, the more pressure it'll create. But when the pressure gets too high, it'll be released at the cap. So unless he's talking about that part of the block cracking from excessive heat, I can't personally see anything in his argument. If this is the case, then even a higher rated cap won't help, because it too will allow the coolant to get as hot (although the higher pressure cap will mean that the coolant should not reach boiling point at this temp).

[Bry]

As I understood it,the thin walled part of the block gets alot hotter than other parts of block and the coolant that flows between the thin walled parts gets boiled up creating the steam/pressue build up,or have I interpreted it wrong

I think you're intepretting it as the guy suggests, but I'm not sure it's right.

That part of the block won't get any hotter because it's thinner. What it *will* do though promote more heat transfer through that part because it's thinner, and hence the coolant behind that part of the wall will in theory get hotter. However, how can it produce steam there if it's a sealed system with no air in it? That's the whole point of a pressurised system. The hotter it gets, the more pressure it'll create. But when the pressure gets too high, it'll be released at the cap. So unless he's talking about that part of the block cracking from excessive heat, I can't personally see anything in his argument. If this is the case, then even a higher rated cap won't help, because it too will allow the coolant to get as hot (although the higher pressure cap will mean that the coolant should not reach boiling point at this temp).

I see what you're saying now(I knew one day I'd regret bunking off my physics lessons at school )At least we know that this Block cracking definately isn't a myth and if there's even the remotist chance that a higher pressure rad cap might help,it's gotta be worth the £20 (just bought a TRD one for a tenner ) and if it don't do diddly then it's still a bit of Bling

[MR2Mania]

I see what you're saying now(I knew one day I'd regret bunking off my physics lessons at school )At least we know that this Block cracking definately isn't a myth and if there's even the remotist chance that a higher pressure rad cap might help,it's gotta be worth the £20 (just bought a TRD one for a tenner ) and if it don't do diddly then it's still a bit of Bling

LOL! Exactly! Bling with a function (*possibly*!).

I still think for any decent builds, the block should be ultrasonically tested. Wished I'd done mine, now! I just took Fraser's word that he'd sourced me a brand new thick walled block, which I then went and overbored! DOH!!

[Bry]

I see what you're saying now(I knew one day I'd regret bunking off my physics lessons at school )At least we know that this Block cracking definately isn't a myth and if there's even the remotist chance that a higher pressure rad cap might help,it's gotta be worth the £20 (just bought a TRD one for a tenner ) and if it don't do diddly then it's still a bit of Bling

LOL! Exactly! Bling with a function (*possibly*!).

I still think for any decent builds, the block should be ultrasonically tested. Wished I'd done mine, now! I just took Fraser's word that he'd sourced me a brand new thick walled block, which I then went and overbored! DOH!!

Fingers crossed for you mate [-o<

[Guest]

I'm with Dino on this one about the pressure side of things and I see exactly what he means. When your car is running with a standard pressure rad cap and the rad cap isn't venting anything the normal running pressure in your system must be below the venting pressure of the stock rad cap....in which case fitting one that vents at an even higher pressure isn't going to change the working pressure of the coolant system.

Perhaps the difference is just replacing what may already be a worn/tired rad cap? Perhaps simply fitting a new stock rad cap is enough because the original may be worn and venting at too low a pressure....although again as Dino says - you'd have a coolant problem.

Sometimes it's possible for a hotspot to cause tiny bubbles of gas to be formed which collapse in on themselves almost immediately (it's what makes the loud roaring/hissing sound in a kettle before it boils properly) and that forming/collapse can sometimes cause pitting of the metal and can also act to insulate the metal against the coolant - thereby creating minute hotspots that suddenly chill when the bubble collapses. I've been lead to believe this can be a problem in rotary engines where there are hot and cold parts to the engine, perhaps on the Tubbys thess parts of the block are natural hot spots because of the design of the engine and cooling galleries and a similar thing happens?

Just idle thoughts on a horrible Friday afternoon.

Cheers,
Si.

[steve b]

N. Having said that, I fitted one on my only a couple of weeks ago! But the reason I did so was to see if it cured the "coolant bubbling on shut down" characteristic that we get with out tubbies. Too early to tell whether it's had an effect (I've barely driven it in the last couple of weeks).

Mine did this when i got it and if you think about it is really isn't good. If it boils on shutdown then its overheated, if you've got the correct coolant in and a 1.3kg cap then it would have to reach about 140degrees or so to boil.

I found a mild weep from the rad bleed valve, so sorted that, i then
everytime i drove it for probably 8 - 9 times let it cool and topped it up again, only about 3 inches of the top pipe by the filler was empty each time. Now the level is always totally full and it doesn't boil on shutdown, i have always had a 1.3kg cap. Other thing to check is the expansion tank is full as else on cooldown it'll suck air in causing it to boil again.

[MR2Mania]

Mine did this when i got it and if you think about it is really isn't good. If it boils on shutdown then its overheated, if you've got the correct coolant in and a 1.3kg cap then it would have to reach about 140degrees or so to boil.

Good point! Now that I have the MoTeC, I can see the readings on all sensors. Regardless of how long I let the car cool down before switching off, I can still see the temps reach just over 100C when switch off, purely because the pump is no longer circulating the coolant and the hot parts (ir turbo and block) will heat the coolant more. In this respect, maybe the 1.3bar cap would help (make mental note - look out for this next time you take the beast out).

I found a mild weep from the rad bleed valve, so sorted that, i then
everytime i drove it for probably 8 - 9 times let it cool and topped it up again, only about 3 inches of the top pipe by the filler was empty each time. Now the level is always totally full and it doesn't boil on shutdown, i have always had a 1.3kg cap. Other thing to check is the expansion tank is full as else on cooldown it'll suck air in causing it to boil again.

Some more good points, that remind me of some facts people should consider...

1) Silicone hosing: This tends to "breathe", unlike regular rubber hosing, and hence when you use silicon hosing in the coolant system, ideally you should check the coolant level a bit more often, as a bit will bleed through the hoses over time.

2) Bleeding the coolant system: When carrying out the coolant system bleeding, ensure that you've got the right level in the expansion bottle, as no matter how well you bleed it, when the cap opens up (like it can when the engine is switched off!), you *could* suck some air back into the system.

Like you, it took me some time to totally get the air out of the system so that the level didn't drop by half a cup, partly due to both reasons above.

[Guest]

...if anyone's interested for their own cars...while my Rex is getting rebuilt it's getting an electric water pump fitted to replace the engine powered jobbie. This can be kept running after the engine has been shut down to help equalise the temperatures aroundabout - it's even possible to keep the rad fans running to cool things down at the same time.

I know it's suitable for the Rex - not sure if it flows enough volume for a '2 though and I don't know if it would fit easily enough - it's not massively expensive and it's only some electrickey and a beefy water pump/motor.... I can get some details if anyone's interested.

Cheers,
Si.

[MR2Mania]

...if anyone's interested for their own cars...while my Rex is getting rebuilt it's getting an electric water pump fitted to replace the engine powered jobbie. This can be kept running after the engine has been shut down to help equalise the temperatures aroundabout - it's even possible to keep the rad fans running to cool things down at the same time.

I know it's suitable for the Rex - not sure if it flows enough volume for a '2 though and I don't know if it would fit easily enough - it's not massively expensive and it's only some electrickey and a beefy water pump/motor.... I can get some details if anyone's interested.

Cheers,
Si.

Si, I've got to admit, I *have* thought about this for my car, and I even know the pump that I'd use (the Davies Craig pump), but the problem is, you'd somehow have to disable the stock pump, as described before.

I've seen an MR2 engine that someone attempted to "boost" the coolant system on by fitting an inline pump, but to be honest, it seemed to be causing more of a restriction whilst the engine was running than it seemed to help.

I don't have my old engine bits handy to see if I can disable the stock pump easily, and it would probably need the engine out to do it properly (cambelt access isn't at all easy with the engine in the car, let alone trying to do something like this).

Would be interested to hear from Grandpa JJ on this, as he's done a fair bit of engine work and seems to know it well. However, he must be out cruising in his new Hondaaah and hasn't picked up on this thread!

[Guest]

Dino,
That's one of the big reasons why I'm getting it fitted now...I'm pretty much just paying for the parts alone because the engine is out and in bits anyway.

I think it's easier all round in the Rex because there's no cam belt to worry about tensioning so it's just a matter of changing the plumbing and putting a smaller drive belt on that misses out the water pump, air pump and IIRC an idler pulley...although there's probably a bit more to it than that.

My only concern is I'm going to worry at least initially that the pump is running - when it was driven off the engine I knew it was running - now it's electrical though I'll be wondering......can't wait to pick up the car.

All the while I'm looking at this with half an eye on what options come up for modding a Mk1 SC....there are lots of ideas around and I'm hoping to buy one in a little while....watch this space (c:

Cheers,
Si.

[ENSMR2]

I vote to make this thread a sticky. So much vital info to those who are worried about the cracking problem. And to any one considering modifying.

Personally I am going for the thick wall block for my build as well as a 1.3 rad cap. Just to be sure.

Quick question. Wouldn't our turbo timers aid in the cooling? That's why we have them keep our engines running right? I've had mine done so the rad fans come on as well when I turn the ignition off.

I'm also guessing those with a thick wall block won't need to worry about shimming the oil pump and having an electronic water pump.?!?

p.s Dino, did you get my pm's? This pdpMobile thing I use can be pretty naff.


HTH guys,

N

[Bry]

Anyone now thinking of rushing out and buying a TRD 1.3bar cap now,beware of the guy selling fake ones on ebay.They are listed as JDM style and are not original TRD ones from what I can see!

[Dale_V]

Anyone now thinking of rushing out and buying a TRD 1.3bar cap now,beware of the guy selling fake ones on ebay.They are listed as JDM style and are not original TRD ones from what I can see!

If you want the proper stuff, look here http://www.trdsales.com/shop/product.asp?catcode=216 . I've ordered before, great service, cheap prices and obviously top quality!

[Guest]

I'd have thought a turbo timer keeping the engine running will help things loads. To bo honest when I had my Rev 1 Tubby I used to drive the last 10 mins or so off boost to let it cool.

A lekky water pump helps out when driving too because it always runs at the same speed. The only other main benefit for me (parking the car on the street) is I can officially leave the car with the pump and rad fans running and walk away - can't do that when the engine is running because IIRC a cat with a running engine in a public place has to be attended at all times.

I have been wondering how many horses the engine driven water pump uses - perhaps with running at fixed revs the lekky pump may be more efficient than if it were driven by the engine - so perhaps it frees a few more horses....?

Cheers,
Si.

[MR2Mania]

I'd have thought a turbo timer keeping the engine running will help things loads. To bo honest when I had my Rev 1 Tubby I used to drive the last 10 mins or so off boost to let it cool.

Si, I don't agree about the turbo timer thing. Sure, it'll cool down a bit, but as long as the engine is running, the engine is heating the coolant. MR2 engines push out some fair heat. Regardless of how much cool down I gave, on a hot day, I still used to get the gurgle.

Think of it this way, how long does it take for the coolant to get to proper operating temp from cold? In contrast, my Golf diesel could be idleing for AGES from cold and the temp needle will barely budge. I have to put it under some load before it'll start heating the coolant system up.

A lekky water pump helps out when driving too because it always runs at the same speed. The only other main benefit for me (parking the car on the street) is I can officially leave the car with the pump and rad fans running and walk away - can't do that when the engine is running because IIRC a cat with a running engine in a public place has to be attended at all times.

Today, at an Evo dyno day, I noticed that the RC developments demo car was running the same electric water pump I mentioned earlier. Now, THAT car is a monster, however it does run purely on methanol, which means that the engine runs SO much cooler than when on petrol. So much so, that they struggle with getting high enough EGTs to drive the turbo properly!

I have been wondering how many horses the engine driven water pump uses - perhaps with running at fixed revs the lekky pump may be more efficient than if it were driven by the engine - so perhaps it frees a few more horses....?

Or how much the oil pump and alternator consume to run! Someone once told me that had he could see a difference in power on the dyno from merely putting on the car's heater. Obviously, this means that it's putting more load on the alternator. If you were so concerned of such losses though, you'd get the biggest gain from a dry sump setup, IMHO.

[MR2Mania]

Quick question. Wouldn't our turbo timers aid in the cooling? That's why we have them keep our engines running right? I've had mine done so the rad fans come on as well when I turn the ignition off.

The rad fans coming on after ignition is good, but this is only cooling the coolant in the rad. As the coolant is not being circulated anymore, this doesn't really have much of an effect (the temp sensor is right on the engine, so basically this tells us that the coolant around the engine/turbo is getting hot after shut down). This is where an electronic pump that works after shut down would help out.

I'm also guessing those with a thick wall block won't need to worry about shimming the oil pump and having an electronic water pump.?!?

Regardless of whether you get a "thick walled" block, what we should all learn from this is that the only sure fire way of knowing it IS thick walled is to have it ultrasonically tested. It shouldn't cost more than about £60 (it'll save a LOT more money than that if you end up finding it's thin!).

The shimming of the oil pump has NOTHING to do with this issue - it was a Freudian slip by Fonzy, so I hope it didn't throw you off the scent.

p.s Dino, did you get my pm's? This pdpMobile thing I use can be pretty naff.

Sorry mate, my bad. I DID get both your last PMs, but the first one got lost because I haven't quite got used to the PM interface (managed to delete ALL my PM messages when I only selected one to be deleted! ADMINS take note!). And with regards to the 2nd PM, I've just been too busy the last few days to sit down and give one of my usual, detailed (or boring - whichever way you look at it! ) replies.

I'll get round to it though, mate!