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Coolant leak


blackrose
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My Isuzu 55 seems to have a minor coolant leak and when you open the coolant filler cap there's pressure inside even when it's stone cold.

 

I thought it must be the thin hose from the engine header tank overflow under the filler cap to the external header tank as there was a kink in it, but I've replaced that hose this morning with some proper car heater hose and filled up the coolant, but nothing is getting through to the external header tank when I run the engine and it gets hot. 

 

I checked the overflow spigot for blockages before I installed the new hose and blew through the hose into the external header tank and all was ok. 

 

Also there seems to be a small amount of steam coming out from around the thermostat housing.

 

IMG_20221127_133039.jpg

 

IMG_20221127_133118.jpg

 

IMG_20221127_133057.jpg

Edited by blackrose
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It hasn't overheated recently, just a poor paint job by HMI. It's not just the head either. It used to get up to about 95C sometimes but that was before I installed a second skin tank about 10 years ago. Now it stays just over 80C.

Edited by blackrose
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8 minutes ago, jonathanA said:

I'm not sure I understand your problem?  Presumably the level under the engine cap is full and then you add coolant to the other tank. If you loosen the engine cap does coolant leak out. That would prove your new bit of pipe. 

 

I top up the coolant using the engine header tank cap. The external header tank is just an expansion overflow. The problem is that I've got a coolant leak over the engine room floor. The pressure cap doesn't seem to be working and allowing coolant to expand into the external tank. Perhaps it's just a faulty pressure cap? The spring seems ok.

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I think I'd be changing the thermostat gasket.

Also, what are the pressure cap arrangements? The usual pressure cap doesn't seal very well at the top of the filler neck, unless it has a rubber gasket there. Not a problem usually, but when an expansion tank is added, coolant can leak from the engine filler. In a similar set up, I used a pressure cap on the expansion tank, and a flat cap on the engine.

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1 hour ago, Iain_S said:

I think I'd be changing the thermostat gasket.

Also, what are the pressure cap arrangements? The usual pressure cap doesn't seal very well at the top of the filler neck, unless it has a rubber gasket there. Not a problem usually, but when an expansion tank is added, coolant can leak from the engine filler. In a similar set up, I used a pressure cap on the expansion tank, and a flat cap on the engine.

 

Thanks. I've got a feeling the thermostat gasket has blown because of the pressure build up in the system due to the filler cap not releasing the pressure.

 

I've never had a problem with the filler cap not sealing against the neck.

 

56 minutes ago, bizzard said:

And while the thermostat housing is off test the thermostat by suspending it on a bit of thin wire and dunk it into a pan of just slightly off the boil water and it should open.

 

Yes I'll dismantle the thermostat assembly, fit a new gasket and test the thermostat. I might get a new filler cap too.

 

But I need to understand what's preventing coolant from expanding into the external tank and causing the pressure to stay in the system even when the engine is cold, otherwise the new gasket will blow straight away. A new gasket isn't going to solve the problem.

 

Where's the best place to get the gasket?

Edited by blackrose
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16 minutes ago, blackrose said:

 

Thanks. I've got a feeling the thermostat gasket has blown because of the pressure build up in the system due to the filler cap not releasing the pressure.

 

I've never had a problem with the filler cap not sealing against the neck.

,

Yes I'll dismantle the thermostat assembly, fit a new gasket and test the thermostat. I might get a new filler cap too. 

 

Where's the best place to get the gasket?

When the top housing is off it's best to check if it's mating surface is nice and flat, these often bow slightly between the bolt holes. Place a sheet of fine emery or pruduction paper on a mirror or pane of glass and rub it on it and keep checking until its uniformly bright all over, if there is a spigot ''circular rib'' you cannot do this.    Making a gasket is dead easy. gasket paper available from any engineers supplies or online Ebay. Not too thin about a 1 mm thick. Place on the housings bottom mount on the engine and with the ball of a ball pien hammer rub it into the gasket over both bolt holes until it breaks through and leaves two nice holes in the gasket. Pick out the two little discs of the gasket. Now screw the two bolts back in to hold the gasket still whilst you can either tap around the perimeter and central hole with the ball of the hammer until it breaks through or probably better for you is to rub firmly all around and around the central hole with your fingers whiich will leave an impression on the gasket. Remove it and cut out with sharp scissors fo;;owing the impressions.  Use a smear of blue Hylomar sealant when reasenbling.

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1 hour ago, blackrose said:

Thanks. I've got a feeling the thermostat gasket has blown because of the pressure build up in the system due to the filler cap not releasing the pressure.

 

I've never had a problem with the filler cap not sealing against the neck.

Err I think you've found your problem....

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24 minutes ago, jonathanA said:

Err I think you've found your problem....

 

No I don't think so. I haven't found anything, it's just conjecture.

 

Edit: If you're talking about my filler cap comment, it's always sealed against the filler neck and then released when the engine is hot and the pressure has built up. I just meant I've never had coolant escaping from the cap itself, just from the overflow.

 

I'm thinking that for some reason the cap isn't opening now but I don't know for sure..

Edited by blackrose
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1 hour ago, bizzard said:

When the top housing is off it's best to check if it's mating surface is nice and flat, these often bow slightly between the bolt holes. Place a sheet of fine emery or pruduction paper on a mirror or pane of glass and rub it on it and keep checking until its uniformly bright all over, if there is a spigot ''circular rib'' you cannot do this.    Making a gasket is dead easy. gasket paper available from any engineers supplies or online Ebay. Not too thin about a 1 mm thick. Place on the housings bottom mount on the engine and with the ball of a ball pien hammer rub it into the gasket over both bolt holes until it breaks through and leaves two nice holes in the gasket. Pick out the two little discs of the gasket. Now screw the two bolts back in to hold the gasket still whilst you can either tap around the perimeter and central hole with the ball of the hammer until it breaks through or probably better for you is to rub firmly all around and around the central hole with your fingers whiich will leave an impression on the gasket. Remove it and cut out with sharp scissors fo;;owing the impressions.  Use a smear of blue Hylomar sealant when reasenbling.

 

Ok thanks. I have some 1mm gasket material. I didn't realise the thermostat gasket was paper. Blue Hylomar? I think I have some somewhere...

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It looks to me that the thermostat housing is a bit corroded at the joint with the outlet rubber pipe. I have had small leaks on this hose before on my Isuzu 55. Cleaning the housing and/or a new hose should cure it if that is the problem. Mine also holds pressure until the next day and when you open the cap on the mannicooler slowly it bubbles through the header tank. There have been reports of head gasket failure on these engines which would result in a build up of pressure mainly due to overheating.

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49 minutes ago, Mike Adams said:

It looks to me that the thermostat housing is a bit corroded at the joint with the outlet rubber pipe. I have had small leaks on this hose before on my Isuzu 55. Cleaning the housing and/or a new hose should cure it if that is the problem. Mine also holds pressure until the next day and when you open the cap on the mannicooler slowly it bubbles through the header tank. There have been reports of head gasket failure on these engines which would result in a build up of pressure mainly due to overheating.

 

Ok, but my engine has never behaved like this before. Coolant usually flows into the external header tank as soon as it gets hot and expands and I've never observed any residual pressure in the cooling system if the engine hasn't been run for weeks on end.

Edited by blackrose
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When the engine is cold what is the coolant level in the mannicooler? Mine is always full to the brim when I check it  which I tend to do every morning. If it not full it probably wont push fluid into the expansion tank. You may have two distinct problems' firstly the small leak. The castings of the mannicooler and thermostat housing may well have been made for HMI the marinisers and not great at not corroding. There are signs of anitfreeze leaking from the thermostat housing on your pictures. This problem should be easily solved by removing the housing and cleaning it up with a new gasket and/or hose and previously discussed. Secondly the pressure build up. My system has quite a lot of hose in it and this expands under pressure it will hold pressure until you release it like deflating an inner tube. I suggest you sort out the first problem and maybe get a new radiator cap and fill the system up and run the engine. This will ensure the cap is letting by at the right pressure in both directions. Hose leaks don't often show up until the system is under pressure so this maybe the cause of the steam.

Hope this helps!

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Thanks. The engine coolant tank is usually less than half full but it used to expand and come out into the external header tank. It stopped doing this recently. Today I filled it up to about 80% full and it still wasn't coming out.

 

I'll take the thermostat housing off this week and see if I can sort it out. 

 

Are radiator pressure caps universal in terms of dimensions? I think mine is rated at about 1 bar.

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11 hours ago, blackrose said:

Are radiator pressure caps universal in terms of dimensions? I think mine is rated at about 1 bar.

I think the correct one is still available from the successor suppliers at https://www.enginesplus.co.uk/product/water-filler-cap/

The water wont come out until it reaches the top of the mannicooler so warm it up and see if reaches the top when hot. undo the cap very slowly and use a cloth/gloves to prevent any hot water getting on your hands.

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Sorry I can’t tell from your picture. Is the coolant level in your expansion tank below the level of the radiator cap so that the coolant is sucked back into the mannicooler when it cools? Or is the coolant level above the radiator cap so that gravity helps? 

Is the expansion tank cap a pressure cap or is the tank open to atmospheric pressure?

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4 hours ago, Mike Adams said:

I just had another thought -does your expansion bottle include an internal pipe going to the bottom of the container. If that is missing or broken then the engine cannot draw water back from the expansion bottle as it cools down.

 

I'm not sure, I don't think so. But it's always drawn the coolant back out before.

4 hours ago, Mike Adams said:

The water wont come out until it reaches the top of the mannicooler so warm it up and see if reaches the top when hot. undo the cap very slowly and use a cloth/gloves to prevent any hot water getting on your hands.

 

Likewise the coolant has always expanded and come out even when it's only 1/4 full (cold).

 

Thanks for the link to the replacement pressure cap.

2 hours ago, Peugeot 106 said:

Sorry I can’t tell from your picture. Is the coolant level in your expansion tank below the level of the radiator cap so that the coolant is sucked back into the mannicooler when it cools? Or is the coolant level above the radiator cap so that gravity helps? 

Is the expansion tank cap a pressure cap or is the tank open to atmospheric pressure?

 

There is no coolant in the external expansion tank when the engine is cold.

 

The expansion tank isn't pressurised, it's open.

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41 minutes ago, blackrose said:

 

I'm not sure, I don't think so. But it's always drawn the coolant back out before.

 

Likewise the coolant has always expanded and come out even when it's only 1/4 full (cold).

 

Thanks for the link to the replacement pressure cap.

 

There is no coolant in the external expansion tank when the engine is cold.

 

The expansion tank isn't pressurised, it's open.

So am I right in saying that the expansion tank is above the engine so that no vacuum is needed to suck the coolant back when it cools. With yours I assume it just drains back. Does anyone know the pros and cons of this way of doing it rather than the bottle being below the mannicooler and coolant being sucked back in when the engine cools?

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3 hours ago, Mike Adams said:

My mistake I assumed your coolant bottle pipe enters at the top like mine whereas yours goes in at the bottom. Mine is sat on the floor next to engine.

Mine too a milk bottle on the floor but I just wondered if there was any advantage to having it above the engine with the feed in the bottom. If the radiator cap leaks with the bottle above it the coolant could leak out  of the cap but if the bottle is below and the cap leaks you will lose the vacuum. So I suppose it depends which is more likely. An air leak under vacuum or a coolant leak under a small static pressure. Anybody any ideas? Am I correct with this assumption?

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I’m a bit late to this thread but going back to the first picture  surely there shouldn’t be a pressure cap on the engine. The pressure cap should be on the expansion tank, that way the coolant expands with heat and flows up to the tank, when the engine cools down the fluid can flow back into the engine. If you have a pressure cap between the engine and the expansion tank once the engine is switched off the pressure cap will close before all the fluid has flowed back into the engine ……at least, that’s the way it works on my car. 

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My understanding is that it makes no difference as either allow air to escape during expansion and only liquid to return to the system. However you need the correct type of pressure cap that allows the  vacuum created while cooling to draw from the recovery tank and not the atmosphere so it needs to be sealed above the side vent pipe leading to the recovery tank.

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