Cold thermostat forcing fluid out the overflow bottle?

[TheOtherLeft]

Hiya gurus,

I have a small problem with my colling system.

I had an Adrad (natrad) radiator installed on my Suzuki back in April this year due to a leak in my factory one. I also got my hoses replaced and the thermostat was deemed to be OK.

Since April I've had to add about 200ml of water as there seems to be a very small leak.

I've checked for dried coolant around the joins and couldn't find any. I've run the engine with the rad cap off and there were no bubbles and the coolant isn't milky. I changed the engine oil/filter a few months ago and it was fine too. There is no milky residue on the inside of the oil cap either.

I've just been back to Natrad and the guy said it was common for cold thermostats to cause coolant to overflow slightly and hence drain out of the overflow bottle.

Whilst this seems to make sense in theory as the thermostat is at the bottom of the system and hence will remain closed even though the coolant is heating up at the top of the block. Hence the increased volume of the hot coolant will go into the overflow bottle and has the potential to drain out slightly before the thermostat opens the system can circulate as per normal.

I've never experienced this issue before so wondering if the natrad guy was just trying to palm me off.

Could this be the case of the thermostat being on its way out?

Is adding 200ml of water every 7 months or so OK or a sign of a leak?

Thanks,
Ben

[chimpboy]

The overflow bottle should be able to cope with any "normal" changes in coolant level - ie expansion due to heat. That's what it's for. Whatever is going on with the thermostat, there is something wrong if it is causing actual coolant loss.

Just my opinion.

[RAY185]

200ml in 7 months is almost negligable but I'd say you have a very slight leak somewhere and you're not going to find it by looking for dried coolant. Get a pressure test done (surprised your Natrad guy didn't suggest it). As Chimpboy said, your overflow bottle can cope with the small amounts of fluid expansion of a properly operating system. Doesn't sound like a thermostat problem to me at all.

Are you noticing the coolant loss in the radiator or in the overflow bottle? If in the bottle, are you filling it to the top or to the full line?

[TheOtherLeft]

200ml in 7 months is almost negligable but I'd say you have a very slight leak somewhere and you're not going to find it by looking for dried coolant. Get a pressure test done (surprised your Natrad guy didn't suggest it). As Chimpboy said, your overflow bottle can cope with the small amounts of fluid expansion of a properly operating system. Doesn't sound like a thermostat problem to me at all.

Are you noticing the coolant loss in the radiator or in the overflow bottle? If in the bottle, are you filling it to the top or to the full line?

I suggested a pressure test but the natrad guy dismissed it.

I only notice the loss in the overflow bottle. When I check the radiator it is full so the rad cap is working as it should. I topped it up to the full line not the top of the bottle.

Maybe I'll find another place to get it tested.

[RAY185]

Yeah definately sounding like a very slight leak, will probably have to stay under pressure for a while to find it. Don't forget to check under the dash around the heater if yours has one/is connected.

[TheOtherLeft]

As I haven't found any bubbling in the coolant or oil in the coolant or water in the oil can I discount a head gasket issue? What other checks can I do at home to check for a cracked head gasket? I don't have a compression tester nor can I do a leak down test.

[Guy]

30Ml a month, 1ml per day ( roughly ) .. I dont like your chances of finding it...
A slightly dicky seal on the radiator cap could so it.
a minor weap from a hose where it joins up could do it
a minor leak in a gasket that warms the intake manifold could do it as the engine heats up or cools down.. You really could chase this forever.
as for trying to pressure test for it ... a leak that slow there will be bigger pressure variations in the block warming up or cooling off that you will be able to detect with even a very good pressure unit.

I know my pajero uses about 50 ml a month ... I honestly could not care less, the system holds about 8 litres from memory .. a loss of 0.something % is not of significant concern in my opinion in a system with so many possibilites of some loss.
I top it up every other month or so, I check it regularly just like I do the oil, ATF, air pressure in the tyres etc .. if it starts to creap up I will chase it further. Or I will pop some stop leak into it.

[RAY185]

I agree it is an almost negligable loss and could probably be ignored until it gets worse but depending on where the leak is, it could well be found with a pressure test.

A system that has a cap pressure of 12psi that is pressure tested at 15+psi will potentially show up an annoying leak like the one suspected quite easily. Like I said, it's likely that it will need to stay pressurised for a while until a drip can be seen.....depending on it's location.

[DamTriton]

Could be a leaking cyl-waterjacket headgasket too. May close itself up due to thermal expansion as the engine gets warm, but in the interim pressurise the coolant enough to blow coolant out of the overflow bottle. This could explain why the overflow bottle may not cope with the "expansion" of coolant fluid volume

[80's_delirious]

I had a radiator that I was sure was leaking slowly, turned out to be a dodgey radiator cap which was letting to much waste into the radiator overflow bottle which on turn overflowed and tricked out onto the lower half of my radiator leaving a nice red stain.
I changed the cap for another one I had laying about and it stopped doing it.

[TheOtherLeft]

Thanks for the tips guys.

It appears to be a weeping o-ring on my coolant pipe which appears to be common in my engine series.

[Clanky]

As I haven't found any bubbling in the coolant or oil in the coolant or water in the oil can I discount a head gasket issue? What other checks can I do at home to check for a cracked head gasket? I don't have a compression tester nor can I do a leak down test.

If the coolant is being burnt in the cylinder and going out the exhaust, check for a spark plug running a different colour. May be clean (steam cleaned by the water) or crusty (from the coolant salts) But if the amount is really small it may not be noticeable.

[RAY185]

Thanks for the tips guys.

It appears to be a weeping o-ring on my coolant pipe which appears to be common in my engine series.

Good stuff.