Mechanics have run out of ideas on how to fix cooling system

[Northern Bongolow]

scanner you could bang a cork in the rad, it wouldnt matter, it is only a bung, it doesnt open/vent. it cannot, as the top rubber seal is always in touch with the rad top ring, the sprung valve does nothing at all.
but it will vent if the rad has the little vent pipe.

[scanner]

scanner you could bang a cork in the rad, it wouldnt matter, it is only a bung, it doesnt open/vent. it cannot, as the top rubber seal is always in touch with the rad top ring, the sprung valve does nothing at all.
but it will vent if the rad has the little vent pipe.

Maybe, if everything hidden away down there is in good order and doesn't leak.
For peace of mind I'd rather have the weakest link where is most easily dealt with.

[The Great Pretender]

scanner you could bang a cork in the rad, it wouldnt matter, it is only a bung, it doesnt open/vent. it cannot, as the top rubber seal is always in touch with the rad top ring, the sprung valve does nothing at all.
but it will vent if the rad has the little vent pipe.

Maybe, if everything hidden away down there is in good order and doesn't leak.
For peace of mind I'd rather have the weakest link where is most easily dealt with.

NB is correct, it’s a shame after all the work members put in to understanding the cooling system you seem to disregard it.

[scanner]

scanner you could bang a cork in the rad, it wouldnt matter, it is only a bung, it doesnt open/vent. it cannot, as the top rubber seal is always in touch with the rad top ring, the sprung valve does nothing at all.
but it will vent if the rad has the little vent pipe.

Maybe, if everything hidden away down there is in good order and doesn't leak.
For peace of mind I'd rather have the weakest link where is most easily dealt with.

NB is correct, it’s a shame after all the work members put in to understanding the cooling system you seem to disregard it.

In that case why is there?

1 A pressure cap there at all, when all that is needed is a blank cap to seal off the radiator, other cars manage to cope quite well with one.

2 If there has to be a pressure cap why should it have a lower rating that the one on the header tank?

I simply stated that I thought I had read somewhere that it was better to have the lower rated cap where it should operate most usefully, not where it appears to serve no useful function.

If that is such a misconception perhaps a clever person like yourself, who understands the system so much better than me, could kindly explain the logic behind why the radiator (where there is apparently no need for venting) should have a lower rated cap than the header tank (where venting, if any, surely should happen), or indeed why it should have a pressure cap at all.?

[alvino]

Is anyone able to give a brief description of whats involved in replacing the Lower Temperature Sender Unit and if necessary the fan relay switch. How long should this typically take a competent mechanic (not me!). The reason I ask is that we have been advised that there is a minor issue with the head gasket. The mechanic says we can ignore the head gasket issue (rough starting for a couple of seconds before all 4 cylinders start to hum nicely), however, if replacing the Lower Temperature Sender Unit and fan relay switch require some of the same parts moving out of the way as for the head gasket, then maybe we will bite the bullet and get it all done together.
Thanks for all the help so far guys. My wife and I knew next to nothing about mechanics until we bought an 18 year old Bongo. Its all a good learning experience and we do love the bongo so would like to get it running nicely if poss.

[widdowson2008]

NB is correct, it’s a shame after all the work members put in to understanding the cooling system you seem to disregard it.[/quote]

In that case why is there?

1 A pressure cap there at all, when all that is needed is a blank cap to seal off the radiator, other cars manage to cope quite well with one.

2 If there has to be a pressure cap why should it have a lower rating that the one on the header tank?

I simply stated that I thought I had read somewhere that it was better to have the lower rated cap where it should operate most usefully, not where it appears to serve no useful function.

If that is such a misconception perhaps a clever person like yourself, who understands the system so much better than me, could kindly explain the logic behind why the radiator (where there is apparently no need for venting) should have a lower rated cap than the header tank (where venting, if any, surely should happen), or indeed why it should have a pressure cap at all.?[/quote]


Hi scanner
In answer to your point above, you're right, it doesn't need a PRESSURE cap - just something to block the filling hole. Pressure control is governed at the expansion tank.
The ONLY reason the radiator has a cap at all is so that it can be filled with coolant.

[scanner]

Hi scanner
In answer to your point above, you're right, it doesn't need a PRESSURE cap - just something to block the filling hole. Pressure control is governed at the expansion tank.
The ONLY reason the radiator has a cap at all is so that it can be filled with coolant.

Thank you for that - the very point I was attempting to make.

I cannot see any reason for the fitting of a redundant component and certainly no good reason to fit a redundant component with a lower rating than the one supposed to do the job.

Perhaps an expert can explain the logic behind it - if 0.9 is good enough for the rad 0.9 must be good enough for the header tank or vice versa.

[rita]

Both caps should be rated at 1.1..

[scanner]

Both caps should be rated at 1.1..

Not according to our experts.

[Muzorewa]

But it doesn't matter what the one on the rad is rated at if there's no vent in the neck of the filler, there's nowhere for the coolant to escape to even if it's past the spring

[scanner]

But it doesn't matter what the one on the rad is rated at if there's no vent in the neck of the filler, there's nowhere for the coolant to escape to even if it's past the spring

So why is it a pressure cap at all and if it has to be a pressure cap one with a lower rating than the header tank?

[widdowson2008]

But it doesn't matter what the one on the rad is rated at if there's no vent in the neck of the filler, there's nowhere for the coolant to escape to even if it's past the spring

So why is it a pressure cap at all and if it has to be a pressure cap one with a lower rating than the header tank?

Probably because you can't BUY a cap that ISN'T a pressure cap.
It's cheaper for the manufacturers to use one that is readily available than to produce a special. Trust me - it is purely to cap off the radiator and has absolutely no other function.

[scanner]

Probably because you can't BUY a cap that ISN'T a pressure cap.

Yes you can.................................
They manage to get them in NZ.................
http://www.partzonline.co.nz/tridon-rad ... 48852.html

(First one I found - they must be available over here.)

Trust me - it is purely to cap off the radiator and has absolutely no other function.

I'm not arguing, just puzzled why some folk seem to think it must be a 0.9 one?

[rita]

You can buy Non pressurised radiator caps ,could some one give me the Mazda part number for the Radiator Cap and the Expansion Tank cap.

Thanks.

[widdowson2008]

Trust me - it is purely to cap off the radiator and has absolutely no other function.

I'm not arguing, just puzzled why some folk seem to think it must be a 0.9 one?[/quote]

No idea - absolutely NONE.