Underheating?!

[missfixit70]

If the stat fails it does NOT allow coolant to pass through the Rad

You are referring to Bongos I presume, not all cars, and by fail you mean 'fails to open'.

I've read quite enough on BF about Bongo cooling systems on here - more than enough to make my head spin or, to be more precise, to leave me thinking there are a lot of (self elected?) experts, all of whom think they are right and yet who have struggled (wht?) to agree on how the Bongo coolant system works (I recall a diagram showing the coolant system that some people were not happy to agree as being correct - was TGP one of them - it looks like an official diagram but the red and blue bits of the circuit are a BF addition). So I'm outa that debate. I tend not to think I am right, but I do try and use what little understanding I gather, in order to guide me. So far, as in (1) and (2) in my earlier post, the results have suggested, most gratifyingly, that I have been right in the actions I took (or insisted obstinate others took ).

Mike, the thread I have linked to on the cooling system is about the most productive that has been on the forum in determining how the system works & coming up with a correct diagram & understanding of the system, all without arguments & people are listening to what others have to say

[mikeonb4c]

If the stat fails it does NOT allow coolant to pass through the Rad

You are referring to Bongos I presume, not all cars, and by fail you mean 'fails to open'.

I've read quite enough on BF about Bongo cooling systems on here - more than enough to make my head spin or, to be more precise, to leave me thinking there are a lot of (self elected?) experts, all of whom think they are right and yet who have struggled (wht?) to agree on how the Bongo coolant system works (I recall a diagram showing the coolant system that some people were not happy to agree as being correct - was TGP one of them - it looks like an official diagram but the red and blue bits of the circuit are a BF addition). So I'm outa that debate. I tend not to think I am right, but I do try and use what little understanding I gather, in order to guide me. So far, as in (1) and (2) in my earlier post, the results have suggested, most gratifyingly, that I have been right in the actions I took (or insisted obstinate others took ).

Mike, the thread I have linked to on the cooling system is about the most productive that has been on the forum in determining how the system works & coming up with a correct diagram & understanding of the system, all without arguments & people are listening to what others have to say

Its good to know that at last there is concensus on this. Lets hope its the right one. I'll try and take a peek.

Haydn - it's the gauge I'm referring to, not the stat (it'd be hard to observe the latter in situ!). My original answer did say this explicitly but got lost due to not noticing someone else was posting.

[haydn callow]

Not sure where you are coming from there Mike.....If when you changed the gauge it went from zero to 11 o'clock in five mins instead of 10 mins....the cooling system it'self hasn't changed at all and the actual temps are no differant....it's just that the 2 gauges have differant parameters(or one was damaged).......(bending the needle would also give differant readings but down below all is the same). Your Bongo was still taking the same amount of time to reach whatever temp it was reaching....one of your gauges was telling lies.

I do not put myself forward as a expert and am quite open to being shot down...not a problem....in the diagram post I put forward the thought that the stat fails open and was corrected...after studying a stat I now see that this is the case...however there are 2/3 peeps on this forum who are very knowledgeable and they are as we speak putting their heads together for the good of us all...long may they do so...it really is a very informative topic....however I also think we non experts con somtimes put forward valid views....

[mikeonb4c]

Not sure where you are coming from there Mike.....If when you changed the gauge it went from zero to 11 o'clock in five mins instead of 10 mins....the cooling system it'self hasn't changed at all and the actual temps are no differant....it's just that the 2 gauges have differant parameters(or one was damaged).......(bending the needle would also give differant readings but down below all is the same). Your Bongo was still taking the same amount of time to reach whatever temp it was reaching....one of your gauges was telling lies.

I do not put myself forward as a expert and am quite open to being shot down...not a problem....in the diagram post I put forward the thought that the stat fails open and was corrected...after studying a stat I now see that this is the case...however there are 2/3 peeps on this forum who are very knowledgeable and they are as we speak putting their heads together for the good of us all...long may they do so...it really is a very informative topic....however I also think we non experts con somtimes put forward valid views....

Aaaaaaaaaaaaaaaaaaaaarghhhhhhhh. Sorry, should have made it clearer. It didn't change the gauge, I changed the thermostat. The needle on the gauge then only took 5 mins or less to move off the COLD end stop towards 11.00 oclock, whereas before it took 10 mins or more to do it. There was a very clear change in the gauges behaviour (and in the time for car heaters to work)

Kirsty - I've tried reading that thread. Can't manage all 10 pages (pl. forgive me) but this comment from widdowson summed it up for me:

I read through that post (marathon job ) and gleaned quite a lot from it. Take out the 'handbags at dawn' stuff and the numerous diversions, it made very interesting reading.

One thing it did highlight, and this one is showing similar signs, is that no one really is 100% sure how the system works in the finer detail. But I think it is only the finer detail where folk are disagreeing.

Going back to object of the excercise, from my perspective, all I am trying to get out of this is an accurate diagram which I can print out, take to the van, and and check things out.

Prior to that the thread had directed me to the factsheet in the members area, which I read with some concern. Its a useful cut and paste of useful observations (no more) from previous threads, just about all of which I'm familiar with, but I was concerned about some puzzling inclusions. Like this, under 'Possible Causes' [of overheating]:

7. Manifold gasket blown
Usually accompanied by lots of steam and a high-pitched squealing noise. The
number one stud is particularly vulnerable and, if snapped, may need drilling out
and replacing.

I'd expect the factsheet author to know that squealing, broken studs and exhaust manifolds (and their gaskets) was one issue (that has bothing to do with overheating), and head gaskets and lots of steam (in the exhaust tract) was another

Later on, the famous authoritative looking diagram appears though (as its creator has always acknowledged) it is not an authoritative diagram on the Bongo coolant system, but someones best guess. As others have observed (e.g. stilldesparate on the thread you pointed me to) its a moot point whether the outlet from the radiator top hose should be in red or blue (I'd say blue, as its cooled coolant). It'd be nice to see the water pump include in the circuitry too.

My overall problem with all of this is that none of us are Bongo coolant system experts. Even the best of us - Dandy and TGP come to mind as two who lead the field - are struggling to be certain (its noticeable that Dandy is frank about that - to his credit, as it ensures others don't hang on his words when they shouldn't). In the face of that, I think:

* The practical tips are the best stuff
* leave theory out of factsheets as much as poss. and accept that until we get a definitive expalantion from a suitable Mazda engineer (which I'd love to explore the possibility of - anyone got an idea how we might do that?) its best to stress that we are guessing.
* Re-evaluate ideas in the light of evidence/observations that suggest it might be good to do so.

[haydn callow]

its a moot point whether the outlet from the radiator top hose should be in red or blue (I'd say blue, as its cooled coolant).

Do you mean outlet from the rad bottom hose ?
there is only one smallbore outlet from the rad top and this goes to the Expansion tank and is always HOT after warmup. (very quickly.)

[dandywarhol]

Don'forget Mike...the Bongo gauge has a dead area...It remains on 11o'clock from about 55C to 110C ....useless......unless you have a Mason fitted or the Mod I suggest (costs 5p)

Yup, appreciate that. I wonder though if most cars of that vintage aren't the same and thinking about it, it's easy to see why. As far as the manufacturer is concerned, the user only needs to know that their engine has warmed up OK, and that it isn't overheating. The gauge moving around the centre band may only cause them to worry about the natural fluctuations that can occur and that are broadly speaking 'normal' (only us obsessive Bongo type geeks want to watch its every movement, and may know how to interpret them ).

All this brings back a memory of my older cars, where I'm sure I can recall seeing the needle position varying more than it did on the Sunny or does on the Bongo. I wonder if at some point the idea crept in that it would look great to users if their engine temp appeared rock steady even if in fact it wasn't, as crude old thermostat technology was being used. Really, the effort would be better directed to keeping these engines running at the optimum temp but I assume generally that is not done. Does anyone know if more intelligent engine temp maintenance devices are in use these days (other than on racing cars)?

PS - curlew. Maybe Haydns concern is you have an airlock in the system due to incomplete bleeding. If so, caution would seem sensible. can the garage reassure you that is not the case? It seems odd that the opportunity to test and/or change the thermostat was not undertaken during ht erebuild. The even more interesting possiblity arises that the overheating was caused by a thermostat that failed to open. If the temp sensor was downstream of that - or possibly even if upstream but next to it - it may well register cold even if core temp is hot, as there is no flow around the engine. I'd always assumed the small bleed hole in the thermostat was to allow a little water to pass and thus warm it, but this may be insufficient in volume to reliably immerse and warm the temp sender in hot water. All the above is speculation by a non-mechanic (moi!) so may be off the mark

Thats what I think.

A capilliary gauge is miles more accurate but moves a lot - frightens peeps. Dampened gauges work fine if the rest of the system is ok.

The hole with the mini spacehopper in it is a jiggle pin - designed to allow air pass through when refilling/ bleeding the system.

[mikeonb4c]

Thanks Dandy - it comes back to me now (the jiggle pin thing). After I'd written it I noticed you repeating your thought about how the thermostat actually gets warmed up and it sounded right to me and also made a lot of sense out of how the Bongo doesn't appear to warm up just ticking over on the drive but does so quickly after that once you are underway and revs are higher.

[mikeonb4c]

its a moot point whether the outlet from the radiator top hose should be in red or blue (I'd say blue, as its cooled coolant).

Do you mean outlet from the rad bottom hose ?
there is only one smallbore outlet from the rad top and this goes to the Expansion tank and is always HOT after warmup. (very quickly.)

You (should) know what I'm driving at. Cooled coolant (thats in relative terms,, clearly its still hot) exiting the radiator by whichever route it exits it might (its a moot point i.e. one not closed to debate) be usefully shown shown somewhere as a blue stream. Thats how it struck me anyway (and stilldesperate, but maybe I/we need to study the diagram more and reflect).

I'll leave it to the draughtsperson (PC me ) how they do that and to the editorial panel commissioning the work to decide if they should

[rita]

Hi,regarding thermostats failing in the closed position.I can remember a few years back,getting a Fail Safe thermostat fitted.

This stat was designed to Fail Open if the engine overheated.

I dont know if you can still get them.

[haydn callow]

you said....From the radiator top...the only coolant pipe which exits the top of the radiator is a smallbore pipe that goes up to the expansion tank....this exiting coolant is NOT cooled by the rad as it dosn't pass down through it....the temp of this coolant is almost the same as the coolant entering the rad from the engine.
If you ment the rad bottom hose then you are correct..this exits the rad after being cooled on it's passage down through...after the stat opens

[haydn callow]

Hi,regarding thermostats failing in the closed position.I can remember a few years back,getting a Fail Safe thermostat fitted.

This stat was designed to Fail Open if the engine overheated.

I dont know if you can still get them.

I belive I came across those years ago Moggies etc which is why I thought the Bongo one might be the same till I was "correctly" corrected.

[missfixit70]

you said....From the radiator top...the only coolant pipe which exits the top of the radiator is a smallbore pipe that goes up to the expansion tank....this exiting coolant is NOT cooled by the rad as it dosn't pass down through it....the temp of this coolant is almost the same as the coolant entering the rad from the engine.
If you ment the rad bottom hose then you are correct..this exits the rad after being cooled on it's passage down through...

But only if the vehicle is moving (for airflow across the rad) or the fans are running & the engine is warm enough for the stat to open If the vehicle is stationary, with no airflow across the rad (ie when bleeding) this will be warm/hot.

There is no simple - "this should be cool & this should be hot or warm" it depends on what point in the control process it's at (discussed at length in the aforementioned & linked to thread )

[haydn callow]

absolutely........

[rita]

Hi,regarding thermostats failing in the closed position.I can remember a few years back,getting a Fail Safe thermostat fitted.

This stat was designed to Fail Open if the engine overheated.

I dont know if you can still get them.

Found the supplier.MotoRad Fail Safe Thermostats.

[haydn callow]

http://www.motoradusa.com/products/fail ... index.html

Could somone go to this link and watch the VIDIO...they state ...when your vehicle overheats the "normal" thermostat WILL FAIL....Dosn't have to do this ??

And surely even their failsafe could faiy before a high enough temp is reached to trigger the lock