Cold Bottom Hose

[haydn callow]

What happens is !!!! The standard Bongo temp gauge is activated by a sensor which is located in the cylinder head......When the coolant in the cylinder head reaches 25C the gauge starts to move....when the coolant in the cylinder reaches 45C the gauge will be at it's "normal" 11 o'clock position.......it will then sit at that position untill the coolant in the cylinder head reaches "approx" 110C.....and you are on the cusp of a overheating event.....

Whatever you used to get those figures needs checking. As you know I had a thermistor in direct contact with the coolant located in the top hose, the temp was in the high 60's before any movement then quickly reached 11 o clock.

O.K. Did a very careful recheck to-day.....My standard Bongo gauge moves off the COLD stop at 28/29C..........It reaches the "normal" 11 o'clock position at 40C........my sensor is positioned within the Top hose about 8inches from the Cylinder Head outlet.......this has been much the same on all 3 bongos.....the one at the moment is a 2.5 V6 but I would think the gauge sensors are all the same values.........I have used the i-alert to measure coolant temp and I have used 2 differant sensors ....both gave the same readings....The i-alerts seem to all give the same readings +/- 1C and when tested in a pan of water with a digital (infer red) temp gauge they are extreamly accurate.

[mikeonb4c]

out of interest, has anyone additionally put temp. sensors directly either side of the thermostat to see what local temperatures are there for corresponding top hose temps?

[haydn callow]

Yep....got a sensor on the Stat housing....this one tells me exactly when the stat opens.

[mikeonb4c]

Yep....got a sensor on the Stat housing....this one tells me exactly when the stat opens.

Ah thats good To save me reading back through old threads, what are the temps either side of the stat at the point where it starts to open, and what is the corresponding top hose temp at that point?

[321Away]

Slightly late to join in!! I've seen this recently (yesterday!) on 2 very late aero diesels, the lower hose stayed cold even after long run (40+ miles) the guage showed normal and there was only minimal/normal pressure in the header, so flushed (as standard part of service), replaced stat with genuine part, and also rad on 1 car, fully bled and road tested both cars, EXACTLY the same result, everyting seems fine, guage/pressure/heater temp, but the lower hose dosent get hot, there is a minimal change in temp but not the usual hot, next thing to look at will be the pump??

Julian

[haydn callow]

321 Away...that does not suprise me at all and I suspect there is nothing wrong. At the last couple of meetings I have attended I checked the bottom hose of about a dozen Bongos as they arrived at reception (just stopped engine running) some had travelled 200 plus miles.....in all cases except 2 the bottom hose was cool.......after ticking over for a few mins the hose went hot.
In the other 2 cases they had ..a..been towing a heavy van...b..really "belting" along......this was in the summer.......During their journey I suspect the hose was getting hot on hills etc ....but when cruising along the engine did not require flow through the rad to keep temps down......

I also check every Bongo that visits my home.....same result

[mikeonb4c]

but might not airflow through the rad. when on the move result in a cool bottom hose anyway, even if coolant was flowing through the rad?

[haydn callow]

Well...see where you are coming from But......if that were the case the bottom would go hot the moment the vehicle came to rest (no rad cooling).......however it takes a few mins for the hose to go hot so this suggests to me that the bypass circuit soaks heat up when stationary and opens the stat.....it is the bypass circuit that operates the opening of the stat.

[mikeonb4c]

Well...see where you are coming from But......if that were the case the bottom would go hot the moment the vehicle came to rest (no rad cooling).......however it takes a few mins for the hose to go hot so this suggests to me that the bypass circuit soaks heat up when stationary and opens the stat.....it is the bypass circuit that operates the opening of the stat.

I guess it must be a combination of both. It would be most interesting to be able to continuously monitor temp and flow around the stat. etc.

[widdowson2008]

but might not airflow through the rad. when on the move result in a cool bottom hose anyway, even if coolant was flowing through the rad?

ABSOLUTELY - no 'might' about it.
The bottom hose should get warm anyway because of the ATF cooler in the bottom of the rad, even before coolant starts to flow through the bottom hose.

Ran a check on my temps this morning (accurately) and I generally agree with Haydn with the following rider:
In my opinion, all Bongos are slightly different and therefore the results will be different - the main difference being the condition of the sensor and its associated wiring.
My temps are taken using a TM-2 which is now fixed DIRECTLY to the head outlet (not the hose), so I am pretty confident with the readings.
Unlike Haydn's, my Micky Mouse Mazda gauge starts to move when the TM-2 reads 50C and reaches its 11 position at 65C (TM-2)

[haydn callow]

There will be quite a time lag between the actual Coolant temp and the bolt on the outlet stub plus the big terminal the sensor is in plus the epoxy the sensor is embedded in. Whilst you will get a pretty accurate reading there I think it will be substantialy delayed.

[mikeonb4c]

Slightly late to join in!! I've seen this recently (yesterday!) on 2 very late aero diesels, the lower hose stayed cold even after long run (40+ miles) the guage showed normal and there was only minimal/normal pressure in the header, so flushed (as standard part of service), replaced stat with genuine part, and also rad on 1 car, fully bled and road tested both cars, EXACTLY the same result, everyting seems fine, guage/pressure/heater temp, but the lower hose dosent get hot, there is a minimal change in temp but not the usual hot, next thing to look at will be the pump??

Julian

So many things might vary from Bongo to Bongo and, like Julian, I've always been particularly interested in (loss of) water pump efficiency/effectiveness, and, also, (loss of) radiator cooling efficiency, both of which might allow the coolant system to get into deficit, especially when a hot engine is suddenly changed from being on the move (good airflow through rad., pump turning faster) to a traffic jam (no airflow through rad. unless/until fans kick in, pump only turning slowly).

[haydn callow]

Surley all those things would make it run hotter/stat open more often..

'fraid that's my total imput to this thread

[mikeonb4c]

Surley all those things would make it run hotter/stat open more often..

'fraid that's my total imput to this thread

Of course, and thanks for gracing us with your presence. I was only reflecting on widdowson's statement:

In my opinion, all Bongos are slightly different and therefore the results will be different - the main difference being the condition of the sensor and its associated wiring.

I think a compromised cooling system could show its anger in many and varied ways: the one that strikes me as suspicious (when I read about it) is the mysterious boiling over of the (Bongo) expansion tank immediately upon stopping engine after a long run.

[widdowson2008]

There will be quite a time lag between the actual Coolant temp and the bolt on the outlet stub plus the big terminal the sensor is in plus the epoxy the sensor is embedded in. Whilst you will get a pretty accurate reading there I think it will be substantialy delayed.

Not the bolt, but the outlet stub itself. So I reckon it is about as near to the actual coolant temp as I can get without going into the flow itself, and not much of a delay either.