Is this symptomatic of a thermostat stuck open (or missing)?

chrisvb · Post by **chrisvb** » Sat Oct 02, 2010 9:52 pm

Evening all,

Just need a quick reality check...

Today I graduated into Ye Grande Ancient Order of Bleeding Bongonauts having just done my very own full drain down, refill with fresh coolant and bleed.

2 questions have arisen...

Upon starting it from cold (and doing the whole funnel, see-saw, revving malarkey), I felt the bottom rad hose after only about 8 or 9 mins and it was already hot. I continued to bring it right up to temp for a further half an hour or so, all the while doing the revving thing (3 mins at 2.5k rpm followed by 1 min tickover... ish). During this time the temp gauge rose to around 30% and then just sat there on the button. So then I took it for a spin. After driving at about 30mph for a few mins the temp started to drop to around 5%. Whenever I now drive fast (40 to 80mph) the temp needle drops right off the scale to 0% - or more accurately about minus 10%. Then if I drive through London traffic again it goes back up to the 30% mark. The temperature of the engine seems to be governed by speed. Oh, and the heater seems very feeble (on the motorway). Am I correct in thinking that the problem is due to the thermostat either being stuck open (or even missing)!?

If the engine is running cold like this do I risk damaging it? Obviously I'll get round to fixing it sometime over the next couple of weeks but in the mean time is it safe to drive? At 30mph? At 80mph?

The other thing is, when I went to replace the coolant it came up to level (full) after I'd only put in about 8 litres. Should I have undone the nearside rad bottom hose when I drained down? Or is it sufficient to just undo the rad drain cock on the bottom offside?

Also, one last question - what are the thin pipes going into the bottom of the rad which, as I found out by accident when replacing a jubilee clip, contain oil? Is this some kind of engine oil cooling system?

Sorry if these questions are very elementary to some of you guys - as you can probably tell I'm willing but inexperienced when it comes to mechanics.

Many thanks in advance,

Ye Ancient Grande Bleeding Master

New Forest Terrier · Post by **New Forest Terrier** » Sat Oct 02, 2010 10:14 pm

Sounds awfully like a thermostat stuck open to me.

Southern Bongos are unlikely on general reputation to just remove the thermostat and hope no one realises.

I have run some of British Leylands finest with inadequate cooling systems without a thermostat in the summer and the effects sound similar. Nice cool running engine, but no heater. Stick thermostat back for the winter, heater again and carry on without any obvious problems.

No expert though and others will offer better advice.

wonkanoby · Post by **wonkanoby** » Sun Oct 03, 2010 6:33 am

the bottom cooler is for the auto box

haydn callow · Post by **haydn callow** » Sun Oct 03, 2010 9:43 am

To drain the system of the full 13 liters it contains when full,
Remove the Bottom hose from the rad......open the bleed pipe......remove the pipes from the rear heater.......remove the top hose from the rad......then.....flush water through all these "openings"........what you have done is left 6/7 liters of the old stuff in and now you have a unknown mix of coolants which is not a good idea.......I would start again...
Sounds as though the Stat is missing/faulty

haydn callow · Post by **haydn callow** » Sun Oct 03, 2010 9:46 am

Going back to your "other" topic re bleeding Shenanigans.....Now you have had a go perhaps things are making more sense.....
Bleeding is not something to take short cuts with.....

If you find no stat in there ask youself the question ..."why is it not there" Stat is often removed to cover some dark secrets

chrisvb · Post by **chrisvb** » Sun Oct 03, 2010 11:49 am

Thanks for the replies chaps.

My main concern is - is it safe to drive (for a week or 2) if running cool?

...and I'm not jumping to conclusions re the stat actually being missing. At this stage I doubt very much if it is - this was purely a hypothetical technical diagnosis not a reflection on the merits of the dealer I bought it from, who at this stage I have every reason to believe is an honest decent chap.

Cheers,

C

haydn callow · Post by **haydn callow** » Sun Oct 03, 2010 12:09 pm

I would not think any harm will be done running it cool but I would find out why and fix asap.

crazy uncle gray g · Post by **crazy uncle gray g** » Sun Oct 03, 2010 12:38 pm

Simple short answer to your question is YES

roofraisers · Post by **roofraisers** » Sun Oct 03, 2010 2:20 pm

When you say "the heaters are feeble", were they the same feebleness before you drained the coolant? If so & you are happy that you have got all of the air out of the cooling system then I see no problems in the next couple of weeks.

HOWEVER if the heaters were hotter before you drained the coolant, then it sounds to me as though you have an air lock in the heater matix or have managed to push some gunge/crap into the matrix resulting in poor coolant circulation. Both of these scenarios could lead to overheating the first being the air lock moving to the cylinder head..(plenty of topics on that) & the other that coolant isn't flowing around the system as designed therefore resulting in an inefficient cooling system.

One test you could do to maybe disprove the second paragraph is that after driving around & the thermostat is opening, park the Bongo with the engine ticking over & switch OFF all the cabin heaters. After 10 mins or so switch the cabin heaters ON & you should now notice hotter air.This is because the front radiator is now having no cooling effect as the vehicle is not moving & so the engine will get hotter & then over heat in time if no front radiator cooling fans switch on.

So in summary, I thinks if you are sure you got all the air out of the cooling system & the heaters are no worse than they were before you started this job .... you have little to worry about.
BUT if the amount of heat given off from the cabin heaters has changed.. then beware, trouble may be just around the corner if you continue to drive your Bongo.

Nigel

chrisvb · Post by **chrisvb** » Sun Oct 03, 2010 8:33 pm

roofraisers wrote:When you say "the heaters are feeble", were they the same feebleness before you drained the coolant? If so & you are happy that you have got all of the air out of the cooling system then I see no problems in the next couple of weeks.

HOWEVER if the heaters were hotter before you drained the coolant, then it sounds to me as though you have an air lock in the heater matix or have managed to push some gunge/crap into the matrix resulting in poor coolant circulation. Both of these scenarios could lead to overheating the first being the air lock moving to the cylinder head..(plenty of topics on that) & the other that coolant isn't flowing around the system as designed therefore resulting in an inefficient cooling system.

One test you could do to maybe disprove the second paragraph is that after driving around & the thermostat is opening, park the Bongo with the engine ticking over & switch OFF all the cabin heaters. After 10 mins or so switch the cabin heaters ON & you should now notice hotter air.This is because the front radiator is now having no cooling effect as the vehicle is not moving & so the engine will get hotter & then over heat in time if no front radiator cooling fans switch on.

So in summary, I thinks if you are sure you got all the air out of the cooling system & the heaters are no worse than they were before you started this job .... you have little to worry about.
BUT if the amount of heat given off from the cabin heaters has changed.. then beware, trouble may be just around the corner if you continue to drive your Bongo.

Nigel

Thanks for your concern and guidance Nigel - no the temperature of the heaters directly correlates with the rad temp which in turn correlates with the road/air speed. I'm confident I bled it effectively as even the next day after cooling overnight, the expansion tank level had only dropped about 7 or 8 mm according to my patent wooden spoon handle dipstick. In essence the heater has always (always meaning the last week, since I bought it) been ineffective and dependent upon road speed. Many thanks for the alert though.

Wonkanoby - thanks for demystifying the transmission fluid cooler hoses.

Haydn - Thanks for your usual thorough advice - very reassuring and useful, many thanks.

Crazy uncle gray g - good to get the definitive affirmative, cheers. You have a way with words!

It meant me and SWMBO could go out for a little jolly, beans on toast and a cup of tea in the pouring rain!

Chris

crazy uncle gray g · Post by **crazy uncle gray g** » Mon Oct 04, 2010 2:46 pm

I hope your beans on toast was enjoyable and your day out lovely,
but my response was to your question "Re: Is this symptomatic of a thermostat stuck open (or missing)?"
and my opinion & reply is still a resounding YES.

chrisvb · Post by **chrisvb** » Mon Oct 04, 2010 8:29 pm

crazy uncle gray g wrote: I hope your beans on toast was enjoyable and your day out lovely,
but my response was to your question "Re: Is this symptomatic of a thermostat stuck open (or missing)?"
and my opinion & reply is still a resounding YES.

My point precisely Uncle

I genuinely appreciated the resounding YES precisely because it meant I could shortcut the thorough explanations and just get on with my day... which I can confirm was lovely, and the beans were delightful!

Cheers fella,

Chris