Overheating problem

[chipvan]

is the garage you took it to a bongo friendly one? did they bleed it properly?

when you said over heated again..that bit worries me

will it not be under gaurentee?

[orielvilla]

Update.

Right then.

Over the last 3 months have had the following parts fitted. All brand new:

Cylinder Head
Main water hoses
Water Pump
Radiator
3, yes 3 thermostats.

The gargae just cannot get the thermostat to open during the bleeding process. They have even disconnected the fans but still no joy. The latest thermostat is a genuine mazda part.

Tomorrow the mechanic is going to remove the thermostat and see how it bleeds. I'm tempted to ask them to leave the stat out for good. I'm assuming it will take a little longer to get heat into the cab but so what? Can anybody see any problems with this or are there any suggestions as to what could be wrong?

Mechanic knows the pump is working and is convinced there are no blockages.

Help! Weather is getting warmer and I want to go fishing!

[wonkanoby]

the stat is the seal

so you could remove its innards but the ring bit is needed or it leaks

[Simon Jones]

Removing the thermostat (or the centre section) is generally considered to be a bodge done by dodgy selling who is trying to mask an overheating problem by making making the engine run cooler. Personally, I wouldn't do it.

Assuming the thermostat has been tested in pan of boiling water to check it is opening at the correct temperature, then it sounds like it is working fine. By removing it, it will take a lot longer to warm up which will increase fuel consumption as well as wear on the engine on gearbox due to the oil not being up to temperature.

How are they concluding it's not opening? The bottom hose does not ever get boiling hot (in my experience) but it should get warm when it opens. On my V6 the hose on the output of the thermostat housing currently runs at less than 20 degrees and recently is has hardly made it above single figures.

[Northern Bongolow]

tell him not to remove the stat.

when you bleed some bongo;s they airlock in the bottom hose, the one from the bottom rad to the steel link pipe back to the stat, get him to bleed the system with out running the engine, then crack the last connection pipe back to the stat housing, or even better loosen the 2 bolts that hold the 2 halves of the stat housing together until you get water. this bit of pipe should bleed ok through the jiggle pin but often needs help.
pm me if you need more info.

[orielvilla]

Once again some sound advice which I really do appreciate.

Air lock in the bottom hose sounds very likely and will ask them to follow your advice.

I'll update tomorrow. Fingers crossed.

[orielvilla]

Incredibly frustrated now!

Todays update.

Mechanic removed stat and bled.
Took it for a road test and everything stayed cold. Temp gauge never moved and heaters blew cold.

Left to cool down. Put new stat back in and bled cold including releasing air and water from the stat housing to ensure no air lock in the bottom hose. He felt it did bleed better after this new step and was hopeful.

Took on a 30 mile road trip. Three times the temp gauge shot up but also shot back down. This is erratic. Just as he returned to garage the heaters stopped blowing hot.

He's now thinking about putting in another stat (4th) but one that will open at a cooler temp. He remains convinced that the stat is not opening and the bottom hose staying cold. He has pressure tested the system so is confident of no leaks. Has also checked for exhaust gasses in the coolant and its clear.

He's also not sure if the fans are operating as they should. He felt they stayed on too long once it has cooled.

So thinking about renewing the temperature sensor and fan sensor switch.

I have taken one of the previous stats off him to test what temperature it operates at. The garage are still convinced its a stat problem but 3 new stats can't be wrong!

Any ideas out there.

[wonkanoby]

you must have a leak for the heater to stop like that

or he is not bleeding it right

[Simon Jones]

Back to basics: has he tested the thermostat? I assume they have a kettle as it sounds like there has been a lot of tea consumed by the mechanics or a saucepan and a hob to boil it on. Pop old and new 'stats in water and bring it to the boil. If they have a thermostat they can drop in the pan or better still an infra red digital one, then they can monitor the point where it opens.

[Northern Bongolow]

new head then new water pump fitted afterwards. this not fixing/finding the possible original cause of the first head failure may have contributed to a second head failure.

the reason he may think the stat is not opening/working maybe is that it isnt opening/working. the stat is not in the game because there is no flow around the system, the reason for no flow is an airlock. there are no leaks in the system so its making the air or its not been bled properly, if its been bled ok its making/leaking air via a crack in the head or gasket fault.
if the water pump had been replaced when the 1st head went things may have been different now.

sorry its just the way its sounding to me. hope im wrong.

[orielvilla]

I've tested the second new stat tonight. I noticed it start to open at 84 and was fully open by 95 degrees C.

So I know this stat is OK.

If we go with the worst case scenario of the new head failure, they have recently done a pressure test and checked for gasses in the coolant and both were ok.

With regards to flow around the system. He says he's removed various pipes to check for blockages and the coolant shoots out.

I'm going to return the good stat tomorrow but have no reason to believe the fitted original Mazda stat is defective. Maybe put both stats in a pan of water and compare?

I'm tempted to ask if I can assist with a bleed so I have peace of mind that it's being done correctly. I feel helpless at the moment.

Any ideas how much air it takes to block the heater matrix? And lets say you took out the heater matrix circuit, why wouldn't the remainer of the flow system work?

Am I right in thinking there are essentially three flow circuits? One around the engine, one around the heater systems front and back, and the other through the rad. If you blanked off the heating circuit (this is only theory) why wouldn't the other two work as they should?

Am I grasping at straws?

[wonkanoby]

have they flushed out the heater radiator,may be a big lump of crap moves around blocking it

[hammy67]

if the heater is blocked i would have thought the stat would have opened up sooner hence bringing the main cooling system via the radiator into play

[g8dhe]

Am I right in thinking there are essentially three flow circuits? One around the engine, one around the heater systems front and back, and the other through the rad. If you blanked off the heating circuit (this is only theory) why wouldn't the other two work as they should?

Try these links for pictures that Steve put together;
http://www.igmaynard.co.uk/bongo/forum/ ... 28#p520928
http://www.igmaynard.co.uk/bongo/forum/ ... 95#p515395
http://www.igmaynard.co.uk/bongo/forum/ ... 45#p462745
http://www.igmaynard.co.uk/bongo/forum/ ... 33#p445233
http://www.igmaynard.co.uk/bongo/forum/ ... 96#p435396
and there are many more use this search http://www.igmaynard.co.uk/bongo/forum/ ... 2008&ch=-1

[haydn callow]

It takes about 40 mins of tick over/revving to get the stat to open and the bottom hose to get. Hot