Head or Gasket?

[bigdaddycain]

I have been quoted £1000 to get it fixed, or £1500 if it needs a new head (all plus VAT). Is that a reasonable price?

That's a reasonable price range that i've heard being bartered about a fair bit.

With your stat removed i assume that your top & bottom hose remain at pretty much the same temp under normal running? (with stat in place, top hose hot, bottom hose warm?)

Of course i stand to be corrected on this,but i'm guessing the placement of the stat in the location it is in factory form is where the mazda techies though best for the engine to reach full operating temperature in a reasonable amount of time, effectively the closed stat leaves 2/3 's of the complete cooling system to do its thing, (effectively aiding OT status quickly) Then, when the temp sensor senses 82c, the stat starts to open, giving the "full" range of cooling, by opening up the usually redundant 3rd of the rest of the cooling system... This is great if the temp sensor, stat are operating as they should be... The thing is, we that browse the forum regularly are quire aware that bongo's can have cooling related issues if a wary eye isn't kept on them... All it needs is a faulty temp sensor, or sticking stat to cause bigger issues. Does your average joe really know if the rad fans/stat opening procedure is actually taking place?

In my experience, removed stat causes slow OT status to be achieved, this can cover up issues elsewhere that need addressing... I suppose the question is,is it actually really necessary to have the stat fitted at all? The temp sensor (if working correctly) kicks the fans at a predetermined temp anyway, why only have 2/3rds of the system "online" 90% of the time if all the system being open is a more effective cooling system? (other than the initial quicker temp from cold start issue) I'm no expert by a long chalk on this subject,all the above may well be fundamentally flawed in it's concept.

[Aethelric]

I have been quoted £1000 to get it fixed, or £1500 if it needs a new head (all plus VAT). Is that a reasonable price?

That's a reasonable price range that i've heard being bartered about a fair bit.

With your stat removed i assume that your top & bottom hose remain at pretty much the same temp under normal running? (with stat in place, top hose hot, bottom hose warm?)

Of course i stand to be corrected on this,but i'm guessing the placement of the stat in the location it is in factory form is where the mazda techies though best for the engine to reach full operating temperature in a reasonable amount of time, effectively the closed stat leaves 2/3 's of the complete cooling system to do its thing, (effectively aiding OT status quickly) Then, when the temp sensor senses 82c, the stat starts to open, giving the "full" range of cooling, by opening up the usually redundant 3rd of the rest of the cooling system... This is great if the temp sensor, stat are operating as they should be... The thing is, we that browse the forum regularly are quire aware that bongo's can have cooling related issues if a wary eye isn't kept on them... All it needs is a faulty temp sensor, or sticking stat to cause bigger issues. Does your average joe really know if the rad fans/stat opening procedure is actually taking place?

In my experience, removed stat causes slow OT status to be achieved, this can cover up issues elsewhere that need addressing... I suppose the question is,is it actually really necessary to have the stat fitted at all? The temp sensor (if working correctly) kicks the fans at a predetermined temp anyway, why only have 2/3rds of the system "online" 90% of the time if all the system being open is a more effective cooling system? (other than the initial quicker temp from cold start issue) I'm no expert by a long chalk on this subject,all the above may well be fundamentally flawed in it's concept.

The fans have the greatest effect when the vehicle is stationary or moving slowly, at speed there is plenty of air coming in through the radiator to keep it cool. With the stat in place, the radiator does not contribute to the cooling until the coolant tremperature reaches 82C, then some cooled water from the rad joins the flow. From my experience running "statless" the radiator easily has sufficient cooling capacity to keep the temperature right down to "off the scale" even when motoring hard, as long as speed is maintained. I think that if FULL OT is achieved without a stat there is a problem elsewhere as that means the cooling system is running flat out, nothing in reserve, and its just coping.

BUT, my experiments are curtailed, as I now have developed a leak. "Ah" I thought, "I must have not tighted up the stat housing properly". But no, it's coming from the front of the engine so it look like the water pump. Now, I wonder if that is the way the air is getting in, and maybe the head is OK.???? Is there enough suck to pull air in? I guess if the sytem isn't pressurised (as in bleeding) the average pressure is atmospheric, so its above atmospheric on the outlet of the pump and below it on the inlet. Maybe that is where the air was getting in while I was trying to bleed the system. But after getting all the air out, replacing the expansion chamber cap, I did get more air in, with the stat in. I can see how the engine could pump air into the system but I'm not sure about the pump sucking it in. TGP, any ideas of the pressures we are talking about?

Strange how all this happened when I put the stat in.

Dave

[mikeonb4c]

Strange how all this happened when I put the stat in.

Dave

Might the positive pressure created when a thermostat was fitted and was closed (as when engine is cold) have put more strain on the pump/seal and tipped it over the edge?

[Aethelric]

Strange how all this happened when I put the stat in.

Dave

Might the positive pressure created when a thermostat was fitted and was closed (as when engine is cold) have put more strain on the pump/seal and tipped it over the edge?

That's possible Mike - that means I probably have a duff pump AND a head or gasket problem (i.e. why the stat was removed in the first place)

Dave

[mikeonb4c]

Strange how all this happened when I put the stat in.

Dave

Might the positive pressure created when a thermostat was fitted and was closed (as when engine is cold) have put more strain on the pump/seal and tipped it over the edge?

That's possible Mike - that means I probably have a duff pump AND a head or gasket problem (i.e. why the stat was removed in the first place)

Dave

Bummer I feel for you esp. as some git caused the first bit of trouble and obliged you to get a replacement Bongo. But, as I've learned in life (but forget sometimes to practice) 'nil bastardum carborundum'. It is what it is and its a case of having to move forward. With luck, all will come right and the bad days will recede into history. I remind myself of when my Spacewagon blew its ECU just after I'd been made redundant. £600 was required - like it or not - to put it back on the road so the family had transport. Somehow we managed it and its all distant history now.

Cars eh - who'd have 'em!

[The Great Pretender]

If the problem is air being drawn in, all it needs is for the negative side of the system to be slightly below atmospheric pressure Dave.
Mike maybe on the right trail about the stat.
If and it is just a guess fitting the stat causes the pump to 'pull' harder the negative pressure could increase drawing in more air.

[Aethelric]

Pump ordered. I can fit this myself, but I could not manage the head. If changing the pump fixes the original problem I'll be delighted and bloody amazed too. I will have to change the pump to be able to drive it the 35 miles to the garage to get the head tested.
If the pump was leaking before I changed the stat it wasn't obvious, now its losing coolant at an alarming rate.
How tight should the drive belts be?
Cheers
Dave

[missfixit70]

I think leaks on the water pump can be quite hard to spot if they're only leaking when it's under pressure & the engine's warm, as the water evaporates instantly, leaving no trace, fingers crosed it's just that easy
For the belt tension, I go with being able to put a 90 degree twist on the belt on the longest run, I think a 10mm deflection is quoted somewhere too.

[cheffy34]

Mike I tend to think of the engine as a radiator in a central heating system, feed and return pipes dropping below the rad same as the flow and return on the Bongo. Now any air that floats around the c/h system, when it gets to a radiator what happens, it rises to the top and there it stays and as more air works its way around it starts filling the radiator and normally the first you notice this is when the room is bloody cold.
Now if air gets drawn into the Bongo engine via air leaks or trapped air or a fresh coolant mix giving of air as it is heated. As the pipes have to drop down out of the engine bay the same as a radiator the air ends up in the same place, the top eg the head and there is stays until it is vented, make sense?
Now as the coolant in the head is being replaced by air the header tank level may not drop and this can carry on until the head is so full of air that the coolant level is below the level of the return hose to the rad and then no matter how fast the water pump spins it cant circulate, head heats up fast, fans come on, system presure rises, open the header cap and cool coolant is forced out.
Coolant being forced out of the header tank.............yer heads gone mate.
Heard that before?
So before commiting Harry Carry thinking the head is dead consider the simple things that can cause problems.
And remember.................Always look on the bright side of life.............

Excellent explanation - well worth noting by all as I think it explains the danger of relying on header tank level alone. It also suggests that temp measuring devices that rely on a sensor immersed in coolant could be fooled, so engine block sensor or (possibly) oil temp sensor might be better bets?

Ha haaaaaaa i'm back so if the header tank doesn't drop fluid what would be the best way to find out if the system is taking on air Mr P or is it a matter of going through the bleeding process which is no bother as mr P is coming down to devon to do mine for a glass of vino and a pint of chip fat

[Aethelric]

I think leaks on the water pump can be quite hard to spot if they're only leaking when it's under pressure & the engine's warm, as the water evaporates instantly, leaving no trace, fingers crosed it's just that easy
For the belt tension, I go with being able to put a 90 degree twist on the belt on the longest run, I think a 10mm deflection is quoted somewhere too.

Thanks Kirsty. Is that twisting or deflecting by hand?
Hopefully I should get the pump and fit it tomorrow. Then I try it out minus a stat and if it works I put the stat back and see if I still have a problem.

Dave

[missfixit70]

Yep, just by hand, good luck.

[Simon Jones]

Ha haaaaaaa i'm back so if the header tank doesn't drop fluid what would be the best way to find out if the system is taking on air Mr P or is it a matter of going through the bleeding process which is no bother as mr P is coming down to devon to do mine for a glass of vino and a pint of chip fat

From my experiences, if you are getting air into the system, the level of coolant in the expansion tank will rise to the point where it will come out of the overflow. There is the possibility that a coolant leak might mask this increase in level, but I'm sure it will become apparent once it has cooled down & the air contracted that the level will have dropped.

A thorough bleed using one of the recommended processes should get you back to the normal state. If air is still being introduced, then it will point to head gasket failure, faulty turbo or a pin-hole in a pipe somewhere.

[Aethelric]

Ha haaaaaaa i'm back so if the header tank doesn't drop fluid what would be the best way to find out if the system is taking on air Mr P or is it a matter of going through the bleeding process which is no bother as mr P is coming down to devon to do mine for a glass of vino and a pint of chip fat

.
Any air that gets is likely to end up in the cylinder head. If it were to end up in the header tank that would not be much of a problem. If it's in the engine it is displacing coolant so the coolant level in the expansion tank will rise. Best to measure changes when cold as it will rise when hot anyway. Good luck.

[The Great Pretender]

So Dave did you sort it?

[Aethelric]

So Dave did you sort it?

Not yet Mel. I can't do anything until I get the new waterpump. It was sent on Monday 7th by recorded delivery (usually takes 2-3 days they say) and thanks to the incredible Royal Mail service, there is no sign of it yet after 6 days. The Royal Mail says that current strikes will only effect London. I'm is Scotland so this must be the usual service. The Royal mail don't even see it as a problem until 15 working days following postage

I'll have to order another one on Monday, ensure its a courier service, and send one back when it finally turns up. Until then I'm a pedestrian
It's driving me nuts. It was god-awful weather when I was working on it in the street, now its fine but I don't have the part and I bet is raining again be the time I get it.

Rant over.

Dave