V6 Overheating - suspect water pump

[ThisIsTheSea]

Hi teenmal. Kind of. No hint of blue at all. Looked clear in the expansion tank. In the bucket it was translucent light brownish. Slightly see-through.

[teenmal]

If the radiator and heater matrix are OK (flow test)I would go for a sniffer test,they are not always 100% accurate,but it looks like excessive pressure in the system.What state were the water pump and the thermostat in.

[ThisIsTheSea]

Both pump and stat - apart from a slight brown film over the parts, not much different from new.

[Northern Bongolow]

Thank you windywatson and Northern Bongalow.

Not one to be defeated, I tried bleeding it again this eve (before reading your replies). I am following Haydn and Kirsty's video on Bongo bleeding. My V6 doesn't behave in the same way as the diesel does in the vid. When I increase revs, the coolant climbs up the funnel, whereas in the video the coolant moves down the funnel and into expansion tank.

Both radiator and exp tank caps are in good condition, but options are few at the moment so will definitely try that.

when your bleeding with the revs on and the funnel fills, does the exp tank empty or remain the same, if it empties this could be that the stats open-----this is what happens on a diesel when the stat opens, the revving fills the funnel. if the exp tank remains the same air maybe being (made internally) or there is local boiling internally.

i made a cap tester from an old exp tank fitted with a pressure gauge, this shows the pressure at which the cap blows.

[ThisIsTheSea]

Once the stat opens, the expansion tank drops quite quickly - I have to top up. I never let it fall below minimum. This coincides with the steam erupting from the funnel.

The thing is, if it was head gasket failure, surely I would be losing coolant? I'm not though. When system is pressurised, coolant level remains good and constant - it does not boil, drop or overflow.

[teenmal]

Once the stat opens, the expansion tank drops quite quickly - I have to top up. I never let it fall below minimum. This coincides with the steam erupting from the funnel.

The thing is, if it was head gasket failure, surely I would be losing coolant? I'm not though. When system is pressurised, coolant level remains good and constant - it does not boil, drop or overflow.

Do you know what the Actual engine/coolant temperature is running at or are you going with the original gauge.?

[Simon Jones]

First thing I would do is flush the system out and refill with decent antifreeze. You mention the coolant in the bucket had a brown tinge to it: this will be rust and sediment which is exactly what restricts the flow through the radiator and can then lead to overheating problems. In addition to reducing corrosion, antifreeze improves the thermal efficiency of the coolant and increases the boiling point.

[ThisIsTheSea]

Do you know what the Actual engine/coolant temperature is running at or are you going with the original gauge.?

Original gauge.

First thing I would do is flush the system out and refill with decent antifreeze. You mention the coolant in the bucket had a brown tinge to it: this will be rust and sediment which is exactly what restricts the flow through the radiator and can then lead to overheating problems. In addition to reducing corrosion, antifreeze improves the thermal efficiency of the coolant and increases the boiling point.

I have flushed through with a hose pipe. Nothing remarkable came out - was all clear. I have tried to get some idea of flow on the radiator. I disconnected the top and bottom hoses, put the hose pipe in the radiator filler, put my hand over the top hose inlet. The output from the bottom of the radiator is best described as a piddle. Not gushing out, but not trickling out either. Is this good enough? I suspect not, but difficult to tell as have never had a blocked rad on any vehicle before. What should it be?

[Simon Jones]

I seem to recall when I changed mine, I measured the amount of water it held which would be an indication of the volume of sediment. To do this, you need to start completely empty either by blowing it out using an air line, or sucking it out with a wet'n'dry vacuum cleaner. Block top & bottom outlets & then using a measuring jug, fill it via the filler cap neck at the top. I don't recall whether it was 1 or 2 litres, but it was exactly one of those values. Hopefully someone will have the exact figures for a genuine Mazda rad.

In terms of the dribble you are getting, that's probably fine as the water has to flow through the narrow water ways. If you poured a litre in the top (in one go) & it come out the same speed as it went in, then it would probably not be doing its job correctly.

[ThisIsTheSea]

Unfortunately I don't have an air line or a wet n dry vac at my disposal. If I fill the rad up with my hand over the bottom outlet and then take my hand off, it takes approx 1 minute 15 seconds to empty. That seems like too long.

[ThisIsTheSea]

Ordered a new rad this afternoon. I am almost certain that the rad has never been changed and it's a 15 year old Bongo, so a new one must be able to do some good to improve the circulation of the cooling system. There was some crud and scale inside the radiator filler neck, so that could be reflected elsewhere in the rad - although nothing came out when trying to flush it.

I will post an update once fitted and bled.

[windywatson]

Hi,

It is possible to get gasket leaks that pass more gases into the coolent system than they let water back into the cylinders. I would get the system pressure tested once you have the new rad fitted if that doesn't fix the problem.

Cheers

[ThisIsTheSea]

Thanks ww. TBH, if the new rad doesn't work I will be so pee'd off with it I may well be looking to get rid. Which would be a shame, as the bodywork is Ok and it's generally a very tidy Bongo.

What's the best way to get it to a Bongo garage without it overheating; run with a modified (or no) thermostat?

[windywatson]

If it is a genuine over heating problem, then running without stat would possibly do the trick. However if it is another fault such as combustion gases getting into the system then that would still show up if you run with stat removed so may actually help you with the fault finding.

Cheers

[ThisIsTheSea]

Yay - problem solved!!

I took the old radiator out this morning. Poured water in through the filler and it all ran out through the top inlet - nothing from the bottom. It took the easiest route of escape.

At lunch time the new radiator turned up. Flushed it with cold water, put my hand over bottom outlet, filled with water and then removed my hand and it drained in approx 8 seconds. A vast difference from the 1 minute 15 seconds I got with the old rad. Amazing. Fitted it, bled, 40 minute test run and it's as cool as a cucumber.

I didn't fork out for the genuine Mazda radiator - I bought the cheapest Chinese one I could find on eBay. Works fine. I'm happy.

Thanks to all that contributed advice and suggestions. So, so relieved that I've finally solved it!