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sprinkles08, ASE Certified Technician
Category: Car
Satisfied Customers: 23116
Experience:  ASE Master and Advanced level certified. Factory trained with 17 years dealership experience
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I have a Mazda Bongo (2.5l Diesel) that has cooling issues. It has bl

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I have a Mazda Bongo (2.5l Diesel) that has cooling issues. It has blown two radiators in a 3.5 year period, and is losing coolant much more rapidly that I'd expect, and has overheated in the past. I've had it pressure tested and also sniff tested, which showed no fault (no exhaust gas in the water, no oil in water or water in oil). Any guess as to what the problem might be, and what should be done next to find / fix the fault?
Is it possible that the tests I've mentioned could have failed to detect a major defect in the cooling system?

Hello and welcome to JustAnswer!


I'm not sure exactly what type of test you did to check for exhaust gases in the cooling system, but the best way is with a Block Test kit. This kit uses a vial placed over the radiator cap opening and you pour in a blue liquid and then run the engine. If there are combustion gases in the cooling system then the blue liquid will start to turn yellow.


If you're losing coolant then it either has to be burning inside the engine or leaking externally. If there are no leaks external then it has to be going inside the engine. If that's the case then that could be the reason for the radiator failures also. If the cooling system is over pressurizing or it is overheating then it can be causing the radiator issues.


Another thing that can be done is apply air to each cylinder with the engine cold and radiator cap off and see if bubbles appear in the coolant. If bubbles appear then you know for sure that you have a head, headgasket or block issue.

Customer: replied 4 years ago.



Sorry if my questions seem a little odd - this actually relates to a dispute between a customer and a dealer, and what I'm trying to do is get an independent opinion without biasing you one way or the other. The engine issue itself has since been resolved - I'm trying to establish what kind of tests would be needed to detect the problem


The first overheating and radiator replacement occurred a couple of years (and a few thousand miles) prior to the customer buying the vehicle. The dealer did not inform the customer of this prior to purchase.


The tests the dealer did after the 2nd overheating & radiator rupture were these:

  1. Pressure test (exact details not known, but conclusion was no leaks present)

  2. "Sniffer test" (again, no detailed report is available, but they concluded no oil in water, no water in oil, no exhaust gasses in water)


They concluded from this that the problem was an air-lock in the system, and said the van was performing as normal.

A short time after this there was another overheating incident, and a different garage confirmed the head gasket had failed, with a "bubble test". They stripped the engine and found the actual failure was caused by the cylinder head leaking through No3 exhaust port, which ultimately caused long-term damage to the head and gasket .

The crucial question is, could the original leak have gone undetected by those two tests the dealer carried out? They are claiming that all the damage occurred after they returned the van to the customer, and their argument is that the negative tests prove this, although it should be noted there's no documentary proof of the tests themselves.

I'd like to know if you agree with their position, or if you feel they could have gone further in diagnosing the problem

I'd also like your opinion as to whether this sounds like a sudden, short term problem, or something that would have built up gradually over time.

Many thanks

Chris Gatland


It's definitely possible that the root cause went undetected for the couple thousand miles. I'm not exactly sure what they're referring to when they say sniffer test, the normal test to check for exhaust gases in the cooling system would be with the fluid kit that I mentioned. Either way, if the test wasn't done properly then there could have been an internal leak at that time and it wasn't properly diagnosed.

It's also completely possible that the first overheating episode is what caused the head to crack. If the radiator ruptured and the engine overheated at that time there may not have originally been a head issue but a crack started to develop because of that. It likely developed and got worse as time went on.

I'd say the probability would be about 50/50, the original problem undetected versus the original overheating causing the head to crack.
Customer: replied 4 years ago.

Okay so just to clarify what you mean by "50/50", are you saying you believe that one of those two outcomes definitely did occur? ie either:


1) The leak was there long-term, but was not detected by the tests the dealer carried out (for whatever reason), resulting in the eventual head damage


2) The head damage occurred at the original overheating, implying presumably that the dealer deliberately turned a blind eye to what must have been obvious damage


Please correct me if that's not the correct interpretation. Thanks again.

That's correct. The probability is about 50/50 that either the problem was not diagnosed correctly the first time and the head issue was there all along, or the head issue could have been caused when it overheated the first time.
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Customer: replied 4 years ago.

Hi again!


I'm now in the process of preparing my case against the dealer regarding this engine issue, and I'm hoping to submit your advice as an expert witness statement. Would you be willing to complete a short statement and send it to me? I will pre-prepare a template in the correct format, so hopefully it'll be a simple case of pasting in your comments, signing and dating the form and posting it to me. Of course, I'll happily add a bonus to your account to cover your costs and time!


If you're happy to do this, could you first reply to this message with your name, background and short summary of qualifications? I will need to submit these details to the court to ask permission to use your statement.


Many thanks!




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