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Mazda Ed
Mazda Ed, ASE Certified Technician
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Experience:  ASE Certified Mazda Master Technician
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Mazda MPV LX After spending hundreds of $ fixing coolant leaks

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After spending hundreds of $ fixing coolant leaks I seem to have an coolant breach through one or more cylinders. My mech says the cooling system pressure is normal, but in heavy traffic I can hear the reservoir cap puffing to a rhythmic cadence that tells me there is definitely something strange. I can see the engine vibrate slightly but abnormally: the breached cylinder not firing properly? Last thing the mech did was loop the heater because the connections into the firewall were leaking (so he says, but I never saw that). We don’t need the heater over here, but is that THE solution? I feel my mech is milking the symptoms instead of fixing the problem.

Can this be diagnosed with the onboard computer as a cylinder misfire, lack of pressure or improper exhaust mix (or whatever, I’m not a car technician)?



What year is your MPV?

What size engine?


Customer: replied 6 years ago.
Year 2000
Engine V6
Mileage 122350

You can have a simple combustion gas test done on the coolant to find out if there is exhaust entering the coolant. Any competent mechanic should have the tool to do this. It involves a cylinder full of dyed liquid that is placed over the radiator cap. Then vapors from the radiator are sucked through the dye and if it changes colors there is exhaust gas entering the coolant. This could explain the multiple coolant leaks and puffing radiator cap.

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Customer: replied 6 years ago.
A simple test. Never done, my knowledge.

A follow up question: can a specific cylinder's lack of pressure be reported by the in board computer?
Customer: replied 6 years ago.
The test was never done. The mech says he doesn't even know what you're talking about. I will be referered to another mech who can diagnose the leak as a cover or block thing, or who knows.

I feel I have been dealing with incompetents. I will contact you on the "diagnosis". And maybe a lawyer afterwards.

Thanks for your prompt help.
The computer can recognize a misfire, but may not always report it right away. A good scan tool can read Mode 6 data which is where the misfire monitors are stored. There are counters in there that show how many times each cylinder has misfired. Before the check engine light ever comes on this data can be analyzed to see if a problem is about to occur or if an intermittent problem is occurring. A misfire can be caused by several things: A lack of pressure (compression), a fuel injector problem, a vacuum leak, or a spark problem to name a few of the most common.
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Customer: replied 6 years ago.
I suspect this has been going on for probably 2 years since the next to last yearly vehicle inspection said emissions did not pass, similar to today's scanner reading of Catalyst and EGR.

And after that the spark plugs were changed, supposedly. I suspect that the breached cyl spark plug should have looked, even smelled differently than the rest. Am I correct?

Customer: replied 6 years ago.
Got an estimate for the job. I'll try to translate the best I can. The lingo in Spanish can be very strange.

The main problem is the valve cover seals. The two valve covers look ok but will have to be "rectified" once they are removed. That alone costs $800. The "whole front" of the car needs to be disasembled, inc belts and the "chain". The valves need to be "rectified", also. New spark plugs (they may have gotten wet) and new cabling for the plugs is recommended. Those last two are only about three weeks old, can I keep them?

The job will be done in 2 weeks time and the total cost is $2,185, including $1,000 for labor.

Please advise. If this needs to be a new question let me know ASAP.
Customer: replied 6 years ago.
I uses the word "seals" but I think the right one would be "gaskets".

My RepairPal app on my iPhone says just replacing the gaskets would cost less than $500, inc labor.
Are they talking about valve stem seals???? That would be more along the lines of the cost and work described above. The valve cover seals (gaskets) are much easier to do than the valve stem seals. Either way that would not affect the cooling system so I'm not sure why they are giving this diagnosis.
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Customer: replied 6 years ago.
Frankly I dont recall the valve seals mentioned. I may have missed that because I don't know what they are. I never even got a written estimate. The workshop looked more like a pigpen-junk yard combination than anything. I'll bring the car back home while I inform myself better about the options in terms of costs and available shops.
Customer: replied 6 years ago.
Talked to the mech this morning. He says the gaskets are the issue but the valve covers usually go to the shop to be checked for warpage and integrity as they might be cracked. The valve stem seals are to be replaced. He repeated that the procedure requires him to take apart the whole car front, inc the tensors and chain (don't know the correct translation).

Seems I am getting the whole treatment, so to speak.

He never mentioned what happens if the valve covers are cracked.
Customer: replied 6 years ago.
Are valve stem seal replacement in this case a standard Mazda recommended procedure?

Just to be sure... There's a valve head? gasket and a valve cover gasket.

The trouble would be with the valve head's gasket, no?

I have a general idea but is there a diagram I can see?

Okay, he is talking about replacing the head gaskets which is a long involved process. You may be better off installing a used engine at this point. Especially if the heads are sent out and one or both are determined to be warped too much or cracked. Before anything is dismantled I would have the coolant checked for combustion gases... If this test comes back negative then there is no need to remove the heads or replace head gaskets.


Do a google search for LIS-75500 to see a picture of the tester and how cheap it is!


To see an example (not your engine) of the head gasket and other components see below:


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Customer: replied 6 years ago.
I’ll check on the LIS-75500 tester.

The MPV does not have a radiator cap, that I can remember. I’d use the reserve tank, no?

Not sure about the used engine. You actually think a whole used engine, plus installation, would be less expensive than the $2,200 plus the cracked head(s)?

Correct, you would use the tester in the reserve tank.


I can source you one from Canada starting around $350.00 + freight or one from the US for about $600.00 + freight. So it sure could turn out to be less... but again before we go this route get the coolant tested for combustion gases.

Customer: replied 6 years ago.
Had to order the tester because can't find it locally. Anyway, one of the prospects told me that a bubbling coolant reserve tank and the vapor out the muffler was evidence enough.

But I wonder if it might be an exhaust valve.

The cheaper ones uneaseme because I'm not sure yet what kind of shop they have or the ability to give any warranty. The cheapest one, so far, works for himself and says he could do the job for around $700 not inc any shop work with the head covers, which he said could be repaired even if found to have cracked. On Monday I'll be checking other mecs.
If you have heavy smoke out the tailpipe that smells sweet then that is an indication the engine is burning coolant. Do the vapors have any smell?
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Customer: replied 6 years ago.
I’m not sure it smells sweet, but it is vapor, not smoke.
Depending on temperature, how long the engine has run, time between running the engine, etc... there may be some vapors at times. Typically coolant in the cylinder will produce smoke and quite possibly lots of smoke! You can remove the spark plugs and use a scope to check the top of each piston, if you find one piston that is really clean compared to the others... that is from coolant burning in the heads. You can also examine the spark plugs for one that is very clean compared to the others.
Customer: replied 6 years ago.
At startup it will smoke or vapor more than while running. As long as I don't go up any hills the temp will show normal. The other day I was in a huge traffic jam and the temp never went beyond normal, even with the A/C full blast. Of course, the coolant was slowly vaporizing via the reserve canister and the muffler.

I expect a third mech to do on wednesday some tests and come up with an estimate.
Let me know what you find.
Customer: replied 6 years ago.
The latest mech tested all cylinders and found the front half OK. He says cyls #4 & 6 are the troubled ones. That's in the inside half of the engine. So, in theory, only one block gasket is gone. He will remove that head cover, send it to the shop for "rectification", replace the valve seals for $800.

He offered to change the distribution chain for an extra $300. I believe it's due for a change.

He's e-mailing me the estimate today.

I received the Lisle 75500 tester. I think it has enough fluid for several tests. I guess I should it test it now and after the repair?
You can probably do 10-15 tests with the amount of fluid provided. It wouldn't hurt to do one before and after the repairs so you can verify that it is fixed.
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Customer: replied 6 years ago.
A follow up:

I contracted the job with the last mech. Seems a serious guy. Last week I visited his shop and the motor top and front was already disassembled and ready for the head covers to go to the shop. The estimate went up and both covers will be done (of course). The job should be finished this week.

How much should the neutral switch set me back approximately?

I looked back through and don't see any talk about a neutral switch.... Is this for the MPV or a different vehicle you are working on?
Customer: replied 6 years ago.
Hello. It is for he Mazda MPV. My former mech told me he did not find anything suspicious with the neutral switch so he did not do anything about it. I bought a cheap scanner and the first thing in the list was a a P0705 or TRANSMISSION RANGE SWITCH MALFUNCTION. Incredible… he didn’t catch that at all.

The car would not start in Park. The would not start in ark nor Neutral. Now I have to insert the key and move the lever from Drive to Neutral while the key is in Start.

My present mech told me he would check on that.

To replace the switch by the book is a 1.1 hour job and the switch costs about 71.00


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Customer: replied 5 years ago.
Just wanted to report that the valve cover job was finished about a month and a half ago. So far, so good. I've driven a good 400+ miles sometimes going over 80 mph.

Thanks again for the excellent advise.
Glad you have a good running Mazda again!

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