Antifreeze in Cylinder of 1990 Mazda B2200 and Other Issues

I’ll try to keep this short without omitting anything that might be pertinent. The truck was given to me by my stepdad. He had it about four months but only drove it every once in a while. It always started up and never ran hot, but something was not quite right, a rough idle and a bit of a missfire/momentary loss of gusto.

When my boyfriend and I changed the oil there appeared to be 6qts instead of the called for 4qts. We though someone had just gotten a little over eager with the oil. Anyway, he took a look at the spark plugs and changed them as they looked terrible (evidence of advanced timing/running lean/vacuum leak if I remember correctly). After the new plugs, adjusting the timing, the A/O mixture, and not finding a vacuum leak (I know that doesn’t necessarily mean there isn’t one) it sounded a bit better but something was still not quite right. We drove about 100 miles then took it to DEQ and, no surprise, we didn’t pass. He pulled the plugs again and all but one looked fine. Fast forward a week and he’s under the hood to replace the head gasket and antifreeze starts poring out of cylinder three (the same one with the sad looking plug).

From what I’ve read, at the very least the head gasket needs to be replaced (which we were doing anyways). I guess I’m just trying to find out if it could be something else instead or in addition. The confusing part is that the truck runs pretty darn good compared to other people’s cars that have had antifreeze in their cylinders. It doesn’t smoke, it starts up without hesitation every time, the temp gauge never even gets close to the halfway mark even after an 80 mile drive.

Any help/suggestions would be greatly appreciated.

Edited to add in case it matters: the check engine light is not lit after starting the truck.

Your boyfriend is a keeper,

Sounds like you’re on the right track.

You won’t know what the problem is until you get the cylinder head off. Maybe it’s just a failed head gasket, maybe there’s nothing wrong with the head gasket and there’s a crack in the cylinder head. Once you have the head off inspect the gasket, check or have the head checked for warpage and have it resurfaced as needed, and checked for cracks.

There’s also no guarantee that the truck will pass the DEQ even if the head gasket has failed and is replaced as necessary.

Anti-freeze in the cylinders can wash the rings and cylinder walls out which can then lead to oil consumption. There may be oil consumption even on the cylinders with no coolant in them.
Coolant diluted engine oil can also wash out crankshaft bearings, cam lobes, etc, etc.

I don’t know what your state does as far as emissions testing but there’s usually HC, CO, and NOX issues involved and anti-freeze may be only part of the problem.

Maybe a dry and wet compression test on cylinders that are anti-freeze free might be a good idea before tearing into this thing.

Put a straightedge on the block and the heads to check for warpage

I’m not sure about the exact specs for your truck, but you definitely want less than 0.005"

It might be a good idea to send the head out to a machine shop to be “cleaned up”

I highly recommend a new radiator cap and thermostat, as part of the repair

And make sure that radiator and hoses are in good shape

BTW . . . it is quite possible that your oxygen sensor(s) got contaminated . . . heads up

Thanks for all of your suggestions guys. After replacing every gasket the truck has - along with three valves, the fuel filter (the fuel pump had already been replaced), the oxygen sensor (thanks db4690), the ignition coil, a blown coolant hose, and a thorough cleaning of everything in between - the truck is running better but still not quite right. After reading an article on EGR valve symptoms (“The symptoms of a stuck open EGR valve are a rough idle with a lean air fuel mixture. The engine will behave as if it had a major vacuum leak.”) we pulled it and cleaned it. After re-installation the only change is that it now puts out black smoke, especially when you give it gas.

We are pretty stumped and there is not much info out there on diagnosing a vehicle that is sending mixed messages about A/O mix. Is there some sort of miscommunication in the system? A sensor malfunction? If so, who is the most likely culprit?

Again, any help is greatly appreciated.


Thanks for the update . . . it sounds like you made major progress

“puts out black smoke” . . . sounds like a rich mixture

Have you replaced that coolant temp sensor yet?

An EGR that is stuck open or being held open can cause an engine to belch black smoke so running lean is not always true.


Good to know. I cleaned it as best I could until the valve moved freely and no solvent was able to pass through from one chamber to the next when the valve was closed. Perhaps this was no enough and needs to be revisited as a possible culprit.


My first reply to you seems to have gotten lost…

Anyway. Yes, the thermostat was replaced today but he wanted to get after the mixture control solenoid before putting everything back together. After a bit more Google searching that came up as a pretty common problem with these trucks.