Digging an 84 FB out of 6 yrs of mothballs. She starts and the engine runs. I take it around the block to keep in moving. Took it about two miles this morning it got hot (for the nd time). Limped it home and it blow the top off the relief tank (2nd time again),

Bought coolant and a themostat yesterday. Was told to get a coolant pressure tester, presumably to see if the coolant system was leaking.

It doesn't seems to be leaking, just overheating. Where do I start?

 

What value does the temp gauge read?
Is the coolant boiling?

A bad internal water seal can cause exhaust pressure to pressurize the cooling system and the result can be the overflow tank being pressurized. This happened to me before. Take the rad cap off and start the car. See if there are tiny bubbles.

I new t-stat is a good idea but may not fix the issue.

 

Does that also cause 'overheating' or just 'overpressure'?

My water temp reading is way passed H.🤣🤣🤣

Boiling, I don't; I don't see boiling- but, it looks boiling hot.

 

The exhaust will not only pressurize the coolant but will boil it and overheat the engine.

 

A pressure test can help narrow down a bad seal. You can borrow a tester from the auto-parts store. Pressurize it to 20 psi and let it sit for 30 minutes to an hour. A bad seal is the worse outcome. Just giving some possibilities. Vary well could be a stuck t-stat. Lets hope so.

Overheating can cause the death of a rotary if sustained. So, don't drive the car until your pressure test is done or the t-stat is replaced. Mazda t-stat is the best. The t-stat hole sits at the top.

 

As KansasCityREPU stated, its definitely very important that the jiggle pin on the thermostat is at the 12 o'clock position when its installed. We've had issues with aftermarket thermostats here on the forum and most members recommend only using a Mazda thermostat and gasket.

 

Got a tester from the local parts store. I'm going to try to pressure test the coolant system of both cars tomorrow.

Also, put some MMO in the 85 FB that the piston mechanic (I think that's what I'm suppose to call him 🤣🤣&#129315, said had such a low compress (25 psi) that it needs to be rebuilt.

Rotary heads said use some MMO in the carb, turn the motor for 24 hrs, then give it a go. Tomorrow, I'm giving it a go.🥴

 

You'll want to clean and dry the spark plugs before attempting to start the engine after MMO has been put into the engine. If the engine starts, it will run rough initially and will smoke.....A LOT!!!!!! The smoke will last for some time, but don't be alarmed. Once the smoke clears and the engine is running ok, you will want to replace your spark plugs. This has been the path I've followed every time I've done an MMO treatment. You'll want to use the NGK BR8EQ-14 spark plugs.

Have you checked to make sure you have good spark and did you deflood the engine before putting the MMO in it or was it the other car that was flooding?

 

The mechanic did the de-flooding and cleaned and checked the plugs when they had it. The only thing done since was a tow and the intro of the MMO. I've hand-turned the motor three or four times since Tuesday night.

New plugs; roger that.

Lots of smoke, roger that.

Can I start it with the ignition key or do I HAVE to push start it?

 

if you can get it to start with the key, do it.

any engine makes more compression the faster you spin it, and the starter is ~250rpm, with a push start you can get it higher

 

Only asking because it hasn't been mentioned yet, but how's the fan running/working?

 

Fan is working.

Tried to turn turn it over. It did sound well.

Almost sounds like there wasn't enough battery to get it up and over, not sure.

I've got a video, but it's mp4 and the system won't take it.

Thoughts?

 

Pressure tested coolant system to thirteen psi for five minutes. There was pressure loss that settled at about 8 psi. I was unable to identify any leaks in the engine compartment and there was no fluid on the ground. Pictures attached.

 

If you pull the plugs with the cooling system pressurized can you hear air leaking into either housing?

 

I didn't try it at the time. Took the tool back. But, I'm buying an air compressor today, so I'll be able to replicate the test. I'll check to see if I can hear air escaping through the plug ports.

I've seen coolant test examples with a 'cool' engine running, and engine cold and off. Which should it be; or both?

 

engine off, not sure temp matters, it should hold ~15psi for hours, theoretically forever. i would go up to about 20psi and see what it does, more than that is probably not a great idea

 

Put in a new thermostat today.

Same result. Idles fine for about 12 min., then the temp goes up, quick.

Shut it off, remove the radiator cap and its a boiling cauldron. You can hear deep in the radiator the desperate gurgle.

I reckon I lose about a gallon and a half evey time.

No leaks in the engine bay that I can see.

What next?

 

If it lost that much coolant it has to be going somewhere. My guess, in the exhaust. Does the exhaust smell sweet?

 

...and, I should do what at this point?

 

If it's overheating and loosing coolant via the exhaust, time for a rebuild.

 

If you are losing that much coolant, its time for a rebuild. However, a gallon of coolant being consumed that quickly would cause the engine either to bog and to bellow white smoke as its being burned or what's not being burned will be in the exhaust system. Are you sure there's not an air pocket and that you are thinking you are losing coolant, when in fact you would have needed to burp the system and add more? Just spitballing.

Either way, its not a bad idea to get a coolant pressure tester and pressurize the system a little more and see if you can find the source of the leak by the means described above.

 

How would I go about creating a "burp" in the coolant system?

I can definitely hear leaking when I pressure test. It sounds like preasure leaking from something, and the system pressure is definitely dropping. But, I can't "see" any fluid on the block or ground.

I guess I could totally drain the coolant system to get an idea of how much is in it pre-test vs. how much it accepts on fill.

If I can't get the 'recommend daily allowance' in, then I'll know there is a blockage.

If I can get the amount of coolant recommended by Mazda back in the then I'll know its not a blockage, yes?

 

When you say it loses a gallon, how do you know this? If its when opening the hot radiator and it spews out, thats normal. You may have an air bubble. Burping the system needs to be done when filling with fluid. Heres the process:

1. Add coolant with radiator cap off until it appears full.
2. Squeeze bottom hose a few times until you see the level drop, and more coolant.
3. Repeat step 2 until you stop seeing the level drop in the open radiator. You should see a good flow of coolant past the opening in the radiator as it fillls.
4. Add coolant to the overflow bottle so that the tube is covered.
5. Cap radiator and let the system pressurize. You should see more coolant go into the overflow. When the engine cools you should see some get sucked back in. If it doesn't do that then the radiator cap is bad.

If you don't burp the system it won't have enough coolant and it will overheat.

 

I will attempt this today.

Thank you.

 

Did as you recommended.

Cap off, topped off, couple six good squeezes of the low radiator hose.

Fired it up with the cap off. Let it run for five minutes. Put a NEW radiator cap on, let it run at idle in the direct baking sun, for 15 min.

The temp never exceeded the half-way point.

Pick indicates temperature after fifteen minutes, before shut down.


Thoughts?