Bubbling coolant - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 12 Old 09-06-2019, 12:45 PM Thread Starter
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Bubbling coolant

I have a 5.0HO EFI (fox) swapped Miata. Been on the road for about 4 years...around 20k miles. A few small bugs to work out along the way, but mostly running good.
When I do track days (roadcourse lapping) after a hard run my coolant overflow container bubbles up and pukes out hot coolant. When car cools down overnight it sucks back in some of the coolant but not enough to fill the rad to the top. Car does not overheat or act weird otherwise. I pressure tested and changed rad cap. No change. I didn't believe it could be head gasket but bought the blue fluid test kit. Results show no combustion gasses. Car doesn't do this when street driving.
I'm kinda stumped on this. Any ideas?


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post #2 of 12 Old 09-06-2019, 01:25 PM
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What temps are you seeing on and off the track?


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post #3 of 12 Old 09-06-2019, 01:48 PM Thread Starter
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I don't have a true temp gauge, just the factory "dumb" gauge which reads normal. Fans kick on at 207* and they don't come on at the track (car is always moving), but do come on in stop and go traffic.

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post #4 of 12 Old 09-07-2019, 09:27 AM
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You will want to verify if the sending unit and gauge are compatible with each other, first. If they are accurate with each other and your coolant is not actually overheating, there's a possibility that the radiator cap is not holding pressure.

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post #5 of 12 Old 09-07-2019, 10:51 AM
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It can still be a head gasket. I have seen this on another car. Would only overheat if you drove the car over 100 miles. It would idle all day long no issues. It would go on a 60 mile drive no problems. Replace t-stats, radiator, fan clutch and on and on and it would still overheat after just over 100 mile drive. Replaced head gaskets and problem went away. Had a very, very small pinhole in the head gasket that took 100 mile drive to build up enough pressure in the cooling system to cause the radiator to overflow. Weird.

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post #6 of 12 Old 09-07-2019, 11:09 AM Thread Starter
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Quote:
Originally Posted by Saleen414 View Post
It can still be a head gasket. I have seen this on another car. Would only overheat if you drove the car over 100 miles. It would idle all day long no issues. It would go on a 60 mile drive no problems. Replace t-stats, radiator, fan clutch and on and on and it would still overheat after just over 100 mile drive. Replaced head gaskets and problem went away. Had a very, very small pinhole in the head gasket that took 100 mile drive to build up enough pressure in the cooling system to cause the radiator to overflow. Weird.
I considered that, and it's not off the table, but wouldn't the Uview test reveal combustion gasses even in this scenario?
I will have the top end apart over the winter to install some aluminum heads, but I'd like to confirm what this issue is beforehand.

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post #7 of 12 Old 09-07-2019, 11:11 AM Thread Starter
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Originally Posted by toddturbo View Post
You will want to verify if the sending unit and gauge are compatible with each other, first. If they are accurate with each other and your coolant is not actually overheating, there's a possibility that the radiator cap is not holding pressure.
Yup, using Miata sender and gauge. Tried 3 different caps over the last couple years.

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post #8 of 12 Old 09-08-2019, 03:08 PM
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Quote:
Originally Posted by MX8 View Post
I considered that, and it's not off the table, but wouldn't the Uview test reveal combustion gasses even in this scenario?

I will have the top end apart over the winter to install some aluminum heads, but I'd like to confirm what this issue is beforehand.


Not always. I had a similar issue and it took several attempts to get the Uview to show up


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post #9 of 12 Old 09-09-2019, 10:52 AM Thread Starter
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Some new info to add to help diagnose this. I wanted to run another uview combustion gas test, so with the rad cap off, I started the car to warm it up good first. Fluid kept rising up the filler, so I suctioned some out. Iíd give it a little throttle occasionally to help speed the warm up. I want to get it warm enough so the t-stat opens. I have to constantly remove rising fluid. Dash gauge finally shows normal, but t-stat remains closed. I ended up sucking out about 8 cups of coolant before i noticed coolant finally flowing, but it was still rising. I finally shut it off and the coolant immediately dropped. Literally instantly. Like whoosh the rad fill is empty. I filled it back up. It only took about 4 cups to fill. Iím going to take it for a short drive, let it cool down and check level again. Obviously it will be low again when I check it cool. This almost sounds like a stuck closed t-stat except the car doesnít overheat. Iím stuck. Any ideaís.
Oh, i did run the test again and the result was negative for combustion gasses. It does spit a bit of condensation from the exhaust, but from what i read that is pretty common.

edited to add
I did another couple hot/cool cycles yesterday. Each time it would take a little more coolant. This morning I checked and the rad was full and had sucked some coolant out of the overflow. Iím off today so will take it for a couple of hard drives.

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post #10 of 12 Old 09-09-2019, 06:03 PM Thread Starter
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3 hot/cold cycles today and everything is normal. Coolant goes into the overflow when hot, gets sucked back in when cold. I havenít had to add coolant today.
Maybe trapped air was in the system and it finally burped out? Track day on Wednesday will reveal all I guess.


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post #11 of 12 Old Yesterday, 07:16 PM
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Yes, trapped air. I've had issue just like yours. I now park the car with the front elevated & the cap off whenever I have had to add coolant.
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post #12 of 12 Old Yesterday, 11:06 PM Thread Starter
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Originally Posted by Stroked_93_Cobra View Post
Yes, trapped air. I've had issue just like yours. I now park the car with the front elevated & the cap off whenever I have had to add coolant.
Time to try an airlift i guess.
I didnít get to the track today due to bad weather.

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