Ford Mustang Forums banner

1 - 20 of 24 Posts

·
Registered
Joined
·
89 Posts
Discussion Starter #1
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?
 

·
Registered
Joined
·
89 Posts
Discussion Starter #3
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.
 

·
Registered
Joined
·
3,064 Posts
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.
 

·
Premium Member
Joined
·
2,361 Posts
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.
 

·
Registered
Joined
·
89 Posts
Discussion Starter #6
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.
 

·
Registered
Joined
·
89 Posts
Discussion Starter #7
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.
 

·
Registered
Joined
·
586 Posts
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


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
89 Posts
Discussion Starter #9
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. I’d 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. I’m 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 doesn’t overheat. I’m stuck. Any idea’s.
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. I’m off today so will take it for a couple of hard drives.
 

·
Registered
Joined
·
89 Posts
Discussion Starter #10
3 hot/cold cycles today and everything is normal. Coolant goes into the overflow when hot, gets sucked back in when cold. I haven’t 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.
 

·
Registered
Joined
·
89 Posts
Discussion Starter #13
Update. The problem persists. I bought an airlift, but could only pull about 21 inches of vacuum where the instructions say to get it to 25 inches. Probably due to my small compressor not being strong enough.
I proceeded anyways but by the time vacuum ran out, I still needed to add about another 1/2 to 3/4 quart of coolant to top it. Went out and hooned for a bit, came back and coolant was bubbling again. #####
I hate to throw parts at this, but a t-stat is cheap and easy. Is there ANY possibility it could a partially malfunctioning t-stat?
 

·
Registered
Joined
·
21,853 Posts
Full procedure to fill coolant system with air lifts, jacks, Hills etc

Fill rad to only 1/2 level

Get it to operating temp, or higher, watch level drop, add accordingly and slowly

That’s it.

If you have air in the system after a few days of driving, its getting in there some how

Head gasket most likely
 

·
Registered
Joined
·
89 Posts
Discussion Starter #15
.....

If you have air in the system after a few days of driving, its getting in there some how

Head gasket most likely
Looking more and more like that except that darn Uview test is giving a negative result for gasses. Tomorrow I'll go out for a hard drive and come back and Uview test the bubbling overflow bottle (it's unpressurized).
 

·
Registered
Joined
·
89 Posts
Discussion Starter #16
I pulled the engine today, block is going to the machine shop to get tightened up.
While disassembling the top end I noticed no real issues. Throttle body to EGR gasket was pretty rough and the studs were next to impossible to get out and quite corroded. Maybe I had a small leak there that was causing the bubbling coolant.
Lots of folks were thinking head gasket. I pulled the heads and the gaskets had not failed. At least I don’t think so. Question:
Take a look at the pictures. Were these the right gaskets for these heads? They don’t have the little triangular holes that the block and the heads have. And it looks like coolant was trying to get through in those spots as the gaskets are bulged out in those spots. Maybe I was supposed to cut those parts of the gasket?
Stock E7’s with about 10k miles on the gaskets.
Thanks.
 

Attachments

·
Registered
Joined
·
3,867 Posts
So I assume that was it for you? I had a small leak once that took me 6-8 weeks to diagnose. Unfortunately by the time I did I had damaged my bearings and hurt my oil pressure.

Never again... possible HG issue and my heads are off in a jiffy.
 

·
Registered
Joined
·
89 Posts
Discussion Starter #20
I’m still not 100% sure. The gaskets looked fine. I was wondering why those little coolant holes were smaller on the gasket than the heads and block, but I read that is by design to make sure coolant gets around to all areas of the block.
At this point, I’m thinking it may have been a leak at the EGR. That gasket looked rough and the studs were really corroded.
 
1 - 20 of 24 Posts
Top