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Old 09-24-2016, 02:02 PM   #1
RustyWiring
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Default 31 AA Radiator Cap Blows Water at High RPM

Hello everyone.

I've been lurking on this incredible resource for a few months - since I purchased a 31 AA stakebed in April. I rebuilt the engine over the summer and am breaking it in now. So far, so good. 70 miles, 5-10 at a time, and only had to be towed home once early on! (my smoking distributor cried 'oil me, jerk!' but not before the points lobe melted away.)

Anyway, having little A experience, I thought to turn to the experts here with this issue: Motor is not hot but when I get the RPMs up, water blows out the radiator cap. I drop the RPMs, no blow over.

My cap seems loose to me; even for a non-pressurized system. There is a ratty, red gum seal in there but it makes little-to-no contact with the cap when rotated tight. At times, the cap even rotates a small amount (~10 degrees) while driving.

Is that sort of aggressive water flow normal?
Does the closed radiator cap need to be snug/sealed?
Should I get a new cap?

{Thanks to all of you for your generous insights on this board. I was able to anticipate several issues during rebuild because of reading the 'barn. For instance, when the engine didn't want to fit back in, instead of cursing, I remembered reading here that that happens and to spread the frame. Used a bottle jack and 4x4 and in she slipped.}
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Old 09-24-2016, 02:12 PM   #2
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

Sounds like you need a new gasket for the cap http://parts.modelastore.com/show_Product.asp?ID=3751
Also make sure the radiator is not over full, coolant should just cover the tubes.

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Old 09-24-2016, 02:31 PM   #3
RustyWiring
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

Thanks Bob.

I noticed that that gasket you linked says 'not for quails and motometers'. I have a motometer.

The radiator WAS filled pretty much to the top. That's no longer case
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Old 09-24-2016, 02:34 PM   #4
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

I used an oring from my universal HF oring kit that works good on my motometer
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Old 09-24-2016, 02:46 PM   #5
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

Ha! Great suggestion, Mitch. I have that kit in my barn
Love those $0 solutions (and so does my wife, who curiously asked the day "You can sell it for more money now, right?")
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Old 09-24-2016, 02:49 PM   #6
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

I forget which kit it was the standard or the metric... I believe there was one in each kit that worked but one was better than the other..
Good Luck

Last edited by Mitch//pa; 09-24-2016 at 03:03 PM.
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Old 09-24-2016, 04:34 PM   #7
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

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Originally Posted by RustyWiring View Post
Hello everyone.

I've been lurking on this incredible resource for a few months - since I purchased a 31 AA stakebed in April. I rebuilt the engine over the summer and am breaking it in now. So far, so good. 70 miles, 5-10 at a time, and only had to be towed home once early on! (my smoking distributor cried 'oil me, jerk!' but not before the points lobe melted away.)

Anyway, having little A experience, I thought to turn to the experts here with this issue: Motor is not hot but when I get the RPMs up, water blows out the radiator cap. I drop the RPMs, no blow over.

My cap seems loose to me; even for a non-pressurized system. There is a ratty, red gum seal in there but it makes little-to-no contact with the cap when rotated tight. At times, the cap even rotates a small amount (~10 degrees) while driving.

Is that sort of aggressive water flow normal?
Does the closed radiator cap need to be snug/sealed?
Should I get a new cap?

{Thanks to all of you for your generous insights on this board. I was able to anticipate several issues during rebuild because of reading the 'barn. For instance, when the engine didn't want to fit back in, instead of cursing, I remembered reading here that that happens and to spread the frame. Used a bottle jack and 4x4 and in she slipped.}
Sounds like the classic leaking head gasket. As long as the engine is doing light work it is happy. As soon as the engine is working harder the cylinder pressure increases and the hot gasses bypass the head gasket and boil the radiator. Forget looking for water in the oil, the hot gas only exits through the water jacket when the pressure rises. Try retorquing the head. Also as mentioned seal the radiator cap and adjust the water level. Rainmaker Ron
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Old 09-24-2016, 05:02 PM   #8
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

The radiator should have a baffle, see the photos of the baffle in post #2 in the below thread.

http://fordbarn.com/forum/showthread.php?t=165125
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Old 09-24-2016, 06:02 PM   #9
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

@160B: I don't think that there is a baffle as I can look right down to the core.

@Ron: That thought occurred to me but I had suppressed it . I got the copper-clad gasket from Snyders and copper sprayed both sides prior to assembly. The head nuts are torqued properly but I'll recheck. One bolt by #3 on the intake side stripped and I heli-coiled it. That nut is torqued to 45lbs rather than 55lbs like the others. However, a bolt between #1 & #2 had antifreeze leaking up on to the top of the head. It happened when it first ran - two weeks ago, leaked a few runs and now has appeared to stop. That made me wonder if I had a cracked head. The compression in #2 is also much lower than the other three, which are locked in around 60lbs.

Oil is good - no foam or droplets. Plugs are good - no fouling. No smoke out the back. No sweet smell of antifreeze in the exhaust. Plenty of power to roll along at 40MPH...although I might need the wiper on when the geyser hits.

Do these observations change any diagnoses?
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Old 09-24-2016, 06:28 PM   #10
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

Call me a liar - twice.

I have a baffle. I can see the core ON EITHER SIDE OF IT. It baffles the upper inlet from the pump.

Rechecked the head nut torques - 75% of them were below 55. They are snug now.

I guess I'll reset and try again tomorrow.

(Still worried about low #2 compression and that yellow-green crust on the nut between #1 & #2 spark plugs)
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Old 09-24-2016, 07:37 PM   #11
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

you should be doing serial re-torquing every 25-50 miles for a couple hundred miles
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Old 09-24-2016, 08:29 PM   #12
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

I found on mine that I needed to torque it several times early on until it settled in at 55 lbs. I still check mine at least once and usually twice a year. You can not torque it too often as long as you stay at 55 lbs.
I would however torque the one with the helicoil the same as the others. It should be strong enough.
What is the compression for each of the cylinders?
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Old 09-24-2016, 09:30 PM   #13
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

yep a properly done helicoil is as strong as what it replaced
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Old 09-25-2016, 08:46 AM   #14
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

Sometimes it's better just to run a NEW, original type cap, to seal it up properly!
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Old 09-25-2016, 08:58 AM   #15
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

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yep a properly done helicoil is as strong as what it replaced
Used to put them in the old Volkswagen engine cases for the cylinder bolts. Once they were Helicoiled they were much stronger than the original thread. That was in aluminum of course.
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Old 09-25-2016, 10:25 AM   #16
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

Well, I re-torqued, sealed the cap with an o-ring so that it was nice and snug and... blow over. It's coming out the bottom of the cap assembly, where it fastens to the radiator mouth.

I've noticed that it seems to occur before the engine has been running for more than, say, five or ten minutes. Also, it seems to blow under load - like going up a hill. I can keep the RPM's up going downhill but get no blow over.

So, I am leaning toward either a bad gasket or (don't tell my wife ) a bad head. The engine warms up, expands in certain places and the blow over stops.

Any insights folks? Bite the bullet and replace them both?

@All: Thanks for the information on heli-coil. It's at 55, like the rest.
@1Crosscut: The compression in 1, 3 & 4 is right around 60lbs. In 2, it is in the single digits. I didn't check it before I put the engine in and that's on me. That's what makes me think the gasket or head is ruined (and the machinist said the decked head was fine but I didn't ask him to magnaflux it). Maybe valves but they seated great as I lashed them.
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Old 09-25-2016, 10:35 AM   #17
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

Have you been retorquing the head when the engine was hot? If so, it is not the torque settings but a problem with the head or head gasket. You will need to pull the head. You will be able to see if the head gasket has a break in it. If not, you will need to have the head magnafluxed. If your head is not worth fixing, I recommend you replace it with a Snyders 5.5 head. JMO
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Old 09-25-2016, 11:10 AM   #18
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

Quote:
Originally Posted by RustyWiring View Post
Well, I re-torqued, sealed the cap with an o-ring so that it was nice and snug and... blow over. It's coming out the bottom of the cap assembly, where it fastens to the radiator mouth.

I've noticed that it seems to occur before the engine has been running for more than, say, five or ten minutes. Also, it seems to blow under load - like going up a hill. I can keep the RPM's up going downhill but get no blow over.

So, I am leaning toward either a bad gasket or (don't tell my wife ) a bad head. The engine warms up, expands in certain places and the blow over stops.

Any insights folks? Bite the bullet and replace them both?

@All: Thanks for the information on heli-coil. It's at 55, like the rest.
@1Crosscut: The compression in 1, 3 & 4 is right around 60lbs. In 2, it is in the single digits. I didn't check it before I put the engine in and that's on me. That's what makes me think the gasket or head is ruined (and the machinist said the decked head was fine but I didn't ask him to magnaflux it). Maybe valves but they seated great as I lashed them.
You can learn more with the head on than pulling it off. Leaky head gaskets do not have a blown out spot that is visible, in fact there will hardly be a discoloration. Something about single digits compression does not sound right, Are you sure it measures less than 10 lbs? Make sure you are getting the right info from your tests. Lock and block the wheels and put a load on the engine in High gear while watching for the radiator to erupt. You may need to do a leakdown test to find the problem. In any case unless you have a large visible crack in the head you will see nothing to give you a clue with the head off. Rainmaker Ron
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Old 09-25-2016, 12:26 PM   #19
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

@Dick: I torque when it's cool (thanks to reading the 'barn) but have only torqued three times in the 100 miles it now has on it.

@Ron: I will recheck compression. When I did it two weeks ago, it was 2-3lbs. I checked 1, then 2, scratched my head, did 3 & 4 and retested 2 and still got virtually no reading on the guage. 58-60 on the other three cylinders. I checked the head when I got it back from the shop - there were two hairlines about a half inch long around one the the bolt holes (probably the one that leaked early on). The machinist said he'd ignore them. I can't imagine all the compression would exit there without first registering something greater than 3lbs. Seems more and more like I screwed up the gasket installation.

So, now I'll set the compressor to 10# and grommet the air line to the #2 spark plug hole and listen/watch for where it goes.
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Old 09-25-2016, 01:35 PM   #20
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Default Re: 31 AA Radiator Cap Blows Water at High RPM

if you e got single digits id guess you got a major crack or non sealing valve. A leakdown test will tell you everything there is to know.
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