Coolant overflow bottle cap blows off

This problem just started , every time I make a
Pass the coolant overflow bottle cap blows off .
I changed to a 17 pound cap and the same thing
Happens ,, I pressured up the system to 20 pounds
And there was no leaks . Anyone have thoughts on
What's going on ? Thanks

Head gasket

Thought about that , but there mls , guess it still could be

yeah, you're pressurizing your coolant system mr. Sort it now before you make another run and really f something up and it costs a bunch more than some gaskets.

I have had my 351c would do the same thing never would blow off until I ran the crap out of it or open it up wide open for a distance. I pressured the coolant system up to I blew a heater hose no leaks except water hose. Pulled the heads and didn't really see where it was leaking so I had my heads checked and they was fine put it back together and the problem was gone. We inspected the head gaskets super good and finally found just a very very small line from one of the cylinders to a water port after I put it back together.

Might try putting air to cylinders, and looking for bubbles in the water, just a thought. Good idea to fix problem ASAP.

Problem might not show up cold, try pressure testing it hot or warm. I had one that wouldn't show anything cold but we tested it warm it would show up. Good luck and X3 fix it before you run it!!!! Did you check the thermostat if it has one???? stuck closed????

69F100 wrote:Head gasket

What he said!!!

69F100 wrote: Head gasket.

X2. I concur.

I did a compression test and found #7 was
Low on compression so I pulled the head and
Seen where cylinder pressure was blowing in to the
Water jacket , also found a damaged piston with
A raised ring land , so I got the head checked and milled
.005 thousandths and using my extra piston to fix it.
I'm taking the nitrous off and changing the converter
To a motor converter , if anyone is looking for a nice
Converter check it out in the auction block section .

Glad you found it. Too bad on the skunked piston. I run a regular Felpro 1018 performance head gasket at 13:1 and I'm hitting it with the hose pretty good. Never had an issue. Maybe it's just dumb luck. It's your car but I'd try those before changing up the whole combo and ditching the nitrous.

The other head needs milled and found 1 more
Bad piston , I decided on replacing 5 pistons total
Picking the best 3 , gotta order 4 to get one more
Anyway . I found the top rings having a sharp edge
From some where like the nitrous cylinder pressure
Was forcing the ring against the cylinder wall .number
3 and 7 piston had the 2 ring pinched and top ring land
Raised at the intake valve pocket

Id be checkin the tune up on the thing if it did all that.

So does this combinaton of damage point more toward the nitrous being too fat combined with too much timming, or it being too lean in general?

Pretty sure it was fat , I don't think it was
A timing issue

How thick does a piston need to be at the intake
Valve pocket and ring land to be a good
Nitrous piston

10SHOTS wrote:Pretty sure it was fat , I don't think it was
A timing issue

I cannot answer your last question because I'm not an engine builder but I know running it fat on the hose is more dangerous to the health of the engine than lean according to the gurus.  The extra fuel tends to pile up on the.... wait for it.... ring lands... and blow the top/sides off the pistons.  Sounds like what you found unfortunately.  Do you have the details on your whole tune up?  I think there are dudes on here that could help prevent this from happening to you again.

I have personally never had this same experience. But I've melted holes thru pistons and made nice trenches in heads connecting 2 cylinders together in my younger days fooling with NOS before I really understood what I was doing incorrectly.  Aggressive timing was my issue.  Most of us have been there is all.

Big shot plate 104n--93f jets 5.25 fuel pressure 16.5 total
Timing , sonoco 116 max nos fuel 14.1 compression.
280-292 112 lobe sep cam 562 inch motor

Fat is bad, so is overtimed..... Both is really not good on stuff.

Fo sho not near enough jet spread w that tune, also what heads?

10SHOTS wrote:How thick does a piston need to be at the intake
Valve pocket and ring land to be a good
Nitrous piston

Good Nitrous piston, top ring land down .5" At .325" down, 1000 load, crushed em............

richter69 wrote:Fo sho not near enough jet spread w that tune, also what heads?

Trickflow 325 with c&c 80cc chambers , so your saying
I was pulling to much timing ? Everyone always was telling me
I couldn't never pull to much , I'm prob going back down to a 225 shot
How much spread and how much total timing do you think I need to start with
Thanks

May go back up to a 275  shot in time , that was a 95n 85f the 225
List a 82n 76 f ,  I was going use a 73f jet