Radiator Cap or something more serious??

[TheBocSez]

I have recently noticed that my temp is creeping up and that my gauge is showing reaching up to 240* then it will creep back down to the 200* area. Now for the 2nd time, I was cuising down the highway and POP coolant goes everywhere.

The 1st time, I figured I blew a hose so I pull over and pop the hood and discover the radiator cap had been blown off and is just laying in the engine compartment near the batt. I figured that maybe I just didnt put it on all the way, add coolant and put it back on. No issue.

Today, the exact same thing, so I no longer think that Its me not putting the cap on all the way. What would cause the radiator cap to just blow off?? Here is the back ground on the car.

Rebuilt shortblock 302
New water pump
new Motorcraft stock 192* thermostat
FRPP blue silicone hoses
Heater core bypassed
Heater tube removed, ECT sensor where metal tube used to attach, rear port plugged
about a 50/50 anti-freeze water mix with a bottle of water wetter
UD pulleys
Electric Volvo fan
Stock radiator

I checked the oil, no signs of water in the oil or oil in the coolant

Could it be as simple as the cap? or do I have a more serious matter I need to address?

Thanks for the help

 

[BadAndy]

I like the napa block tester, you fill it with fluid then put it in place of the rad cap, start the motor and with a pump thing you pull the rad gasses through the fluid and if the fluid turns color then carbonmonoxide is in your water system, - [see blown headgasket]-

 

[bill302]

try a new radiator cap i would think a hose would blow before the cap would blow off.... and post results...

 

[bill302]

another thing you can do is....try this fill rad. and crank motor without the radiator cap on, now do this with the engine cool see if you notice gasses exiting rad filler neck you can place your hand over the filler neck and see if gasses build pressure and blow past your hand (but be careful not to let water heat up and burn you this should only take a few seconds on a cool car)as if exhaust was entering cooling system.and sometimes you can even hear the exhaust entering the system thru the filler neck....post results....
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[TheBocSez]

Ill keep the results posted. I hate when you search threads and you find someone having the exact same issue as you, but they never post the results on how and if they cured it.

My current update, went out and added water while the engine was runnuing. Took 2.5 gal to fill it up. While filling, it would spit some of it out. Let it do this a few times until it stopped and topped it off.

I then went in the car and reved the engine pretty good a few times with the cap off. As soon as I let off, it was like old faithful, water came shooting out.

I filled it back up and put the cap on this time. Reved it up again and the cap didnt shoot off so I went to remove the cap (while the engine was running) to check the level, as soon as I started to move the cap, water started shooting out from under the cap.

Tightend it back up and here I am.

 

[HISSIN50]

Because of the way the cap secures to the radiator neck, it should NEVER be able to come off like that. I would be lookin for a bad flange on either the radiator or cap. This issue could account for the leak too.

Good luck.

 

[TheBocSez]

Because of the way the cap secures to the radiator neck, it should NEVER be able to come off like that. I would be lookin for a bad flange on either the radiator or cap. This issue could account for the leak too.

Good luck.

I was kinda thinking the same thing after doing a search. It is the stock radiator all though the cap is only about a year old. Probably a good time for a new radiator.

Is the spewing water normal?

 

[bill302]

so as you were filling the radiator gasses were exiting the filler neck so fast it would blow the water out....is this correct? and can you hear exhaust sounds coming out of the radiator neck if so i would suspect cracked head or head gasket....exhaust is entering your cooling system which is'nt good this would be my best guess without being there and with your descriptions.... and be very careful around this vehicle you can get burned or hit with the cap.....my son last year recieved 2nd degree burns in a similar situation.....i can't emphasize enough be careful......

 

[HISSIN50]

Some cars will shoot coolant out of the filler neck - and since you're purging air, it should happen.

Andy had a great idea with the cooling system tester (I dont know if parts stores loan them - were you two states west, you could borrow mine).

I have scuffed a radiator neck smooth before. I would really look hard at the curled edges of the cap (where they lock around the radiator filler) and the accompanying lip on the filler neck - something isnt holding the two together. The reason for this interface is just to keep the cap on there, even if the gasket failed or the spring in the cap failed and excessive pressure built up.

Each PSI in the system raises the boiling point ~3*F. That factored with the loss of coolant could account for the running hot.

It's kind of a crap shoot (if it's not the cap or radiator, you'll be saying 'crap! shoot!'). That's where the cooling system tester can really help out.

Good luck

 

[TheBocSez]

so as you were filling the radiator gasses were exiting the filler neck so fast it would blow the water out....is this correct? and can you hear exhaust sounds coming out of the radiator neck if so i would suspect cracked head or head gasket....exhaust is entering your cooling system which is'nt good this would be my best guess without being there and with your descriptions.... and be very careful around this vehicle you can get burned or hit with the cap.....my son last year recieved 2nd degree burns in a similar situation.....i can't emphasize enough be careful......

I dont think it was gasses and I cant hear any sounds. I think Hissin is correct in that since the system purged almost 3 gallons of coolant when the cap blew off, that most of the bubbling and purging was from air in the system.

I think Im gonna try that test kit from NAPA just to be safe, runs about 50.00 if remember right.

I did look at the filler neck and noticed that it was bent down some at the upper portion. I tried to straighten it out but I think Im going to invest in a new radiator and cap just to be safe.

 

[bill302]

good luck and keep us posted....

 

[TheBocSez]

Todays Update

Ok, drove it to work today, a small trip of about 3 miles. I noticed that about 2 miles into the drive, the temp gauge started climbing quickly to the 200-220 mark then leveled off. I could smell coolant so I just drove it nice and easy. Mind you, its about 430am and its fairly cool outside.

On the way home, I observed the same thing. Its about noon now and the temp is in the 90's. When I pulled into my driveway, I could hear a hissing sound and smell coolant. I popped the hood when I got home and could see steam and fluid escaping from the radiator cap/filler neck area.

The radiator is filled with mostly water at this point im sure and with todays observations, I am really leaning towards bad radiator or cap.

Any input?

 

[troyGT03]

check the coolant system with a pressure tester... i just had to change head gaskets because i was pushing combustion into the water jacket on one cyllinder. i also had no water/oil mix. but i have a boosted application.

 

[TheBocSez]

Well guys, I know this wont be much help for anyone experiencing a similar problem, but I replaced the radiator, Thermostat, and cap all at the same time. I went from a Motorcraft 192* to a 180* and now the car runs and idles at a constant 180-190 with no issue.

If I had to take a guess, I would say it was the cap or the radiator neck where the cap mounts as I could see the pressure escaping after a drive.

I tested the old and new thermostats, and both were opening fully.

Thanks for all the help.

 

[bill302]

great, and thanks for posting the final results....

 

[HISSIN50]

Agreed with Bill - thanks for sharing and we're glad to hear things are back to normal.

Time for a trans filter now.

 

[TheBocSez]

Agreed with Bill - thanks for sharing and we're glad to hear things are back to normal.

Time for a trans filter now.

Installing it now, only pain in the butt is trying to find a good spot in that tight compartment. I mounted it just below the power steering pump on the frame rail.

 

[HISSIN50]

The car I have in mind (for installing a remote filter) is a FWD - it should be even funner.

If you think of it, please shoot me a PM if anything unusual happens or you have to do something that wasnt intuitive. I'll be slapping the filter on and wont see the car again for a bit, so I wont get to do the usual inspections after a couple drives.

Take care.