jrussell

My question is, if the plugs are blowing from the rapid heat build-up inside the block, why isn't this problem also common on 1st and 2nd gen trucks. Maybe it is and I'm just not aware of it or maybe the freeze plugs are in different locations...not sure. Just a thought.

53 willys

So I just looked up the cooling system specs in our cummins manual....note this is for the 2nd genstyle 24v not the CR... but it should be pretty much the same..
here goes......

Measure the coolant at a coolant tap on the exhaust side of the the cylinder head.
RPM.............Location On Engine............Pressure
2000............Pump Out..........................14.2 psi
2000............1/2-NPT Head Port.............11.3 psi
2000............3/4-NPT Head Port.............12.1 psi
2500............Pump Out..........................23.1 psi
2500............1/2-NPT Head Port.............17.9 psi
2500............3/4-NPT Head Port.............19.4 psi

I don't know what to think the cause is of the blown plugs???even if you red lined it with the T-stat closed I would not think 30-35 psi would blow a plug out??? I get that number by comparing the two "pump out numbers" it looks like 10 psi for every 500 RPM???

dodgezilla04

i am not worried about any others popping. 99.9% of the folks whose plugs have blown, were only the rear one. i know that cummins went to a larger plug in the cr engines because they had some size issues. there are alot wilder bomber trucks than mine that are running only the rear plate or none at all.
mark, thanks for the research.

53 willys

I wounder if the head it's self is getting hot enough to expand slightly...allowing the plug to pop out??????
seems like the temp gauge would show that much heat??

Raspy

Good specs, nice find.

The pump head pressure is not added to the system. It's a differential across the pump. Not an addition to the overall system pressure.

The block is actually on the suction side of the pump. So I would expect a system pressure of 15 PSI in the block minus 1/2 pump head (15 PSI minus 1/2 of 14.2 at 2000 RPM) equals 6.1 PSI with the stat open. And a radiator pressure of 15 PSI plus 1/2 pump head. If the tstat is closed I would expect a block pressure of 15 PSI, and a pressure between the stat and the pump of 15 PSI plus pump head. Now add more heat than the cooling system can handle (because the stst is closed) and the pressure goes up, up, up. Pop goes the freeze plug.

The solution is more cooling immediately when the power goes up or an expansion tank to keep the pressure more stable.

When pressure goes up and up eventually a weak link will be found. The radiator top tank, a hose, or, in this case, the freeze plug. It seems like it would be something else, but plug appears to be the weak link. Higher pressure during racing should be a good thing to a certain extent because it raises the boiling point and prevents steam pockets. But the same thing will be achieved with cooler water and higher flow. The correct balance has not been reached yet. I can't stop thinking it's a thermostat delay problem most of all.

Wetspirit

53 willys

Forgot to add that those PSI's I listed above are with the t-stat open....

dodgezilla04

the plug in question is in the block, not the head mark.......

53 willys

I know...I was just showing what the Cummins specs show in the book....I can not find any pressure reading from the block....and the head pressure should be REALLY close to the same as the coolant passing by the cylinder walls, as they are the same port

now that the rear plug is blocked it will be the plug by the turbo next....Blackbeast blew his the next day after installing a rear block off plate
there has to be a better fix??????

Raspy

Blocking the rear plug is not really fixing anything. It's simply moving the problem somewhere else or ignoring it. It may be that there is a problem with the plug design or something, but extreme pressure will find another weak link. Until the pressure is controlled the problem will be there.

Wetspirit

53 willys

they had a note in the manual that said.....
Do not run the truck with out a t-stat it will cause over heating, the coolant takes the path of least resistance and will not flow through the radiator but the bypass hole in the t-sat housing.
weird most cars would never warm up if you ran with out a t-stat but the CTD is opposite???

Raspy

Interesting. It's gonna take some research and the time to take a few things apart to solve this.

Wetspirit

dodgezilla04

i think blackbeast's problem was not warming up enough before hammering it with all those mods of his.
I also did not fully warm up the same amount that i normally do.
besides the plug near the turbo is easy to fix compared to the one on the back. i am just gonna carry around a spare!!!!!

53 willys

do you have a part# for the plug you blew???

dodgezilla04

uh no, once it fit, i tossed the receipt. sorry.

53 willys

are you still going to post a PDF or something so we can print out a template to make a block off plate???please
Thanks