Expansion tank

I would also recommend that you place your fill tank with pressure cap so that the line from the fill/pressure tank connects to the system at the suction side of the pump. This will set the point of zero pressure change in the system and insure proper operation of pressure cap. This is not as important with a constant flow electric pump as it is with a mechanical pump but still recommended.

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<!-- google_ad_section_start(weight=ignore) -->Mike Trusty

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I saw this quote on a recent thread which made me wonder if this was the reason for my expansion tank failure 2 days ago in which a welded seam burst. After r&r coolant and purging all the air from the system the motor ran cool for 40 freeway miles. Shortly after exiting the freeway the tank burst.

I had surmised that due to excessive steam build up during my bleeding procedure of the water system I must have initiated a crack in the expansion tank.

Down stream from the manifold \ thermostat is where my expansion tank feeds into the radiator return line (I use a mechanical water pump).

1) Is there pressure into my expansion tank using this location?

2) How does locaton of the fill line affect the operation of the pressure cap?

3) Would the location of my fill line be the reason the initiated crack devoloped further?

4) My pressure cap is 20#, is that too high?

Tim

i have similar questions in my post here
http://www.gt40s.com/forum/gt40-build-logs/24525-toms-rcr-40-trackracer-18.html#post281962
My fill line ( or expansion line) from the expansion tank feeds into 1 of the 5/8 connections on the suction side of the water pump.
Concerning the presusse my understanding is still, that in a closed system with a given pressure this pressure is the same everywhere in the system.
The only thing i could think of that the pressure on the outlet side of the waterpump is higher , is due to the backpressure build by the system following afterwards ( engine , thermostate,<=you have connected in right here if read correctly=> feed line, radiator, return line ). THis assuming the water pump is able to create a additional pressure. Which could not be much due to the design as a circular pump ( it is not a positive displacement pump)
From the components mentioned above, the engine probably creates the biggest pressure drop and therefore the biggest backpressure.
So after the thermostat there should not be much additional pressure anymore.
Of course on the suction side it will be a little lower but in my opinion not as significant to blow your expansion tank before your pressure cap releases.

Was it a selfmade tank or a pruchased one? My assumption would be a tired weld.

TOM

Was it a selfmade tank or a pruchased one? My assumption would be a tired weld.

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Tom,
Yes, self made. My fabricator contributes the failure to fatigue. Repeated expanding\contracting of the metal tank possibly due to the pressure relief cap not working properly.

Thanks a million for the input regarding the fill line. I am taking the suggestion to move the line to the suction side of the water pump, can't hurt and appears to be the correct location over what I currently have.

20 PSI is an awful lot of pressure to carry in such a large system.

Why so much pressure?

My plans are to stick with a 13# system as it's always worked well for me and that brings plain water to about 245F boiling point. I rarely use just water though - generally at least 20% antifreeze. This brings me to ~250F to my past calculations.

Pressure and Boiling Points of Water

RE: Position in cooling system circuit
I think having your coolant reservoir on the suction side of the pump is key - else it will see surges coming from any air entrained in the coolant.
Older Corvettes were all done this way and I've plumbed a number of other cars this way with no troubles.
Still somewhat perplexed as to how I'll do it with my remote water pump though.. I'm not beaten yet!

20 PSI is an awful lot of pressure to carry in such a large system.

Why so much pressure?

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Live and learn Randy :stunned:. Been running this cap for the past year and 20 psi has not been a problem up 'til now. Per the recommendations here, I am certainly going to reduce it :thumbsup:

Frankly I had been wondering why my puke tank never had any moisture in it :inquisitive: !!

i was running about 13psi, but changed it to 21psi on the recomendation from here. Has this now changed?

Richard

was there any issue with the 13# system ?

TOM

I believe most "modern" coolant systems will use a cap between 13 to 15 psi to boost the boiling point and use a thermostat of about 200 F. If your having overheating with this starting point combination, maybe go with a higher pressure cap and/or lower T-stat. Just my "rule-of-thumb" 2-cents. Also, I've found that ceramic coating the exhaust will help a little (probably by decreasing the engine compartment temps).

EGLITOM said:

Richard

was there any issue with the 13# system ?

TOM

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not sure - it was pumping out about a half a litre to one litre of water on a trip - but it still seems to do that with the 21psi cap as well. It seems as though the header tank isnt capable of containing the expansion of the water. I might be fitting a secondary expansion tank in the future to ensure that the excess water is not lost, but sucked back when the system cools. At the moment, I have a motorbike expansion tank just strapped to the header tank and that works fairly well - just doesnt look very nice .