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To be clear, I work in round numbers and whereas I cannot remember the exact dimensions of the expansion tank, I am assuming that it is about 10 inches in diameter [maximum]- probably a bit optimistic but serves to make the point- such being the case the cross sectional area would be about 80 sq inches x 15 psi = 1200 lbs force trying to rip the seam apart. If the thing happens to be a bit smaller in diameter say about 8 inches in diameter there would still be 800 lbs force trying to rip it apart.
That is exactly how it works.
Nope.
And that's not what the cooling system is.
And the..."sum" of ever square inch of pressure means entirely nothing.
That's why the spring on the radiator cap says about 1bar, and not 68bar.
And the..."sum" of ever square inch of pressure means entirely nothing.
That's why the spring on the radiator cap says about 1bar, and not 68bar.
Jeff,
The cooling system is most certainly a pressure containment system consisting of a number of components each of which has to constrain the forces generated by pressurisation. The expansion tank is just one such item but so are the block, the cylinder head, the water pump, the radiator and the heater matrix not to mention the various hoses, fittings, valves etc. All these items have to withstand the stresses generated by pressurisation and clearly they do until such time as something gives like a decrepit hose for instance.
The system design pressure is 15 psig and thus why the pressure cap starts to lift at that pressure and it will be at its fully rated relief rate if and when the pressure ever reaches 16.5 psig. The design of the expansion tank will be controlled by the axial stress in the side wall of the vessel, that or the limitations of the fused flange joint where the two halves of the vessel are mated during fabrication. The vessel will also be subjected to radial stresses but those will obviously be much lower and thus not control the design.
When the expansion vessel is pressurised the cross sectional area times the actual pressure inside it determines how much axial force the vessel has to constrain and not the relieving pressure as you appear to suggest quizically - do not confuse the two concepts. Thermoplastics typically use a design stress of 1000 psig [yield stress is probably much more than that but conservative designs for safety etc]. For a design pressure of 15 psig one would thus need a minimum wall thickness of 1.5mm - the expansion tank is probably what - 3mm thick?
The trouble is after 30 years of service and consequenty degradation of the original plastic [polypropylene maybe?] the poor thing is presumably going to need to be derated so probably notmuch fat left as it were- thus great care when pressure testing is very much the order of the day.
I will add this. I recently replaced the coolant reservoir on my 88 due to a leak. Before replacement the temp gauge would get to a needle width of the top line.
After the replacement the needle sits one width above the first line.
I will add this. I recently replaced the coolant reservoir on my 88 due to a leak. Before replacement the temp gauge would get to a needle width of the top line.
After the replacement the needle sits one width above the first line.
That doesnt make sense...Ive twice had to drive distances w/o a radiator cap, and have seen no change in temperature display..
I will add this. I recently replaced the coolant reservoir on my 88 due to a leak. Before replacement the temp gauge would get to a needle width of the top line.
After the replacement the needle sits one width above the first line.
Your ST2 will invariably tell you the real truth as to what is going on assuming both channels give the same result. The last white line represents 100C and you should be just below that at around 98C when the system is working as designed. I do not put a lot of stock in dash panel gauges but nonetheless they should be consistent.
that looks like rusty liquid, dripping from the water pump weep hole.
If so then you may have bigger issues, like head gasket time..
I would only drain and refill the coolant system with 50/50 coolant and distilled water.
NOTE flushing old coolant out could also flush out old headgasket this in turn can lead to failed headgaskets.
That said a picture of what the inside of the cooling system looks like will tell you where you need to go
I think it's the pictures, but the water is clean. The leak seems to come from the water pump pulley.
What are the root causes about a leakage by the weep hole ?
seal failure will be the likely damage but as to what caused it to fail remains to be seen. Maybe the bearing is on its way out or some debris has damaged the lip of the seal.
Once you get the water pump exposed get the system pressurised then you may be able to see exactly where the leak is coming from.
09-12-2023, 07:02 AM
