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Originally posted by quicker6
I was gonna try that stuff but, Im not so sure which local vendor here carries RMI25. Im gonna flush out my coolant when I change out my t-stat. Anyone ever had a thermostat that got partially stuck open (not fully) that ended up backing the coolant flow into the reservoir some?? My car seems to have that problem and Im pretty sure its the t-stat
Derek
Why would a partially stuck open t'stat cause coolant flow into the overflow?

Partial or full open, system pressure would be the same. My guess is one of 2 options, bad rad cap or head gasket. Remember, when hot, the expanding water is forced into the reservoir, and then pulled back into the rad when cooling.
Would just like to add comments about some of the other posts here. As we have much more severe heat loads on our vehicles here in the desert, we see and experience the extremes in engine cooling. From May to October 100 deg. days are common place, with weeks of 110+ during the "hot" season.
For cars that do not visit the freezing temps up north, they do not use antifreeze as it does not cool as well as plain water. For over 10 years, cars that have used RMI with the water, and flush periodically, have cooling systems that stay clean and troublefree.
For the few that need to use antifeeze, it also is treated with RMI changed every season.
If just antifreeze is used, the extreme temps here destroy the additive package it contains before the end of summer, and starts to leave deposits in the system. Have seen very low mileage cars that were stored for years, yet with only antifreeze, the system is very corroded from just sitting. Flushing the cooling system every year is a good routine.
Just because the fluid "looks" fine, does not mean its chemical balance is proper. The comment about sacrifical annode attests to that. The fluid is circulating in a system with dis-similar metals. This is the basic theory behind a battery; hence, you have galvanic corrosion.
There are 2 functions that RMI-25 provides that no other single radiator additive that I have found over the years can do. One is it contains properties to inhibit corrosion and provide the proper PH balance. The other is it cleans the system without a caustic or acidic solution that would be detrimental. [It also contains a surficant like WW to aid in heat transfer for better cooling.]
One final note, a performance car or race car using antifreeze at a drag strip is not only against track rules, but just plain stupid for 2 reasons. If you blow a hose and it gets on your tires, an abrubt visit to the wall can ruin your day. It is also VERY difficult to clean from the track surface.
A blown head gasket can also ruin your day as well as your bearings if the coolant reaches them. A very small amount of antifreeze will immediately trash a bearing. We have had cars driven 30 miles or so with water/RMI in the oil and been able to flush the engine and do the repairs w/o replacing bearings.