HT4100 4.1, 4.5, 4.9 Discussion, Where to install Prestone flush fitting? in Cadillac Engine Discussion; I want to install the conventional Prestone flush "T" fitting on this '90 DeVille 4.5. Obviously, it goes to the ...
I've used that little kit on about a dozen cars, and it's always the same: install the "T"-fitting between the engine and the heater, using the line that runs water TO the heater. On my DeVille, there was a question about which line is which.
And yes, I've had those Prestone fittings on cars for many years with never a problem.
I have one aswell, But when I did mine I actually took the T out and put the prestone in its place temporarily. I guess the only downside I can see is that depending on how its hooked up you could be putting to much pressure into the heatercore since their is no restrictor to bypass some of the flow.
I think the right solution is to put the Prestone "T" in the line on the passenger side of the existing "T". With a little distortion of the original hose, it can be done without an extra piece, but the best way is to have 3" of 3/4" heater hose between the two "T" fittings.