Radiator temperture split

I'm not sure why the temperature differential would even matter . . . so long as the engine temperature is kept below the boiling point.

That's important, because when it boils, it produces steam, which actually is releasing heat energy, and steam does not have the capacity to transfer the heat of the engine that the liquid coolant does, and therefore, true overheating occurs.

And to increase the boiling point, we have pressurized radiator caps; for every one pound of pressure, the boiling point is raised two degrees.

Therefore, assuming a system with no leaks, with a typical 15lb cap, water would start to boil at 242 degrees.

The important thing is that the heat is being transferred to the coolant by the engine and it's then being transferred from the coolant by the radiator.

The fact that it was running 225 degrees in your driveway idling simply means that there was not sufficient airflow to remove the excess heat from the radiator. It doesn't mean that you need a radiator with a greater temperature differential . . . or a bigger one, for that matter.

If you want to reduce that temperature, use a lower temperature thermostat and ensure that you have sufficient airflow across the radiator; you didn't mention whether you have a fan shroud or not, so I'll assume that you don't.

If indeed you don't, that's a big (and very common) mistake if you're worried about the engine overheating parked or at speed below 35MPH.

The shroud directs all airflow through the radiator so that it can cool more effectively; without the shroud, only the area directly in front of the fan has airflow coming through it when stopped.

So . . . why don't we concentrate on how to improve airflow, and the rest will take care of itself?

I ran in some new engines this summer, and I was happy with 30°.

...make sure you don't have any holes / gaps in the core support around the edge of the radiator.

...make sure the airdam along the bottom of the core support (you know the black part that women seem to think is a curb feeler ) make sure it's not missing or all beat to crap.

...make sure the edge of the fan blades are within 1" (1/2" is better) of the dia of the fanshroud opening. (fans not too small)

...make sure the plane of the fan extends aprox 1" into the back of the fan shroud.

...when you get home (the instant you pull in and stop) get out and lay the back of your hand on the front of the radiator and feel for any cool spots. If you find any, this area of the radiator is plugged / obstructed internally and is not carrying it's load.

...most generic thermostats are a "close enough" operation. If they open within +/- 10 degrees they will probably pass inspection at the factory. Pay $6-$8 more and get a good quality, high flow one from Summit or Jegs or PAW or whoever.

...waterwetter or engine ice or any of a half dozen other products will all enable your coolant to shed the heat quicker and get a larger delta in the same time.

...also dont forget if the coolant is 225 at the radiator, thermostat housing, etc... that means inside the heads and inside the block it's probably right on the ragged edge of steam.

(imho) one of the easiest ways to help, is to give it an electric fan. Hot day, at idle, starting to get warm... nooooo problem, we just flip a switch and viola: 50mph worth of airflow.

And just because one guy gets away with a 30 drop, you may or may not be ok with that. ( maybe he runs a 170 stat and you run a 195, maybe he has a stock 289, you have a 60 over block with a stroker kit, you've got new alloy heads and his are iron 60's rejects with 40 years of scale build up in em, etc... ) too many variables to go black or white on the topic.

S-Car-Go said:

Yes, I was hoping for more than one input on the temp split. I got my truck running today (new trans) and checked it as well. It had a 25* delta. Admittedly that is a worse example since it has a cross flow radiator and is very different.

I'm gonna stand by my theroy the water in the mustang was moving too slow. Big delta in the radiator and and staying in the block too long. Then again, it wouldn't be the first time I was wrong.

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Do you have a shutoff valve in the heater hose? That'll increase movement of the coolant to the radiator.

This is a reeeeaaallll longshot, but you don't by chance have the heatercore bypassed do you?
( just looped back at the water pump)

Found that the hard way once...

S-Car-Go said:

No shut off installed in the heater hose. I do have an after market pump, so it should flow plenty to both.

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Any flow to the heater is wasted. If you don't have AC, then you can put a manual valve in the heater supply hose. If you do have AC, you need the valve anyway.