View Full Version : Running tad bit cool - thermostat or ect sensor?

07-26-10, 05:06 PM
Yeah - that's a switch, eh? A Northstar running cool!

My '97 ETC coolant temp has always been really steady at 196 or 197 degrees when cruising, on the highway, once warmed up. Winter - Summer, no matter - always 196 or 197. Lately, it's been lower - 188 or 190 when cruising. Temp gauge needle position has also shifted - now it sits just a hair to the LEFT of 12:00. It still warms up quickly, and here in Phoenix where it's 110+ during the day, the coolant temp will go to 220 or more in stop and go traffic. Anyone else ever experience this? Think I should change the thermostat...or the ECT sensor? I've had thermostat's stick open and stick closed, but do they ever just get a little lazy? I'm kind of inclined to just leave it alone right now - it's still running plenty high to get into closed loop - what do you guys think?

07-26-10, 06:16 PM
Don't fool with it. It goes loop at about 160, so that's fine, as you said.

Entirely possible that there's a small chip of engine overhaul something wedged in the thermostat spring or disc, causing it to bypass too much radiator coolant to the engine system: the heater circuit temperature is the main control for coolant circulation changes.

As a reference base, there is a very definite "right and wrong" way to install a Northstar thermostat - look closely at the second diagram: this is exactly backwards water flow from a normal pump-in-front V-8 thermostat outlet install.....................

If JimD sees this he'll know whether the ECT resistance is high or low when cold...........that drives the gauge/temp display.

07-26-10, 07:23 PM
Thanks Sub - is it even possible to install the thermostat backwards?...can't remember right now, but I would have thought no. Anyway, I'll live with it as-is. I might have to do something eventually...maybe later in the year, around the Holidays, when the temps in Phoenix drop to a bone chilling 40 degrees. Brrrrr.....

Oh - please explain this:

the heater circuit temperature is the main control for coolant circulation changes.

Also, who was it that recently told someone that the EGR passages are in the coolant crossover just because it was a convenient place? Was that you?

07-26-10, 09:08 PM
EGR (on some models) uses a casting mount on the firewall side of the coolant crossover - easier than pouring a cylinder head with a dedicated lump and necessary machining on the driver's end of the head. An electrical stepper valve and insulated piping and away we go.........

Until the entire engine and heater circuit comes up to 188 degrees+ the thermostat does not move - at that point the thermostat begins to creep open and the cold radiator coolant is bled into the engine circuit. As the entire cooling system warms, the thermostat opens further, and the engine load (heat transfer) determines the amount of cooled radiator coolant bled into the system in order to maintain temperature equilibrium in the system: You coast, the engine cools, the thermostat closes somewhat and average temperature is kept the same by not allowing cool radiator coolant into the system. You get crazy, punch it, increase heat load, and the thermostat eases open, allowing cool radiator coolant into the loop, maintaining temperature within design limits. On the highway, steady load and speed, the whole system happily swishes around and coolant flows through the heater circuit and the radiator circuit at the mix rate necessary to maintain design engine coolant temperatures.

The expanding wax pellet thermostat is elegant - and has faithfully worked for over 80 years. 70 years ago cars with heaters actually used hand operated bypass valves to control engine and cabin heat !!! Does anyone remember the pure alcohol antifreeze ratios ??? A Ford temperature gauge sticking up out of the radiator cap on top of a beautiful chrome radiator shell ??

07-26-10, 09:42 PM
Yeah - that's a switch, eh? A Northstar running cool!
yup, that's a first.

is it even possible to install the thermostat backwards?
I seem to recall that it is, but can't swear to it.

Does anyone remember the pure alcohol antifreeze ratios ??? A Ford temperature gauge sticking up out of the radiator cap on top of a beautiful chrome radiator shell ??
You got me there Sub.

07-26-10, 09:51 PM

07-26-10, 10:04 PM
I remember as a kid in the early 60s seeing cars that had overheated and boiled over in the spring, and my father said it was because they were cheap or ignorant and had used alcohol as antifreeze during the winter instead of Glycol (Prestone/Zerex) type. Not sure if that was true, but I do rememebr him saying that. I guess the alcohol water mix was OK in the winter, but had too low of a boiling point for warmer weather.

I got you now about the heater circuit - you're saying that the temperature "signal" for the thermostat is part of the heater or block circuit - different from the standard design - I see your point, and it's a good one.

I remember reading that the EGR circuits and passageways were specifically and deliberately placed on the coolant crossover to provide for extra large passageways and also for cooling of the exhaust gases to take place, to prevent any possibility of clogged passages, for all intents and purposes. Pretty sure I read that in the '97 FSM - could double check it if you like. I'm not trying to say you're wrong just to say it - just want to let you know that the EGR location was a well designed and thought out plan to avoid EGR passageway clogging - an example of creative engineering that none of us ever really appreciates or considers. Sure, the EGR valve might be known to clog sometimes, but I never have read of clogged passages, and I'm pretty sure that's not uncommon on some earlier design Cad (and other mfr.) engines.

07-26-10, 10:13 PM
Just remember the 4.9 EGR tubes down in the TB. Common clog point. Never happens on the Northstar. The only choke point is the EGR pintle valve.

07-27-10, 08:56 AM
Curious about the EGR cooling idea.......might be a part of the Northstar design. The EGRs on some of the Olds 455s I build just dump directly into the side of the intake manifold - of course they don't exist when I'm finished - marine engines don't have EGR and Edelbrock Performer manifolds have no provision for it.

I know that my 2002 STS has the EGR sort of hung out in the breeze on the rear side of the crossover and the gas passages are in the crossover and heads, so there has to be some cooling taking place there.