Hey Guys, the 408 in my 81 Camaro has a quirk that I'm not sure is a bad thing or just how things operate. It's got a 170* thermostat in it (according to the stamp on it, I did not install it, but I did add 2 holes to help with burping). I burped the system by letting it idle for 15-20 minutes, watching it cycle several times and the coolant level drop, while adding coolant as it's taken in until I saw no more level drops and no more bubbles. There is an overflow tank that will allow for expansion and retraction (the hose in the overflow goes to the bottom of the tank). I have the EFI temp sensor in the head, aux temp gauge sensor in the intake. The engine tends to run down the road at 180-200 degrees. Not bad for a .040 over 400 in my mind. It will creep just over 200 in heavy traffic on a hot day. It's an animal and there are no performance issues, the hoses, radiator, and intake do not get beyond what I would consider normal temps. The head temperature will hit 230, 240, even 250 degrees before the thermostat opens, but the intake temps says it's still running nice and cool at 160-170. Is this typical? Once the aux gauge with the sensor in the intake hits about 180, the stat opens. I would assume the head temps would be hotter than the intake before the thermostat opens because of the proximity to combustion and all, but is this extreme? I've never tracked head temps, so I have no basis of knowledge on their operating temps. These are early production iron 400 heads, btw. Basically the engine does not heat up fast enough for the thermostat to open to cycle coolant and keep the head temps down initially. Once the stat opens, everything is peachy and the temps on both gauges stays pretty close and where I would consider it to be acceptable. Is this normal operation? If there were still air caught, I'd think I'd see intermittent high temps regardless of the stat being open or closed, no? The only "issue" this seems to cause is the fans kicking on well before they need to, since the EFI is telling them to run based on the sensor in the head. Am I overthinking this?
Same thing happened to me with a sb 400 with brodix aluminum heads. The heads heat fast, the intake is still cool. After chasing it for a while, I realized it didn’t happen if the heater was on. That let the water circulate enough to bring the tstat up almost as fast as the heads. I added a small (6AN I think) bypass from the manifold to the suction side of the water pump. Problem gone permanently.
That's a great idea and a good catch on your part. I know there's an unused port on the intake, but I'll have to check the water pump. Were this an aluminum headed engine I'd be more concerned about those initial head temps, but do you think it's a problem with the iron heads?
No, I even chased it around with a temp gun. Just a matter of no circulation. When the stat starts to open the hot water hits, and it goes down at the head. I had the spare intake opening, and that particular water pump had a top passage plugged. I drained a couple quarts out was all to put the hose in. Bugged me, because it looked like a stuck stat.
You can play around with extra lines , Back of intake Between 3-5 & 4-6 Side of block . most time Passager side temp cooler then Driver Side with temps in head, You can have 4 temp gauges 2 in each head & get 4 different readings, With experimenting you can bounce out the temps
On one of mine was to force all coolant Threw block & heads Exit @ rear of intake , P Side #8 D Side #12 @ front a cross over #3 All back to Top Rad port , blocked off , thats where #3 line went to standalone thermostat. No thermostat at the front of the intake, A stand alone thermostat housing With #8 , 12, &3
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