I’ve been experimenting with two temperature gauges (one mechanical, one electric) in my early 1970s blown 6-71 Chevy 454. Both sensors are hooked up opposite each other at the rear p***enger and driver side ports at the back of the intake. A few times now I’ve noticed that when opening these ports up to swap sensors around (while the engine is fully cold, a full day after the engine has run at full temperature) there is a lot of air beneath these ports. The moment I loosen the sensor nut, I hear gurgling; slowly fluid will rise, eventually spilling over. If I open the (16lb) radiator cap, the fluid will of course rise and overflow much faster. This phenomenon occurs on both ports/sides of the engine. Is this cold-engine air pocket normal? I would think not. I have no way of knowing if the air exists under normal operating temperatures/RPMs. I've never seen oil and coolant mixing in this engine, so I don't think I have a bad head gasket or cracked jacket. Also, interestingly, no matter what port I plug in the mechanical gauge it always reads far lower than the electric gauge. I’ve tested both sending units in boiling water – both work well and are calibrated correctly. No kinks in the capillary tube, and the connections on the electric check out. But the mechanical always reads around 40--50 degrees lower than the electric once both are in the car. Laser temperature reads don't show this differential around the ports or anywhere else. Despite being a low compression engine with an under driven blower (I've never gotten into the boost) the engine tends to run a touch on the hot side -- sometimes dipping near 210 in slow traffic -- but has never boiled over.
you're just looking for problems, eh? how about if you install the gauges where they're supposed to go? either the thermostat housing, or the head between exhaust ports, if they have the 1/2" npt hole there (most do). get back with us
The air thing is interesting. One would think those smart factory engineers designed the water jackets in such a way as to drive all air up and out. Not sure how this is happening.
Coolant expands when it gets hot. It shrinks when it gets cool. What you are probably seeing is the void left after it cools and shrinks.
That is not an unusual situation. On most of my boat 454s we put a small elbow and run a crossover line to allow them to vent from side to side. Some people put pet****s in the rear intake ports to bleed off the air. Unwanted air in the coolant p***ages can occasionally create undesirable problems.
What are you using for a recovery or BURP TANK, or whatever the hell its called? Proper radiator cap is needed as well. It should **** anti freeze from the tank back in the radiator like little kid ****ing his snot back in the pie hole.
I see a fair amount of rear cross over systems on race cars with both sbc and bbc Chevys. They tell me it is needed because of the trapped air. Causing uneven cylinder heat. I would think Chevrolet would have done something about that if it was a problem.
I have 4 temps on SBC , all gauges calibrated and noted, 2 mec & 2 Elt, The driver side Like every 15-20 mints will go from steady 190ish to 230 ish little over for about 5-8 sec then drop down to 190, I have looked in heads & pulled freeze plugs, Run cross over , plumed lines from back to front , Vac fill cooling system , still does it ,, Only thing I have not done Yet is to Plum lines between 3-5 & 2-4 SB2 block cure this problem over Gen 1 sbc
I'm seeing the same thing on my 454 (mid 1970s). The peaks and valleys may be coinciding with opening and closing with the t-stat -- the mechanical temp sensor up there reads normal. I'm pretty sure this is a series flow (coolant) engine/heads, some suggest that is a cooling drawback on these older big blocks. So maybe this is a byproduct of that design. I'm also reading that temp sensors on the heads tend to indicate hotter than the rest of the engine. I'm certainly seeing that. And... I just had an old freeze plug start dripping -- and damned if it wasn't one behind the flywheel! So I've got things taken apart at the moment. Interesting little corner of the universe inside that back side of the engine...
@John Starr Follow up on mine More experimentIng , Tried many different routing . As of Now, I am forcing all coolant Threw font of block & heads Exit @ rear of intake , P-Side I have a # 8 Back to a remote Thermostat housing D-Side has a # 12 to remote T -housing . Capped off Front thermostat location No thermostat front of intake , A #3 line to remote T-housing , All 3 lines to Remote , then coolant threw remote then to top of Rad 1-1/2 main house .
As the results and articles above show, it’s common in V8’s. Might be why Ford had this “experimental” cooling for yblocks. Shown on Duane Spencer’s 55 bird. Supposedly designed for the NASCAR engines. The Rolls Royce Merlin liquid cooled V12’s had a variety of design temperatures, but normally at least 248*F. No big secret that it makes engines more efficient.
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