There used to be a water temp sensor in a hole in the flat spot in the top of the center iron. Done away with years back, it was a perfect place to let the air out of the block. The air is now removed slowly because the front of the engine (in the car) is tipped up a bit, and the air collects near the water outlet, and is eventually pumped out of the block to be removed to the top of the radiator where it sits still until the cap cycles and lets some of it out. When the front of the engine is level with the back, or, tipped down, this is no longer possible. Air pools at the rear iron and there is not enough flow rate to move it anywhere.
At 30 degrees, you are close to not needing a water radiator to cool the engine. The engines are cold blooded, and do not start readily when carburetted. The intake looks like Santas beard until some heat is built up. We tried to race once when the temps were that low. I got mine to start with two cans of WD-40 spraying into the carb at once. Then when the WD-40 was shut off, the engine would die. We got it hot by dragging it around the paddock with the tow vehicle. The ignition was on and the fuel pumps, but it did not make enough power to run by itself. So we did a few laps with the enging half running, and it got some heat into it, and could fast idle (2,200 RPM) on its own. It had a 160 degree thermostat with a 3/16 hole through the rim to let air bubbles through. After a few light laps with 2/3 of the radiator taped over we got 120 degrees of water temp. The engine was cooling with a 3/16" water supply.
I took out that thermostat and put in a 180 degree thermostat with no holes through the rim, and that got us enough heat to race on. 150 degrees a speed.
The complex and expensive stock Mazda thermostat was designed to provide a closed loop of coolant in the block to heat the engine rapidly, and uniformly. The two reasons are: Poor combustion in the large and cold combustion chambers, thus high HC output, and the block is heated on only on the plugs side. Inlet air and fuel on the exhaust side overcool that side. So it is the job of the coolant to keep the exhaust side of the engine close to the temperature of the plug side so the engine remains about the same length on both sides. So, there are more case bolts on the hot side than on the cold side. You may discover that when overheated massively, the rotor housings on the hot side will be shorter after the engine cools, and begin leaking water. There is also a need to have more clamping around the combustion chamber to prevent scrubbing the housings on the irons. Very high output engines use an additional dowl around each case bolt to prevent such movement.
A fixed rate of heating to an overheat suggests too small a radiator. A rather sudden overheat suggests trapped air in the system. If radiator size is marginal, a reduction in power will reduce coolant temps. If the system has air in it, the temperature will remain high or go still higher.
For oil cooling, the power setting has a closer connection to the temperature. So on a scalding hot day shifting at 9,400 RPM rather than 9,600 RPM will bring the oil temps right down. I look for 180 water and 160 oil, but 200 water and 200 oil won't hurt anything.
Lynn E. Hanover
Hi Neil,
Yes, I recall that you and Jim did use a thermostat plugs up with no problem. I found burping the block (actually my cores) necessary even without a thermostat. It could be that I did it the same number of times I did without the thermostat and that was insufficient.
I normally would run the engine 5000 rpm for 30-40 seconds to burp the air. Would need to do this about 3 times before I got all the air out of my cores. Because of my ignorance of all factors early on when designing the plumbing for the cores, I had both inlet and outlet on the bottom – not conducive to getting air out of the cores.
So should have one tube going in the bottom and the other out the top or both out the top or at least a spigot on top to release the air as the tanks filled.
You know – the old "should have, could have, would have - but didn't". Now it's just simpler to burp the engine three times on the infrequent occasions I drain the coolant.
|