The Great Freeze Plug Fiasco
Please somebody just shoot me...
By now you should be familiar with my luck... which is all bad! After finishing up the EFI and Supercharger project, which nearly killed me and drove me into the poor house, I moved forward with trying to get the engine dyno tuned for power. The first time I put the car on the chassis dyno and attempted to do power tuning we did a pull up to about 4,600 rpm and all of a sudden there was a big cloud of white smoke and people yelling to shut the engine off. I got out of the car and saw a lake of coolant spreading out from underneath the car. Upon further inspection I discovered that a freeze plug had popped out of the block, it was the middle plug on the driver's side. So that was it for the dyno tuning that day.So we replaced the freeze plug with a new one and a few weeks later I was able to schedule another day on the dyno. The day started out ok, we did a couple pulls and got some tuning done. On about the third pull we got the engine up close to 5,000 rpm and suddenly there was more coolant on the floor. Yep, another freeze plug out. This time it was the front plug on the drivers side. So that was it for dyno tuning that day. Of course the front plugs are a real bastard to get to because they are right behind the motor mount. Nothing can be easy with this car.
We started wondering if it was the freeze plug itself that was just not right. We had been using the standard steel cup type freeze plugs, but now we decided to switch to a different type of plug. This new plug is called an expansion plug and it has a bolt in the middle that you tighten, which squashes two metal washers together to expand the plug's diameter and hold it firmly in the hole. So we installed one of these new plugs in the driver's side front hole. I took the car out for a test drive and gave it some good acceleration runs and then came back to the shop. When I got back to the shop I saw that the plug was dripping. I got pissed because I was going to have to leave the car at the shop for the evening and get a ride home, so I got in it to drive into the shop and decided to rev it up and do a smokey burnout on my way into the shop. What do you think happened? Yes, of course, the freeze plug came all the way out and all the coolant went on the floor again. This was getting old.
So I took the motor mount off again and replaced the plug with another of those expansion type plugs. About a month later I was able to get another date for the dyno. Same old story. Got the car on the dyno, did a couple pulls and, BAM, out comes a freeze plug and all the coolant spills out onto the dyno. Terrific. This time it was the front plug on the passenger side, which of course is right behind the motor mount. CRIPES! Off the dyno and onto the rack again... pull the damn motor mount and replace the plug with an expansion plug. Click thumbnail below to see the plug (the block of wood is there to support the engine because the motor mount is removed in order to get at the plug):
Notice the drain plug in the block just behind the front freeze plug. There's another just like it on the opposite side of the block. This started me thinking. I decided to pull those drain plugs and install some AN lines plumbed with pressure guages. That way I could measure the amount of pressure in the cooling passages around those freeze plugs and see if excessive pressure was causing them to pop out. Click thumbnails below for pics of the lines plumbed into the block:
I installed the lines in both sides of the block. The line on the passenger side I installed an analog pressure gauge which my friend Dennis Duke would watch while we did dyno pulls. The line on the driver's side I installed into the dyno itself which has the ability to measure and log the pressures. Click thumbs below to see the lines, my friend Dennis holding the analog guage, and the line plumbed into the dyno's instrument tree.
Results of the pressure tests:
Ok, so with the pressure lines all plumbed in and ready to go we went ahead and started the experiments. At idle the pressure in the block was only about 2 or 3 psi. As we increased the engine rpm's the pressure started to rise. By the time the rpm's were up to 2,500 we had about 15 psi in the block. By the time we got to 4,000 rpm we had about 23 psi in the block, and by the time we got to 5,000 rpm we had well over 30 psi reading on the analog guage as well as the dyno's digital pressure readout. The highest reading we saw was 34psi. Once the run was over and the rpm's dropped down so did the pressure. One funny thing was that if we shut the engine off entirely the pressure guages would drop to zero.We also had a pressure tester on the radiator during these runs and it never registered more than 7 or 8 psi at any time. Even at 5,000 rpm when we had over 30 psi of pressure in the block we only had 7 or 8 psi in the radiator. We decided to try removing the thermostat to see if that would have any effect. The only effect it had was at idle we had slightly higher pressure in the block, maybe 8 psi instead of 2 or 3 psi when the thermostat was in. The pressure still rose linearly with rpm until it was over 30 psi. Still only 7 or 8 psi in the radiator with the thermostat removed. The only other difference was that when the engine was shut off the pressure in the block would hold steady instead of going to zero.
The last thing we were going to do is go full power under load from the dyno, but we couldn't do that because unfortunately my blower belt was fraying and needed to be replaced so we decided to call it a day. We didn't blow out any freeze plugs.
So now I have to find out what is the normal pressure in the cooling passages of the block to know whether I have abnormal pressure. The saga continues...
With the thermostat removed I also decided to test it to make sure it was opening properly. I put it in a pan of water and heated it up. It worked. See pics below of the test.
