Ho everyone,
I’ve recently installed a 383 new engine, mild cam into my c4 91 tpi and yesterday decided to do a few tests using the blue fluid that detects CO2 and the liquid changes color to greensih at cold start. There are bubbles coming from the top tank as well. I felt it was running a little rougher than before that’s why I thought maybe something was not right.
Back when I fired up the engine after it was installed, there were some potentially damaging episodes. The ECM fan relays failed and the fans didn’t start but I saw the temperature on the datalogger display and shut it down at 230F. it continued to rise up to 237F. However, I don’t that was that high. The engine was installed in a shop and they started it before I came a few times, normally it needed the 2000-2500rpm initial constant run but it’s a hydraulic roller cam so maybe that’s not that critical. Another weird thing was while trying to do that 10 min initial neutral run the exhaust manifolds started to glow red, it was dusk outside so it was more easier to noticed. this lasted for like 10s . I saw white smoke inside and the mechanic saw it and told me to stop. I suspect this is when it warped a little. Maybe it retorquing the heads would’ve helped. Later upon that, I don’t remember exactly, the car would overheat at idle with both fans on. slightly faster than the previous engine that also had a head gasket failure. Later I’ve replaced the radiator and the secondary fan was able to keep it at target temperature of 185F while idling, and same temperature on the race track. The old radiator had a lot of sand grains in between the fins but probably with a normal engine it could’ve be capable of keeping handling idle conditions. The new radiator is double row aluminum and probably much more efficient and able to cope with a small head leak.
Another issue was the AIR system was not installed correctly and the exhaust would pull air through the check valves over the O2 sensor which caused very rough idle and rich mixture. This made the oil look black quickly. It is possible too much gasoline sprayed washed the oil from the cylinder walls or other related problems.
until now I drove it about 800miles plus 30laps on a race track.
the intake is ported base edelbrock high flow with runners, and 1205gasket; two 100cpsi Cats front.
I have afr on right bank and I’ve been monitoring it to keep it safe while tuning the parameters
there is also an exhaust gas temperature sensor installed that I’ve been monitoring. this reads from 850- 1100f at idle and up to 1400f on the race track.
the head gasket is a felpro 1003

now I’m planning for opening the heads and see what’s in there. Any idea what was the cause? thanks.

 

That is a good gasket, make sure the block and heads are flat. To me it does not seem like you did anything that would have caused the failure.

 

I think something happened when those manifolds went glowing red, on both sides, which meant very high exhaust temperatures. At that time I had the EGT ready but hadn't installed it yet.
yes, we will check the block and inspect the heads, cylinders, pistons maybe pulling the oil pan would be a good idea. The heads at least would probably be be warped

 

The glowing manifolds does not really mean much, it could have been retarded timing and running at high RPM. When the timing is retarded the mixture is still burning when the exhaust valve opens and it puts heat into the exhaust system causing it to glow. That heat is not going into the combustion chamber causing a head gasket failure.

 

I understand but theoretically the heat in the manifolds if they are very hot, could go to the cylinder heads and heat them up unevenly. Thin headers have less mass and would transfer less heat.
It could be that the mechanics at the shop did something wrong before I came. I remember they said they started the engine for short periods of time and when I came both ECM fan mosfets were fried and I shut it down at 230F but they had no way of monitoring the Coolant temperature because where I arrived the coolant gauge wire wasn't hooked up. I had to turn fans on manually using the two toggle switches that were fitted a few years back. The PSI sender was also not reading anything and I asked them to bring an external gauge. I've also noticed they were kind of sad ). Maybe because it's a wasn't that easy to work on it. So Ecm mosfets failure... maybe caught them by surprise. But anyway I can't say for sure.

 

Not sure why they would start a new motor with no temperature gauge or oil pressure gauge. That’s pretty important. I wouldn’t necessary worry about the glowing headers. My motors have always had glowing headers after high idle for a minute or so. Don’t know why and don’t really care. Haven’t lost a motor yet and runs mid tens all day.

 

they said they started it up only for a very short time.
What was weird is when I left the car in their shop the gas tank was half full but when I got there after they started it up the fuel gauge was on reserve. I was also burning more fuel because of air pulled in over the O2 sensor, but normally I was expecting to see a lot more in the tank. Another thing that I remember is we were topping up coolant and although the coolant was not hot yet, it suddenly spit out like 1m high. At that point I wonder if the combustion was already leaking into the coolant, this was before the glowing manifolds, or it’s when the thermostat opens up?

 

:I did some tests today on some of the cylinders.
Compression: 3:180;5:175; 7:172; // 8:180; 6:170
leakdown tests: the indication on the second gauge was on green but I could hear some noise of air flow coming from the exhaust manifolds at no 5, 6 and 7. I want to check the tester, or maybe replace the second gauge that doesn't read in PSI.
while the no 6 was connected to air, I saw some tiny bubbles in the coolant top coolant tank, like clusters of 20 and 0.5mm in size
I also have a screenshot from my oscilloscope that was connected to a DIY piezoelectric pressure gauge.


From this picture those pulses may mean one of the cylinders could leak into coolant from one of the cylinders. The larger period between them may be an indication of a missfire. I'll try to disconnect one injector at at time and see what happens.

PS
I’ve repeated the test, this time I held the sensor steady in my hand, previously I had given it to a friend, it’s possible he didn’t hold it properly. The sensor is very sensitive on pressure changes. It reacts to less than 0.5psi. There are no detectable pulses in the coolant when cold. The only thing that happens is if I put a hose from the top tank into a water bottle after like 30s there are a few bubbles coming out then nothing. If there is a leak it is very small and it gets sealed after the engine warms up.