Odd 368 situation


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By mjs - 4 Months Ago
So ever since I've had the engine rebuilt it's had temp issue.  It runs fine just that after a short while the temp gauge will max out.  I have checked it with an IR thermometer and all of the readings read okay.  Usually around 170 on the rad, 190 on the t-stat housing, 190'ish at the sending unit.  It doesn't matter whether it's on the road or sitting still.  It shouldn't be the IVR since the fuel gauge works fine.

So today I decided to first try replacing the sending unit.  When I removed it I did have some coolant pour out and onto the valley pan.  I installed the sender and wiped up as much of the coolant as I could and then started the engine.  After it had been running for a while, about fifteen minutes, I heard a bang.  The oil cap had blown off the draft tube, the filter in the breather cap had blown out, the dip stick was partially out, and the valve cover gasket on the left head had blown out.  It was, of course, steaming.  Before this had happened I had been measuring the temp and it was only at about 125.  

Has anybody ever seen this happen before?  I assume that it's from the coolant that was spilled even though it was a small amount?

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By miker - 4 Months Ago
Spilled coolant wouldn’t play into this, but the only time I’ve seen something like the caps blowing off was gas contamination in the crankcase, which finally ignited. Was it steaming at 125 degrees, or smoking out of the open gasket, cap etc.?
By charliemccraney - 4 Months Ago
It shouldn't be from the coolant.  If the engine is sealed properly, it only got on it, not in it.  Also assuming that the crankcase ventilation is working properly, any steam from coolant contaminating the oil would not build up pressure to allow an explosive release.

I also think gs got into the crankcase and ignited.
By Ted - 4 Months Ago
mjs (7/5/2019)
So today I decided to first try replacing the sending unit.  When I removed it I did have some coolant pour out and onto the valley pan.  I installed the sender and wiped up as much of the coolant as I could and then started the engine.  After it had been running for a while, about fifteen minutes, I heard a bang.  The oil cap had blown off the draft tube, the filter in the breather cap had blown out, the dip stick was partially out, and the valve cover gasket on the left head had blown out.  It was, of course, steaming.  Before this had happened I had been measuring the temp and it was only at about 125.  

Has anybody ever seen this happen before?  I assume that it's from the coolant that was spilled even though it was a small amount?

If the engine is running on the rich side, then fuel vapors will make their way to the crankcase.  On worn engines, these vapors can get ignited and have a flash explosion that does as you describe.  Not common but does happen.
By mjs - 4 Months Ago
Thanks for the responses.  
The last time I had driven the car, several weeks ago, it was running rough.  It would idle just fine just had problems on acceleration.  I discovered that the distributor was loose and had rotated quite a ways.  Not just a couple of degrees but about 20 or so.  I've never had any issues before so I assume this could have caused problem.  Before I reset the timing there was some smoke coming from the oil and breather caps.  

 


By RB - 4 Months Ago
I would say 90% chance it was fuel that got into the oil , vaporized and had some kind of ignition source.. I have seen this happen a couple times. Once a guy I know had a fresh 427 Scrub in a 67 Vette.. Top flight fresh restoration.. They were having trouble getting it fired for the first time. It was slated for the Barrett Jackson auction and they were scrambling to finish the car on the show grounds.  After cranking on the distributor and pouring fuel it it, It lit off  . Blew both valve covers clean off the engine. That stopped everything in it's tracks.. Fortunately the flying covers did not contact the body  and after recovering from the shock and then scrambling to find new covers, the car made it across the block.  I was friends with the owner but inside I had a perverse satisfaction from seeing a BBC literally blow it's top. Of course I never brought it up ever again to the owner....  LOL
By KULTULZ - 4 Months Ago
If the crankcase was smoking, it may indicate the crankcase ventilation system is not working as designed. Engineering changed the road draft system on the 55/56 model 368CI run and having an open and clean filter fill cap is important as there is no other place to vent excessive crankcase pressures.

Most likely, the engine was running rich, the engine oil/crankcase got overloaded with gasoline fumes and the mis-adjusted IGN timing set it off.

Pull the dipstick and give it a sniff test, If it smells of gasoline heavily, there is your problem.
As for the cooling system. if the infrared thermometer shows no excessive coolant temp, then the problem(s) is in the gauge circuit.
By wrcannon1 - 4 Months Ago
I race a car with a 368 and had a problem with blowing head gaskets between the cylinder and a water passage. The result was to pressurize the cooling system beyond the cap limits pushing water out and then overheating. I finally determined the cause by putting a pressure gauge in the cooling system.
If you keep having problems try testing the water pressure.