Gen2Cudas
Well-Known Member
Post subject: Slant 6 Dan and all, I would like your help- overhtng clues
Morning Guys and Gals.
Haven't been to the Forum lately as life has intruded- as it does all. Gonna go check on Red at the body shop this week. . .slow progress.
I am with a whole day to try and fix an overheating problem with Charlotte (aka "Charlie"), our slant 6 powered 'vert. I think it will turn out to be the head gasket, but I wanted second and third opinions before I tear the head off!
Background: So called Super 225, bone stock, 1 barrel (thanks Dan! The Carter works great!). We have been just driving the thing as it sat for decades without. Done the fuel mods, got the timing advanced as far as I can (44 degrees total, no detonation, runs good), just fixing what fails as you put a car back into service after so long sitting up. . .
160 stat with a oversized aluminum radiator and new pump. Has been running at one third the temp gauge for 7-8 months, winter and summer; we have made 300+ mile highway trips with no problems, lots of city driving in Dallas and Austin where she only gets to mid range idling at the lights. Overall, just quit looking at the temp gauge- problem solved.
Flash forward to about 2 months ago- driving highway at 75, been on the road for about 40 minutes, just happened to notice the darned thing was up past the midmark. Pulled over and checked the water- very slightly low but visible. Let her cool, started her up, made our stops, made it back 40 minutes north- running higher but manageable at 60-65 with the heat off the day- back down below 90, that is.
Checked everything you would check- not leaking, not "using" water out of the radiator, no water in oil, did another flush and run through the block, new lower hose that looked like it was collapsing a bit, fresh antifreeze and water, rechecked the timing and reset for advanced, etc.
Now, it starts hard and spits and coughs until it warms up, but it runs cool at idle (1/3rd of temp gauge). Sat at idle for over an hour while I fiddled with the timing and all. You drive it about 10-15 mins though and it starts to get hot- not all at once, but gradually will go to 3/4ths-7/8ths temp gauge before I run out of nerve and stop and let it cool. I smell a strong odor of ethylene glycol on occasion, but it doesn't seem to be losing any coolant out of the system. Do seem to get a bit of excess condensation out of the tailpipe on startup, but does not smell/taste sweet (I tried it). Does seem to dry out when warmed up to operating temp. When hot, I do hear steam expansion "bangs" in the system, but the water level never seems to drop enough to see. Can't smell exhaust in the water myself and no bubbles I can detect. Good flow at idle and with the throttle held down to about 3000 rpm.
Just pulled all the plugs for the second time- hoped to see some rust or something water related- but plugs still seem fine in color and wear except for one- a little discolored is all.
Just did a compression check dry and wet this morning and compared it to the numbers in my ancient Chilton manual- the highest number does not get on the chart after wet test (130 lbs) and the lowest is 115 after wet- was 100 lbs on the dry test. Note that my compression tester is NOT calibrated- just try to go with high to low differences. Not really enough difference high to low to be noteworthy- though the back three cylinders seem to be lower than the front three (118, 115, 125 versus 130, 128, 130 wet.)
My unexpert guess is a slow leak of combustion gasses into the water jacket through the head gasket- just enough of a leak to warm up the coolant beyond what the radiator can cool at speed. I'm guessing that putting this probably un-rebuilt little darling back into full temperature service finally put the head gasket OUT of service. I am hoping that since I don't find water in the oil that there is no crack in the head, piston top or cylinder wall. . .and I am hoping that not enough water enters one or more cylinders as it cools to materially rust the cylinder walls and kill my piston rings off. . .
Please, look at the above reasoning chain and tell me if I might be missing something else to look at.
Also, it would be nice to know just what a Slant 6 ought to have for normal compression pressures minimum and maximum, if anyone knows.
I've used this same compression tester on my 318 and it runs 170's to 180's. 'Course that one has more base compression. . .
Mike