My Slant seems a little ill

[dartman59]

1971 Dart /6. About 85000 miles. Three sp manual transmission. I am having a hard time diagnosing what seems to be a sick or injured engine. It all started about 3-4 weeks ago. This car is my daily driver this time of year. It has always run nice and cool, no matter what the weather or the load. Never had an overheating problem; in fact, in the wintertime I complain my heater doesn't blow hot enough air (new core, so no problem there...).

Recently, on a 15 mile ride, I noticed after about 5 miles that my [ame="http://www.amazon.com/s/keywords=temperature%20sensor&index=garden"]temperature gauge[/ame] was up around 1/3-1/2. Not quite to the half-way mark (non-rally, stock dash & gauge). After about 10 miles (cruising at 65-70 on the interstate), I started smelling coolant. After 15 miles and when I pulled into my driveway, I had pretty much lost all my coolant through the puke bucket, which doesn't have a cap on it. Coolant all over the engine compartment. Big mess.

This car has NEVER overheated before. Why this all of a sudden? So, I filled up the radiator (with plain water), fired her up and let it sit until the thermostat had opening and I could see that things were flowing, put the radiator cap on, and took her for a spin. Everything was fine, temperature gauge at the 1/8-1/4 mark as per usual, and after about 5 miles the gauge crept up to 1/3-1/2 mark, and I headed back to the house, where I found that I had again lost my coolant through the puke bucket. When I stopped the car I could hear a humming noise (engine still running) and when I popped my hood the puke bucket was boiling over and the radiator cap was doing the humming and vibrating, as coolant was boiling out of the radiator and into the puke can.

The important thing here, to me, is this overheating was a sudden occurrence. Never happened before, so why now? Since then I have done the following:
- New water pump.
- Flushed the cooling system extensively.
- New thermostat.
- New radiator cap.

Guess what? Still is overheating, and not running particularly well. I noticed at one point that the vacuum hose on my Holley 1920 carb that controls the air cleaner flapper had come off the fitting, and that fitting was just sucking air all the time. I thought, "Ah ha! I'm running lean! That's my problem!" So, I fixed that, but it made no difference. In fact, the engine runs like crap when I close off that vacuum port. The rpms drop significantly and I have to boost the throttle to keep it running.

Which makes me wonder if I have a valve-related problem? Could my valve timing be off? Would that cause symptoms of overheating that came on suddenly?

I know this is a long rambling post, but I'm confused and a little bummed out about this. I feel like there is something going on with this engine that I cannot understand, and I don't like that feeling.

Any ideas are appreciated!!

Thanks!

 

[BillGrissom]

A number of things can cause over-heating. At least on your car, boil-over usually causes no lasting damage, unlike most 82+ engines w/ aluminum heads that easily warp. First suspicion would be a water leak. My sister's 65 Mustang 6 cyl kept boiling over every 50 miles on a drive from FL to VA long ago. She stopped at one shop that said "must be the head gasket". I was only 16 then but knew enough to talk her out of that big expense and delay. Re-filled water, drove on and stopped at a busy shop that fixed it in 5 min for $5 - a pin-hole leak in a heater hose that you didn't see until pressure built up, and such a fine stream it didn't leave visible water.

If you had a bad head gasket, you would see foamy brown oil mousse in the radiator, like I did in my 82 Aries. Even with that, I could drive 25 miles home before it boiled over, which I did for a month before junking it.

If none of above, suspect lean idle. I had that for decades in my 69 Dart w/ Holley 1920, though it rarely boiled over. My 4th carb fixed that. My 65 Newport would also boil over, especially when my Holley Pro-jection EFI box got hot and made it idle really poor.

 

[TrailBeast]

Not all head gasket leaks intermix fluids Bill, you know that me thinks.
Some leak compression into oil, and some into the waterjacket, and some can miss both and come right out the side of the head. (Rare but happens)

That's a good call on the small leak, and a cooling system pressure test will help with that. (pump it up and look it over good)
85,000 ? Could be a head gasket. A pressure test with it running can find that by pumping the system up to pressure (say 12 lbs), note the pressure carefully and rev it up good a few times.
Is the pressure higher?

His prime symtom is overheating from coolant loss, be it coolant loss then overheat, or overheat and then coolant loss.
They are hard to tell sometimes, but the pressure testing can tell you which one it is.

Start with the easy obvious stuff first though for sure. (The possibility of a small leak)

 

[TylerW]

You almost certainly have a blown head gasket. The factory cap is rated for 16lbs so there has to be some serious pressurization of the cooling system to force it into the overflow.

You can test the coolant for combustion gases but I'd go ahead and pull the head to look inside anyway. If it has a steel shim head gasket they can simply rust away and fail without being overheated. Good luck.

 

[BillGrissom]

You almost certainly have a blown head gasket. The factory cap is rated for 16lbs so there has to be some serious pressurization of the cooling system to force it into the overflow.

You can test the coolant for combustion gases but I'd go ahead and pull the head to look inside anyway. If it has a steel shim head gasket they can simply rust away and fail without being overheated. Good luck.

I have filled many an overflow bottle from just low coolant and over-heating. Steam alone can produce a lot of pressure, that got trains to CA. I would certainly do the gas test first. I still have a kit from CA Customs or such w/ test fluid that is supposed to turn yellow if you suck combustion gases from the radiator top. It never indicated anything on any car I tested. Usually a head gasket leak will put messy oil into the coolant, and I mean a thick brown mousse like the La Brea tar pits, not just a thin oil film.

 

[memike]

I remember seeing my brothers 340 blowing pressure out the dip stick tube
Yep a blown head gasket