ADQ - Another Dumb Question

jwinkler · #1 (**permalink**) 08-22-2003, 06:34 PM

I had the car out last weekend (after draining and filling the cooling system). All seemed well until close to home the temp started creeping upward. It was a cooler part of the day, and until then the car had held steady at ~190 prior to that.

I was hoping it might have something to do with the system not being full, so today I was going to top it off and discovered I hadn't secured the radiator cap - it was on enough to get past the safety(?) detent, but I had not tightened it all the way.

The ADQ - if the cap isn't keeping pressure in the system, could that lead to the overheating?

Thanks,

JLW

mrmustang · #2 (**permalink**) 08-22-2003, 06:43 PM

If the system is not under pressure, yes, it could run hotter than normal. Also, if your not using a combination of water and ???? (Motor max, Water wetter, etc), and you have air bubbles in your cvooling system, then this too will cause a hotter than normal running condition........

Bill S.

Excaliber · #3 (**permalink**) 08-22-2003, 06:57 PM

Bill
I thought the REASON for over heating due to no or low pressure in the cooling system was the "boiling point" factor. IF the water boils at 212 (which it WILL with NO pressure) water will be pushed out of the system. THEN you will be LOW on water, as a result, over heating or higher than normal temp.

The OTHER possibility is that the "lower" water temp (ONLY 212 or lower) does allow as much "heat transfer" as a higher water temp would allow for?

Water temp at 240 Deg F sheds more "BTUS" than water temp at 211 Deg F. Not sure my idea of the thermodynamics postulated here "holds water"........

Ernie

mrmustang · #4 (**permalink**) 08-22-2003, 07:05 PM

Hey Ernie,

Yes, you are correct that the boiling point will indeed be lower, but at the same time, could you imagine the air being sucked in to and circulated through his cooling system by not having the system closed and pressurized. At the same time, the overall thermodynamics of the coolant (no matter what the coolant is) will be effected by the inherent hot spots located within the engine itself. Trapped air within the system will cause the same results as what JLW posted above. Sometimes overlooking the simple things, and over analyzing the current results will cause more of a headache than there needs to be.

Bill S.

jwinkler · #5 (**permalink**) 08-29-2003, 03:55 PM

Thanks for the replies - a test drive last week in the middle of a Texas day saw the temp gauge hit 210 sitting at a light due to the road heat/engine heat combination overwhelming the fan's capabilities (I need to get the right CR Spal set-up from the CRII team!), but then came right back down once underway.

Thanks,

JLW

Janusz · #6 (**permalink**) 08-29-2003, 08:26 PM

I have a new aluminum radiator, with the thermostat being in the line from the engine to the top inlet of the radiator (no expansion tank). The top inlet is approximately 1" below the top of the radiator, which is mounted at a slight angle. I have no fill point or vent in the top of the radiator and have been considering pulling the radiator and having a threaded bung welded at the highest point, to let out the air when filling the system. So is there a better/easier way to get the air out?

John

Excaliber · #7 (**permalink**) 08-29-2003, 08:32 PM

There are several other cars out there with that type of problem. Jaguar XJS comes to mind. No EASY solution (short of welding something in)!

The trick on an XJS was straight forward. Fill it, drive it, fill it, drive it some more, park it with the nose down, fill it again, stand on one foot, repeat! If you FAILED to get all the air out doing this it WOULD over heat and that gets costly quickly!

Ernie

Janusz · #8 (**permalink**) 08-29-2003, 09:08 PM

Ernie,

So would that be the left or right foot?

What's interesting is that I rarely go over 170 degrees, even in traffic. About a quart of coolant gets pushed through the radiator cap overflow soon after the engine warms up (due to the air expanding?), then gets pulled back into the system when the engine cools. Anyone else with any other thoughts?

John

Excaliber · #9 (**permalink**) 08-29-2003, 09:22 PM

Seriously, your right, a couple of "heat cycles" generally does work to get the air out, just someting you need to keep an eye on after any kind of major water lose.

The XJS was perhaps the worst I ever worked on. Just a royal pain to get the air out and SO sensitive to over heating if you didn't get it right! They were about the only car I know off where you HAD to have a thermostat in the engine. It would CERTAINLY over heat without the TWIN T-Stat's in place!

Ernie