I hate this, overheating, engine idling high

[lil hoodlum]

Hello everyone.

I will admit this up front I'm more of a parts changer than mechanic!

I have an issue I would like to run by those more experienced than me.

Today as I was driving my 1968 1/2 ton, the engine was idling high after a quick 5 minute drive down the interstate. 4 o'clock in the afternoon out side temp 100* plus outside. This was as I was exiting the interstate and came to a stop. Clutch peddle was depressed, 3 speed manual. I arrived at my destination and the motor would not idle down. I popped open the hood and backed out the idle stop screw. The engine was very hot. I tried to squeeze the upper radiator hose put it seems to be under a lot of pressure. I'm thinking it just might be the radiator cap needs replacing. Temperature gauge says it is at 180* but who knows. Once I got home I pulled off the radiator cap and some coolant whooshed out and the upperhose was not full of pressure. Motor still runs rough with a little back firing out the exhaust.

I have been thinking that my motor has been getting too hot lately. After driving it and with ignition off, the motor seems to be radiating alot of heat. Everything attached to the motor is also very hot.

OK stats are:

• 350 motor, non-computer controlled
  3 speed manual trans
  4 row radiator less than two years old
  has fan shround
  stock mechanical fan, no fan clutch
  reman water pump, less than two years old
  180* thermostat
  edlebrock 1406 carb with 1/4 inch heat insulator
  Auto meter electric temperature gauge
  Coolant is a nice bright green color
  No overflow tank

Tomorrow I am going to replace fuel filter (its been a long while since I replace it.) Replace waterpump, thermostat, upper and lower radiator hoses, replace radiator cap, adjust valves (also been a long time since I done that.) I also may pull the carb and check the internals to see if anything is amiss.

Am I missing anything?
Any other suggestions on something I should check?

Thank you for any input!

Keith

[67ChevyRedneck]

You popped the cap on a hot engine??? I don't know if you know this or not, but don't EVER do that!

Is this recent? As in, it's been running great until now?

The high revs could just be the carb sticking? If it's been working, it shouldn't just idle high all of a sudden, could be dirty, float stuck?

Timing could have moved too.

Lots of fun things to check.

[YBNORML]

I had the exact same problem with my blazer.
Turned out to be a stuck float on my carb.
Edelbrock 1406. Cleaned it out hasn't been an issue since.
That was last year, about 4000 miles.

[hotrod farm truck]

Could be a vacuum line fell off or cracked making engine run lean, causing faster idle and running hot.

[lil hoodlum]

67 chevyredneck, I know better about popping radiator on a hot motor, but I just couldn't help myself, I wanted to check the coolant level and see if it would relieve the pressure. I at least used a towel over the radiator cap.

This is my daily driver and I put on about 150 to 200 miles on it a week. It has been running normally except for what i perceive the motor to be too hot. Many years ago I replaced the cooling system because of a fualty gauge reading. I of course found out it was the gauge after replacing everything else. Lotsa fun!

I will definitely open up the carb and check it out. I all ready have a rebuild kit just waiting for such an occasion. Thanks.


Keith

[Palf70Step]

I would also look into an aftermarket tempo gauge. The factory ones are not know for their accuracy. Find out how hot you are really running. Also, is the pressure on your radiator cap for a closed or open system. I know there is a difference, but I can't remember which type cap is the higher pressure one.

[cdowns]

if done right theres not much wrong with taking a rad cap off while hot/// while you had the cap off did you take the temp of the fluid with a thermometer to detirmine weather the overheatin issue was real or percieved??

[lil hoodlum]

cdowns, checking the coolant temp with a thermometer is a good idea. When I get home today I will check it with a thermomter.

I'm not really sure I believe the temp gauge. It says it is right at 180*, but I believe the motor is much hotter than that. Other than what I had perceived the motor to be too hot and the guage reading 180 plus I haven't had any driveability problems until yesturday, I decided not to worry about it.

I did notice that the rubber vaccuum cap on the carb was cracked. I replaced that but have not noticed any improvement.

When I get home today I will check the coolant temp with thermometer, Change fuel filter, Check timing, and open up the carberator and rebuild. If no improvement, I will service cooling system.

Thank you everyone for your input!

Keith

[rollinhard]

Check timing and vaccume leaks as said above might be running lean or getting hot from bad timing

[68gmsee]

A "hot" running engine has certain symptoms you should be aware of.

Here's some of them:

1. Of course, the temp gauge.
2. Has a gurgling sound from the radiator.
3. Steam coming out of the cap and/or water spewing out.
4. A pinging or rattling sound when accelerating.
5. Clicking sounds that weren't there before when you turn it off.

Can't think of others right now, but the way you describe your problem seems like a normal running engine in the summer heat.

I installed a radiator cap with a temp gauge on mine to see if in fact it was running hot. I also put an overflow tank on it.

It wasn't running real hot but it would climb up to 195-200. After I put the new cap and overflow tank in, the temp stabilized and now stays at around 180-185.

[lil hoodlum]

Thank you everyone for your input!!

I rebuilt the carburetor yesturday and replaced the fuel filter. The idle is back down now and is running much smoother.

Funny note, it only took me three and half hours to do. Of course I lost pump connector rod and check ball in the grass. I searched for nearly an hour before I found the rod. The rebuild kit had another check ball, thank goodness

Before the carb rebuild, I checked the coolant temp and it was 151*. Radiator temp, inlet side, was 160 something degrees. Eldelbrock aluminum manifold was 170* So I guess ya'll were correct that the cooling system was working as it should.


Now if someone can tell me an easier way to adjust my air/fuel mixture. I use the vaccuum gauge // adjust idle method with mixed results.

Again, Thank you everyone for your help!

Keith

[QKENUF4U]

i would put my money on a vacumm leak way before anything else.. you rebuilt the carb and used a new base gasket which in turn sealed the leak......

as for adjusting ur air/fuel screws.. i turn them in till engine stumbles and then out a 1/2 turn.... have never done it with the vacumn guages myself..

[lil hoodlum]

Thanks QKENUF4U I will have to try adjusting the air/fuel mixture that way. It sure sounds alot easier.

Keith

[67ChevyRedneck]

Glad we could save you some $

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