Engine runs hot at idle and low speeds

[retro dreamer]

Gentlemen,

My 1975 Chevy 350 small block seems to run hot all the way up to 210*when at low speeds and idle. it seems to stay around there if i keep the heat on but I'm afraid then engine might get damaged.

I've recently changed the oil and oil filter. The thermostat is 180* and is around a year old. I had no such trouble last summer, what could it be?

How do you know when your water pump is shot.

Thanks for helpin a newby tryin o teach himself the ropes,
Perry

[vectorit]

Are you runnin a clutch fan?

[67ChevyRedneck]

The front of it will wobble and/or it pees water out of a hole in the front of it.

[Jacfourteen]

usually a low speed problem has to do with insuficient cooling in the ratiator. This could be from a clogged radiator or from a fan problem. Do you have a clutch fan? If so I would check out the clutch, when the engine is hot you should hear the fan moving air when you rev the engine. Other things that might be wrong is no shroud or incorect fan. Hope this gives you some ideas.

[attack eagle]

overheating at idle or low speed stop n go USUALLY indicates insufficient flow of air over the radiator, or some radiator passages are are clogged or too small a radiator (particularly when it works fine on the freeway).

it can (unlikely) be a symptom of a water pump impeller that is corroded away or clogged with mineral build up, which reduces flow... generally though in that situation you will have problems at speed as well.

[D.PASSMORE]

Make sure you have the correct thermostat in the waterneck. I was running a 160 deg, same problem. Check the manual and installed a 180 deg. Solved the problem.

[69GMCLonghorn]

In my experience, the guys above are mostly on the right track, except D.Passmore (you've already stated you have a 180° T-stat). One thing that has NOT been mentioned is the flow through the engine block itself. I had this problem on a Chevelle years ago. I had to radiator cleaned/rotted out, but the biggest part of the problem was that the block needed to be back flushed. This is something a good radiator shop can do for less than $100. They do just what it implies: they BLAST water backwards through the block and remove any build up, etc. Do yourself a favor and look into this. If it isn't a failing water pump, I'll bet this helps your problem.

KEEP US POSTED! We'd love to know what the problem and solution is!

[retro dreamer]

HEy Thanks a lot Fellas.

I'm gunna get on it toniht and report any success.
One thing though, May seem like a stupid question but, How do I know if I have a clutch fan. I have never seen the fan not spinning, does that mean anything?

thank you kindly,
Perry

[69GMCLonghorn]

Originally Posted by retro dreamer

HEy Thanks a lot Fellas.

I'm gunna get on it toniht and report any success.
One thing though, May seem like a stupid question but, How do I know if I have a clutch fan. I have never seen the fan not spinning, does that mean anything?

thank you kindly,
Perry

WITH THE ENGINE OFF, reach in and try to turn the fan. If it turns, then you have a fan clutch. If it will only turn if the pump turns, then you don't. This really should have no bearing on low speed/idle overheating problems. Clutch fans lock up under about 1200 RPM (yes I know, this can vary).

[woodman13]

Common problem IMO could be the following:

Air in cooling system
bad Water pump (can be bad and not leak or wobble just lack of antifreeze over time will eat the impeller off the shaft and decrease water flow.
Lack of correct/missing shroud or fan.
Lack of antifreeze (I use water wetter for 10 degree average drop in temp).


Need more info on your system to come up with a better fix.

How about a pic of your fan/shroud/water pump set up?

[tkjr]

I have 1969 C10, 350 SBC. Truck has been overheating to 210 when sitting idle or just drifting speeds. I've replaced the radiator, replaced the thermostat with a 160*. Truck still gets hot. I've been told that maybe it just idles too slow and to adjust. When driving normal speeds it cools down so I DO believe it's a matter of air flow over the radiator. I purchased a few water pump but seems like a 'last resort'. I'll make sure shroud is sealed off well and maybe adjust idle.
Any other ideas?

[Stocker]

Originally Posted by tkjr

I have 1969 C10, 350 SBC. Truck has been overheating to 210 when sitting idle or just drifting speeds. I've replaced the radiator, replaced the thermostat with a 160*. Truck still gets hot. I've been told that maybe it just idles too slow and to adjust. When driving normal speeds it cools down so I DO believe it's a matter of air flow over the radiator. I purchased a few water pump but seems like a 'last resort'. I'll make sure shroud is sealed off well and maybe adjust idle.
Any other ideas?

There shouldn't be any need for a 160* t-stat, and using one may prevent your heater/defroster from giving you much heat. Stock t-stat might be 190* - 195* and will not cause overheating, especially if the cooling system is in decent condition. At any rate I would not run anything less than a 180*. FWIW, 210* is quite a ways from overheating when you have a pressurized system running 50/50 antifreeze water mix.

I think you're on the right track as to air flow and having a good shroud. What kind of fan do you have? A fixed-blade fan can cause your problem, and a functioning fan clutch with a 6-blade or better yet a 7-blade fan should fix it. The fan should sit right at the end of the shroud, roughly 1/2 way inside the end of it.

Pics would help....

[rockyrivermark]

Do you have a fan shrout?
that really helps.
Mark

[tdangle]

Idle and low speed running hotter is almost always air flow thru the radiator. If the radiator or block were plugged it would also run hotter under a load, since the engine is generating more heat to dissipate. Years ago I had a fan clutch go bad and while the engine was running, I could actually grab the fan blade and spin it backwards. (Don't try this at home as your mileage may vary, years ago I wasn't as cautious as today)

Just recently I had a water pump explode and take out my fan and shroud. New pump, and fan blades without the shroud the temp would climb at an idle, as soon as I was moving it cooled right down. Replaced the shroud and all was good again.

BTW: Never leave out the little pilot spacer when mounting the fan clutch to the water pump. At 5K rpm it may explode the water pump. Went thru 2 before I figured it out.

[truckster]

Is the fan connected directly to the water pump pulley, or is there a finned aluminum part between the fan and the pulley? It would probably be 8 or 9 inches in diameter.