I'm about to the point where im gonna put a for sale sign on my car, i just rebuilt the 350, nothing special basically a stock rebuild since im in school it needs to be half reliable right now, its not quite over heating but its damn near the 260 mark on the gauge. I just bought a brand new alum. radiator, 180 thermostat, new water pump etc. I know it doesnt help where i live in az its 110 degrees and not even june yet, but i dont understand y it wont run cooler like its supposed to. only thing i can possibly think about is the computer since the computer thinks its the stock 305 still i thought maybe i needed a chip so it would know its a bigger motor.

The engine is a 350 bored .060 over (360) stock heads, very very mild bump stick, stock intake and q-jet. nothing special not a 600 hp engine so why is it having a problem running cool? any help would be greatly appreciated.

 

Did this start exactly when you put the engine in?

Are you sure the timing is set correctly. All the gaskets were properly installed, etc?

Have you checked ALL the little stuff (including replacing the cap, no loose hoses, mostly or all water for coolant)

Does it happen when driving, or idling around town, or both? is your fan working? Is the air dam in place?

That should give you a place to start. I can guarantee that it isn't the chip giving you a problem if thats any help

 

yea the timing is set correctly, i used most of that black silicone stuff that gm uses for all of their gaskets, the air dam is in great shape, i just bought 2 electric fans that came off a 92 camaro i believe and they work great.

 

If youy can't answer everything i posted as well as add some other little stuff that i don't think of off the top of my head you ain't done looking yet. The dumbest little detail is usually the cause of all your cooling woes. I've been completely stuck on overheating problems in the past, and nothing worse than killing yourself overheating for a summer cuz you were too cheap to replace that radiator cap cuz it 'looked' good, or the 50/50 cooling mix just wasn't working in the rusted old engine, etc, etc.

You can either keep replacing parts, or start going over it with a fine tooth comb. One costs a lot of cash, the other time. Most of us have more of the latter....

 

Im sure its something that i just over looked, i forgot to add that it only happens when im driving around, at idle it stay about 210, the radiator cap is also brand new. I appreciate your help

 

How about the lower radiator hose collapsing at cruise/high rpms. Can and does happen. Does yours have the spring in it to keep from collapsing.

Could also be too much anti-freeze in the mix , if you guys even bother with out it out there, dunno, i wouldn't, AF is a horrible coolant, but i digress

Or also a worn impeller on the waterpump. If yours is old, or is a generic reman unit from a parts store i'd suspect it. Could even be something really dumb like they gave you a reverse rotation pump for a serpentine belt car.

Those would be my first guesses on an under-load/cruise overheating problem. Nothing can be written off though....

 

86,

I'll vouch for Ed's theory (like he needs any of MY support). I've had reman water pumps that have had almost no vanes on the impeller, and know I've had cooling problems because of it.

Other than what's been mentioned, the common causes of overheating are:

Lean operation (mixture control, vacuum leaks);

Late ignition timing;

Restricted exhaust;

Corroded cooling system;

Excessive load (dragging brakes, tight transmission);

Restrictions from incorrect gasket alignment;

Slipping pump belts;

Incorrect heater hose routing;

Sticky thermostat;

I wouldn't concentrate too much on the fans being the root cause, since they are basically ineffective over 30 MPH road speed. Ram air does all the cooling above that.

The thermostat change to a 180° is a good idea, but you should operate the fans at a lower temperature as well to take full advantage of that change.

Since your engine was recently rebuilt and you have a new radiator, I would presume that corrosion is not a problem. I'd still run at least 10-15% antifreeze in the mixture to keep the system clean and lubricate the pump seal.

It stays much cooler around here - we only occasionally top out at 105°F/95% RH, so I can get away with a 35/65 coolant mix (DexCool, of course) and my 180° stat and fan control keep the TPI at 205° at worst. I used to hit the 260° mark sitting in traffic with the AC on, but that was before the 180° stat and fan control.

Did you happen to get a stat with weep holes, or make a hole of your own? That can help eliminate entrapped air, and has the tendency to make the thermostat react just a little faster - but not necessarily cooler.

I'll also vote for replacing the radiator cap if you haven't already. For the price, it's worth the peace of mind.

 

If the gauge reads near 260* and it's not overheating,or running rough,I would check the gauge to make sure it's working.
When I bought my pickup truck the gauge read 260* when warmed up,but it didn't overheat or knock and ping at all so I installed a new gauge and found out it was only running about 210* tops....

 

That could be part of the problem. Boring out puts your cylinder walls closer to the internal water jackets. Isn't .060 over is pushing the limits a little bit?

Since it seems to run hotter while driving (under a load), the enging is working harder, thus more heat created. Most of that heat is being created right next to your coolant through the thin cylinder walls.

Old guys....comments.

RB

 

I think the temp sending unit for the guage is bad. Check all your connections to the temp guage, including verifying that you have a good ground. Everyone knows how factory guages suck, so I would try a different sending unit/guage setup. Screw it into the cylinder head...

I would try the old style thermocouple or the electric type...depending on what you can get.

It sounds like nothing on your combo should be causing this...Do check your rad carefully to make sure there is no debris, etc.

 

Definately check the gauge to make sure it's reading accurately. And like said, I would check the lower radiator hose, cause if it only happens at high speeds then the hose is a likely cause.

Also, check to make sure you're not low on tranny fluid, that could cause overheating too.

 

Thanks for all the help guys, i did forget to mention that the sending unit was just replaced, and i have 2 gauges, the one that was in the car and i got one out of a junkyard and they both are reading about the same. it could be the tranny fluid because i do have a leak in the tranny but i was going to get it rebuilt this summer also, I didnt realize tranny fluid could have such a big effect on engine cooling.
Thanks