Overheatin 60'

[don whitehead]

Just put my motor back in. Rebuilt, balanced, 283 270hp. Everything is new/restored from the crank, cam, pistons, waterpump, carbs, lifters, etc. I even went for the new DeWitts top tank aluminum bigtube radiator. 5 blade clutch fan, 160 hi-perf thermostat. As long as it is moving above 20mph, it stays at 160. When idling it creeps up very slowly to over 210. I have dexcool and even added some wetwater. Engine has about 300 miles on it. Timing at 10deg.
Even replaced the fan clutch.
Any one had experience with this. Gonna try the timing next?

[Jack H.]

Re: Overheatin 60'

First, I presume when you report exact temp figures you're taking them from the dashboard temp gauge? This system is notorious for being inaccurate, I suggest that ALL who are experiencing 'hot' engine Corvette, get religion up front and use an accurate measuring device! It's easy to chase your tail trying to fix a problem that simply ISN'T real....

Shoot the bottom of the outlet rad hose with an IR thermometer (or, lacking that, tape a good oven meat thermometer to the bottom of the hose making SURE you clear the fan blade!) to get confidence in your on-board reporting system (sender, temp gauge).

Things tend to point to air flow through the rad. Which would point to the fan clutch.... But, 210F is NOT an overheat condition (that's marked on your gauge; it's up in the +230F range). Plus, with a freshly rebuilt engine you should expect it to run 'tight' until the piston rings and bearings fully seat (approx 5K miles).

It's quite possible you don't have a bona fide overheat situation.... But, get a 'second opinion' from that calibrated thermometer to be sure.

Why? Well, if your car is factory concours you've got a generator vs. alternator. At idle, the gen is probably NOT charging the battery causing B+ rail to fall (down from 14V range to +12V range).

Since on-board temp gauge is actually an ammeter in series between B+ rail and ground through the variable resistance of the temp sender, when B+ falls (there's no solid state voltage regulator on the dash instruments as in later cars) current flow in this branch circuit falls in lock-step (assuming fixed resistance/constant engine temp). Therefore, you'd logically expect the temp gauge to fall a scootch, instead of rise. It could be the 210F you see on the cockpit gauge at idle is actually LOWER than actual! A double check will help all sleep better at night....

[don whitehead]

Re: Overheatin 60'

Thanks Jack. I checked the gauge with external probe on the manifold inlet. It read 200 when the gauge was 210. Its getting warm. Even the sound of the engine changes when it starts to heat up. I thought with the DeWitts rad this would not happen. With the prior engine(Still duntov cam, single quad, no powerpak heads), even in the summer, never went over 200(same gauge & sender) even with the old brass radiator. How much hotter will a tight motor run? Should I try and retard the timing?

[Loren L.]

Re: Overheatin 60'

I had the same setup (except fi) at the NCM Labor Day 2000 and it took 25 minutes of idling to get my guage above 180, so I'll agree something is wrong.
Verify the timing first - do we have the correct balancer and timing chain cover so that we KNOW the timing mark we're reading is correct? Once that's verified, start with the simple stuff - like a loose belt, the fan mounted backwards
(don't laugh - it happened to a friend and 10/15 years ago, I saw one on the NCRS judging field, contending for a Duntov......), are we sure that the radiator is full, etc. Good luck.

[John H.]

Re: Overheatin 60'

Something is awry somewhere - I rebuilt my '57 283/270 five years ago, exactly as you did (except the '57 uses a direct-drive 4-blade fan, no clutch), with a re-cored original copper/brass radiator, and it runs at 180 (I.R. gun-verified; best tool I've bought in a long time) all day long, idling or on the highway - will also run at 160 with a 160 'stat, but I changed it to a 180 shortly after putting it back on the road. Retarding the timing will just make it run hotter, especially at idle. I'd verify TDC with a piston stop to check the index mark on the balancer (and the timing tab) and go from there, including mapping the advance curve with a timing tape or dial-back timing light (another indispensable tool); if your centrifugal advance isn't working properly (weights stuck, etc.), timing could be retarded at highway rpm, which will also make it run hot. Start with the basics and work your way up to the answer - you shouldn't have a cooling problem (especially at highway speed) with that radiator.

[Paul Rose]

Re: Overheatin 60'

If all other things are checked, try checking for a leaking head gasket. This will make the heat creap up as you say. It can be ckecked with a simple tester that looks for exhaust gases in the the rad neck.If there is no exhaust in the coolant you are safe on that side.

[Terry R. Payton]

Re: Overheatin 60'

Don- I had the same problem w/my '58 283/290 Replaced almost everything to the tune of many $$$. Got some great advice from this board(thank god for this board)anyway,turned out to be nothing but the thermostat...and it was replaced twice!what are the chances of two bad thermostats? I'm told by some pros that these little devices we depend on so much can be defective alot-so, good luck. Would love to hear your outcome.

[don whitehead]

Re: Overheatin 60'

Thanks. Most folks I speak with say it could be timing or the motor is so new its got a lot of friction. I get different answers about the timing and which way to go to run cooler. You feel retarding it will make it run hotter? I did notice a little run-on a couple of times, not always, which sometimes indicates too far advance. Its a re-built 891 dual-point distributor, runs dead on at 160 above 20 mph. Head gaskets are all new.
Don

[don whitehead]

Re: Overheatin 60'

Terry,
You said that your thermostat was causing you to overheat at idle? What was happening? Not opening far enough? If it was not opening at all I would expect it to overheat at speed also, not just idle? Mine runs at 160 over 20 mph.

[Terry R. Payton]

Re: Overheatin 60'

Hi Don-yes, it was the strangest thing. Temp would rise >220 at idle. At speeds, temp would back down, but not much. All this after replacing thermostat x2. So, the deduction was that both thermostats probably were not opening-again, what are the chances? anyway, the third thermostat is fine. I must say, all this after replacing radiator, switching to 6-blade fan, checking and rechecking just about everything....from timing to heater core etc....it was maddening! Terry