273 Overheating problem

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67bluefish

67bluefish

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Hi all,

I recently had my 273 rebuilt (bored .030" over, slightly lumpier cam, upgrade from 2bbl to Holley 4bbl, dual exhaust) and am now having overheating problems that are keeping me frustrated. I had the radiator re-cored as well, so I'm hoping that it is not the problem. I can go about 30-45 minutes at highway speed, 2500-3000 RPM with no problems. However, any more time on the road than that and the temp. gauge starts to creep higher than I want it to (200 degrees+, whereas before the rebuild it held 180 with no problems). I can put the heater on high, but that's only a band-aid, it's not solving the problem.

Any ideas out there? Something as simple as changing the coolant, or a different rad. cap - currently a 16lb cap, I believe - ? I'm pulling my hair out, as I really want to get out on the road!
 
what kind of temp. on the thermostat are you running? drop it to a 180. does your current radiator have a shroud? can it be fitted with one? if so get one it will help. what type of fan are you useing? 4 blade? 5 blade? change it out to a 6 or 7 with a thermostaic clutch. this will also help. recored radiator you say? did you go with larger core tubes and tighter rows or just add another core? how is the waterpump? try to start it cold with the cap off. stick your finger down in the radiator and wait for the thermostat to open. if the flow from the water pump in non existant then water pump should be checked for an upgrade or replacement. you should feel and see the antifreeze moving around when the thermostat opens up and starts to circulate.......
 
It's a 180 thermostat, still has the original 4-blade fan, no thermo. clutch. There is fan shroud, but I'll have to check how much it's actually helping (that is, close enough to the fan to be effective).

I'll have to check my records, but I believe that I had the rad. recored, but I didn't increase the rows at all. I know it will help, but is that a necessity? The load on the engine hasn't increased enough for an increase, has it?

As for the water pump, that is a possibility. I'll have to take a peek inside this week.

Thanks for the suggestions.
 
I'd start with the basics, test the thermostat. Get an accurate thermometer and check the opening temperature, stick the thermometer in the radiator and watch for the coolant flow in the radiator . If that checks okay, then try changing the fan and installing a shroud. The other consideration is the pump and fan pulley, are they matched to one another ? An AC pump has a SMALLER impeller and pulley than a non AC pump, mix them around with the pulleys and you have inadequate flow.
 
how much over 200F?

200 is not a big deal

your boiling point would be over 250F

your running temp is going to increase...more compression and thinner cylinder walls
 
Well, I've been swamped at work, so there goes any hope of fixing this before the weekend. However, I appreciate your responses - I'll certainly check the thermostat this weekend, just to make sure. I'm hoping that the water pump isn't suffering - after paying for an engine rebuild, I'd like to keep the engine expenses down for a while (wouldn't we all?).

Sanguine, you have a good point - I hadn't thought about how much of an effect thinner side walls and the higher compression would have.

As for an exact temp. number, I couldn't tell you - '67 gauges don't tell me much, just that it's above "Normal," or whatever term you give to the middle line on a temp. gauge.

66dartgt, the car was originally an A/C car, but I've removed the A/C unit. However, if there were two different size water pumps (as I understand you to be saying) then I still have the A/C-size water pump attached, directly to the fan. Is this what you are talking about?
 
id get an aftrmarket gauge bluefish, and see where it is exactly..factory gauges are notoriously inacurate...

i dont think its anything to worry about

if you want to bring it down a bit consider upgrading that 4 blade fan...the A/C water pump should have increase flow compared to a stocker
 
Same thing happend on my .030 over 273. I changed from a 4 blade non-clutch fan to a 6 blade thermo- clutch fan with a shroud and that fixed it. It droped the running temp to the low normal range.
 
If you are running the correct pulley for AC with the AC pump you are fine. The issue lies with the fact that mopar used small pump impellers with small pulleys (AC set up) and large impellers with large pulleys (non AC set up). Most people assume that an AC pump is spec'ed for higher flow - NOPE, they are matched to the pulley set up - period. If you want a higher flow rate, use a non ac pump with an ac pulley. Check your service manual in the cooling section - its all right there in black and white. Hope this helps !
 
Most people assume that an AC pump is spec'ed for higher flow - NOPE, they are matched to the pulley set up - period. If you want a higher flow rate, use a non ac pump with an ac pulley. Check your service manual in the cooling section - its all right there in black and white.
Click to expand...

you learn something new everyday :)
 
Let the motor loosen up and put a good temp gauge in.
all above is go advice but I have always had High temps on a new motor.
Hope you can get to it this weekend.
 
I've been having some heating problems and noticed my front pulley (attached to water pump) is smaller than other cars. I think it's from an A/C car. I'd say it's about 1 inch smaller in diameter than the others I've seen.

I'm guessing this makes the water pump rotate faster, thereby making the coolant flow faster and not cool the motor as well, right?

How much difference would a larger pulley make?

I also have a pinhole leak in my radiator, does this affect the pressure and temperature?
 
One other item to check or replace is the radiator hoses. If they are old and soft sometimes they have a tendency to collapse when flow pressure increases. Mike
 
Ah, the wealth of knowledge here is always refreshing! Thanks for all of the help and suggestions, folks. My first attempt will be with a new temp. gauge, and after that I'll move on to hoses, then pulleys if necessary.

However, it will be awhile before I get to it, as I'm out of town at the moment...oh life, how you keep me from my car!
 
Did they put a new temperature sending unit in rather than just use your old one? Might not be the right one. They did the same thing to mine and it hasn't read correctly since. It always shows higher temp no matter what and I can just feel the motor and it is not running that hot. I'm going to eventually do away with the factory and go with a after market so I know it is right then.
 
Don;t forget to check your radiator cap. needs to be able to built pressure to keep from boiling also. Just a thought that I didn;t see mentioned above. I do agrre with getting a good gauge. There is no factory gauge out threre that I would trust. Good luck!
 
Just to let you know bluefish...it must be something small or EZ you can change to get back on track. Although, I'm from western BC my 273 was also re-built 30 over. Had the 16lb cap, 273 small rad 17x19 (or close) and the orginal 4 blade. I didn't have a AC unit or power steering however.

Never had any temp issues except once or twice I over filled the system and she was pissing out the bypass hose for a tad.

I did record high once and pulled my sender unit, it was pitted/worn some. After swapping out my reading was back to normal...(needled centered)

Hope you work something out and it's a small change! Oh sorry, not sure of my degree thermostat.
 
After you've verified the temp, try running it without the thermostat and see where the temp ends up. Everyone else has about covered everything else. Does the engine have good power? If so it's probably not timing. Good luck Howard
 
Plenty of power, no problem there.

I'm hoping to check the sending unit next week, or possibly this weekend when I get some free time (wouldn't that be nice!)

Thanks for all of the help so far, folks!
 
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