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Do bored out 425's overheat more easily?


65VerdeGS
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Is a 425 cu. in. engine more likely to overheat after its been bored 0.30 over?

I had my 425 rebuilt recently. This engine never overheated in the 27 years I owned my Riviera, regardless of the weather. After I rebuilt the engine I drove the car to California. In Medford Oregon the engine overheated (HEAT light came on) as I drove through a traffic jam in 95 F weather. My car does not have A/C. I stopped and allowed the engine to cool off before carrying on. Then it happened again when stuck in traffic in Southern California.

Should I replace the radiator with a higher capacity one?

What is your experience with this?

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Is a 425 cu. in. engine more likely to overheat after its been bored 0.30 over?

I had my 425 rebuilt recently. This engine never overheated in the 27 years I owned my Riviera, regardless of the weather. After I rebuilt the engine I drove the car to California. In Medford Oregon the engine overheated (HEAT light came on) as I drove through a traffic jam in 95 F weather. My car does not have A/C. I stopped and allowed the engine to cool off before carrying on. Then it happened again when stuck in traffic in Southern California.

Should I replace the radiator with a higher capacity one?

What is your experience with this?

Hi Alex,

A fresh rebuild will always run hotter than before the rebuild. In fleet work, because your experience is so common, it is typical management policy to install a fresh rad with an engine change.

There are all sorts of possibilities in your situation (50 year old car) from a bad temp sending switch to a marginal rad, etc. I would measure/confirm the actual operating temp of the engine instead of relying on the idiot light and work from there.

Tom

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You are experiencing what I've seen many times over the years in the auto repair

business. When you are dealing with the largest bore biggest displacement version of a given

engine block and then you bore it out even more than the factory did, you wind up with very thin cylinder walls and an overheat condition. On Pontiac 455 engines with an overbore, they tend to run hot. 428 Fords with an overbore ditto, 455 Olds engines ditto and so on. I've seen it many many times, and I always warn the customer up front before a rebuild.

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OK Riviera People: I have 3 425s .30 over. As long as the cooling systems are happy there aren't any problems. With today's engine rebuilding only some get the hot tank treatment because either the machine shop doesn't have a tank or has a much less corrosive solution to be in VOC compliance. The rebuilders need to really get the nooks and crannies. The caca from the block can work it's way through everything and cause problems. Remember, these are 50 years old now....not 12. Mitch

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I saw the words 'Southern California' so I recommend a four-core re-coring with a higher-efficiency (higher fin count per square inch) core and a fresh, high-quality coolant mix. Also, check the fan clutch operation (if you have one) and fan blade condition. If that doesn't solve the problem, then you know it's not the rad or fan assembly. Process of deduction may apply here.

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Since it does not have A/C ...... does your car have a Fan Shroud, if not, I would add one and when replacing the radiator go for the 4 row core and make sure your fan clutch is working properly. That's my two bits worth. Lastly the timing has a lot to do with the operating temperature. Paul

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