Hey there, I'm looking at getting a '77-'84 98 to fix up. There's a couple I've found that are in the price range I'm looking at, one is a 307 and the other has a 403. I've read that the 403 is prone to overheating, how true is this? Once I get it fixed up I intend on taking it out on road trips, and living on the west coast there's a fair number of hills and mountain passes you'd have to go through for a great many destinations. Can a 403 handle something like that without blowing up? Is it possible to run the AC on a hot day while climbing up a mountain? What's your guys' experience with it? Thanks.

 

A 403 would be fine with a correct size, clean radiator. I would not want a 98 with a 307 especially on hills.

 

Very true, the 307 is somewhat wanting in the power to weight area......

 

The 403 was rated 320 lb-ft torque, which would pull a 98 up hills with ease.

 

The 403 powered the 12,000 lb GMC motorhome if that gives you any comfort...

The engine is in its glory, stock, properly maintained, and unabused. (Its simply not built as sturdy as earlier engines.)

I say reliable when in the right hands and used as intended.

403s over 307s always, same weight, same weaknesses, more power.

 

By the way I forgot to mention a 1977 403 98 is 3 seconds quicker to 60 MPH. Vs a 1980 307 98, coupe to coupe. While weighing 150 lbs more curb.

That can come in very handy on big city highways with short merges.

 

I wouldn't hesitate to buy a 98 with a 403 or a 307. GM used the 307 all the way until 1990 in full-sized cars and station wagons. Get whichever vehicle you can find that's in the best condition.

 

The 403 is fine. They only overheat when people rebuild them incorrectly. Leave it factory, and it is fine.

 

I had tons of overheating at highway speeds with an Olds 403 in a G body. I finally got it to 195 to 215. I can to realize it was air direction, I had the factory flaps in place, it had small 87-88 Euro grills. Once I installed the GN rad surround, it dropped temps a good 20 degrees. Get a big aluminum rad with dual 1" cores and either a heavy duty 6 or 7 blade clutch fan or good electric fans and you will be fine. You can also go the Flowkooler or heavy duty factory closed impeller water pump and Robert Shaw thermostat. Also don't under drive tge water pump on a 403. Also do dual exhaust if you can get away with it. It will widen the gap even more between a 403 and 307. I also like the looks better of the late 70's vs 80's 88 and 98 RWD cars, so another positive for me. Our 81 Delta 88 4 door was a great car, Ok power and good mileage with 307/250C/2.41 combo. I later got beat in a race by a Mercury Mistake, I mean Mystik. The factory, already restrictive cat was plugging. He wouldn't race after removing the cat. A 403 car wouldn't have lost that race. Good luck.

 

Where did you read this?

The 403 was used on tens of thousands of Oldsmobiles and other makes for the 1977 through 1979 model years. If there were an overheating issue with this motor, it would have been well documented and well known by now.

I have both a '77 and '78 Toronado, each with a 403 (the only engine offered), I have temperature gauges on both, and both run all day long at 180 to 190 F.

Buy the 98 with the 403 and remember, as Edgar Allan Poe said, believe none of what you hear and only half of what you see. (The actual quote is "Believe nothing you hear, and only one half that you see.")

 

A way to circumvent the weight issue is to use a numerically higher rear gear. Any axle from 77-96 B body sedans would work. 91-93 with tow package usually had 3.23 or 3.42.

I agree with everyone else though. The 307 is not the right fit. 403 with some early heads and an appropriately sized radiator, 180* thermostat shouldn't have overheating issues.

 

Some random article came across. I figured it would be best to verify that with people here that have real world experience.

Thank you, this has been very helpful. I'm going to try and go for the one with the 403, just waiting on pics to verify the condition of the body. If that checks out I'll proceed with the rest of the due diligence and acquire it. Wish me luck!

 

Everything that article says is true, specifications-wise. Doesn't mean that every 403 overheats or even that a lot of them do. He shows a photo of a coolant passage "gunked up" with rust. Fine. Any engine with gunked-up coolant passages is a candidate for overheating.

The 403 has its limitations, but, as I said and as the article lists, the 403 was installed in lots of Oldsmobiles, Buicks, and Pontiacs back in the day, and it served perfectly well.

 

I have a 403 in an 87 442. Ran it for several years with the stock 307 radiator, 5 blade clutch fan, and all of the factory baffles in place. This car has operating AC. No overheating. I did add a 7 blade fan and new standard duty clutch this year, and it stayed cooler at low speeds, but not necessary.