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Been having issues with my 71 442 overheating when highway driving. Getting almost a 20 deg drop on radiator from thermo cap to bottom of rad. Trying to figure out what could be going on. Had mechanic do a cooling system flushed last year but decided to do it myself again now as it seemed dirty. I’ve run several cycles of flush. Prestone, Blue Devil, and Thermocure with several fresh water flushes between. Since last one I’ve done several more fresh water flushes using the T fitting on heater hose. Run it until water coming out the radiator top is clean. However if I leave just water in and then run the car up to temp I keep getting dirty water when I go to drain. Thermostat was removed for the process. Picture below is what drained water looks like. Not sure what could be going on. Expected it to be closer to clean. Am I missing something?
Your radiator is probably fooked. If it is a stock style radiator you can take it to an old school radiator shop and have it boiled out and flushed. Or you can buy a newer aluminum two row radiator with wider tubes that is more efficient. Also make sure your fan shroud seals tightly to your radiator. And that your fan clutch (if you are running one) is working correctly.
Running a HD fan clutch. Car has AC. Put in new water pump past two years.
Radiator is a 4 row brass. With the temp drop I was seeing didn’t think it was bad. Not sure it’s age. Had the car for a few years now. Previous owner had it for 20+ and didn’t put many miles on it.
The number one reason why cars "overheat" is aftermarket gauges. Most are really not over heated unless the factory gauge is showing hot. 210 deg is not all that hot for a BBO.
That does look dirty. Try flushing it with the block drain plugs removed, not the frost/expansion plugs, the threaded 9/16" hex head plugs. There is one on each side of the block near the motor mounts. If there is debris in the block it is difficult to get out via topside flushing because you are fighting gravity as the debris wants to stay in the bottom of the block.
As always, use reasonable force trying to remove these plugs. If they are really stuck you may be better off leaving them and removing an
accessible frost/expansion plug.
Good luck!!!
Last edited by Sugar Bear; October 23rd, 2022 at 09:23 AM.
Speed will have a bearing on engine temperature. I just came back from a car show that was about 50 miles away. It is in the mid 80's today. I had the AC on and was running about 80 most of the time. The 455 in my 75 Olds was running about 210°. As soon as I slowed down after my exit it dropped to about 180=190°. This is per the factory gauge. Engine and cooling system are both in good condition and car is completely stock.
When you say over heating, what temp is it reaching while your drive? What is the temp when you're idling for a while?
Idling seems fine. Around town driving seems fine. Usually under 190 deg. Will try again today extended idle.
I do have an aftermarket Bosch thermo mechanic put in to give idea of temps while troubleshooting. This has been an issue we've been chasing since I got the car a few years ago.
When driving highway, say speeds 65-80mph temp starts to climb. Usually hear fan roar kick in 195 to 210 deg. Even seen this on speeds 50-65 but fan keeps it below 210. Over 65 it can't keep up and keeps climbing. Car has TH400 and 3.08 rear.
When I got the car it didn't have a fan clutch, had a smaller fan and shorter water pump. Car was getting too hot even with in town driving in Florida. Got a heavy duty fan clutch, and HD water pump with correct length. Fan was more difficult as ones I've seen at the Olds parts shops are too small. I think the shop manual called for 19.5" Found a mid-70s Corvette 19.5 inch 7 blade which seems to pull a lot of air.
With the dirty water I was/am worried maybe a head gasket leak. Going to drain oil to check how it looks. Water though has an antifreeze smell and leaves greenish residue when it dries on the pan and bucket I am collecting it in. Car otherwise seems to run fine.
If it’s getting hot at highway speeds, make sure all the shrouding and baffles are in place. It’s possible the air is going around the radiator and not thru it.
That does look dirty. Try flushing it with the block drain plugs removed, not the frost/expansion plugs, the threaded 9/16" hex head plugs. There is one on each side of the block near the motor mounts.
Thank you, that was very helpful finding the plug. Bolt had hard light yellowish stuff on tip in block and hard deposits under that too.
Originally Posted by oldcutlass
The fan does nothing at highway speeds for cooling. When was the last time you checked your dwell (if still using points)/ timing settings?
Haven't yet quite figured out setting the timing. Had my mechanic do it after converting to Pertronix. I used to believe the fan didn't do anything at higher speeds but think that is only true when the system is otherwise functioning properly. At 50-70 I've seen the temp gauge use to start to drop when I hear the fan roar start when it was otherwise climbing beforehand.
Originally Posted by matt69olds
If it’s getting hot at highway speeds, make sure all the shrouding and baffles are in place. It’s possible the air is going around the radiator and not thru it.
I remembered reading that on the forum a year or two ago when I was trying to troubleshoot. Top side ones were missing which I added. Can't remember if ones were missing other places.
Current update.
I do appreciate everyone's help and suggestions. Because of all the hardened crud I saw I ended up running a gallon of vinegar through it and letting it sit overnight. Prior to this I've done cycles of Prestone AS105 (x2), Blue Devil 3in1, and Thermocure all overnight after running the car with multiple water flushes between and was still getting very dirty water and car still overheated. Vinegar got a lot of junk out. Water was very dark and had small debris. Did a few fresh water flushes with running the car in between and got a dirty rusty water. After the 3rd fresh flush ran the car on highway and it is much better! Stayed right around 210 going 75-85mph and came down to 190 quickly once I got off highway. Ambient temp was in mid 80s, didn't run AC. Drained the block and still got dirty water. Much happier now but will still probably do some more flushes until I get something approaching translucent. Can't believe all the crap that came out of the block.
Some engines where not fully flushed at the factory and had some of the sand from the casting process remain in the deep recesses of the block. If this engine was rebuilt, perhaps it was not hot tanked properly.
This stuff works really well. We use it at my shop when we have a diesel engine that the oil cooler failed and contaminates the cooling system. You can get it at your local Cummins dealer or at a lot of diesel specialties shops. Just don’t leave it in your engine overnight. Follow the directions.
Next time you flush the engine, remove the block plugs from the side of the block, down by the engine mounts. If there is nasty crud settled down in the water jackets, you will be fighting gravity trying to flush the crud up towards the radiator.
October 22nd, 2022, 07:44 PM
