I tried searching but couldn't find an answer. My 69 442 engine temp jumps to 225 when idling in traffic and starts to cool once I get going. I check the coolant reservoir and it was empty so I added some coolant, but nothing changed. Is this normal? What temp is too high? Fan seems to be operating normally.

 

Since a 1969 did not come with a coolant reservoir from a factory OEM build (you could install an optional dealer installed coolant reservoir; and some installed aftermarket coolant reservoirs) - simply adding/filling the reservoir may do nothing at all since most were merely puke tanks and did not siphon coolant back into the radiator. What you need to do firstly is remove the radiator cap (when engine is cold), run engine for 10 - 15 minutes and evaluate the level of coolant in the radiator and ensure the coolant is moving optimally through the radiator cores.

 

225 isn’t terrible, if it’s puking antifreeze into the overflow but not sucking it back in I’d replace the radiator cap.

Does the car have a shroud? If not, that’s a good addition. What kind of fan? If it’s a clutch fan, there should be a noticeable “roar” as the clutch engages. If not, replace it with a good thermal style clutch.

Since it cools down once the car begins to move, that suggests a low speed airflow problem.

 

Exactly. Oldsmobile motors can run hot. Just part of what they do. Especially if you are running air conditioning.

 

Good suggestions/statements yet the very first thing to do is open the radiator and actually view the amount of fluid - FIRST. This is a no brainer and must be performed before anything else is purportedly assumed to be a corrective action. No/Low fluid isn’t going to cool an engine at idle, in particular.

 

225 is high and since it recovers at higher speed you have an airflow problem. Do you have a fan clutch.

 

Really good system flush could really help also. Have you pulled the radiator and had it hot tanked cleaned etc? I have seen that make a big difference.

 

Never seen 225 in either of my 1969 Oldsmobiles.

 

225 is high but not a problem IF the temp stops there. If it keeps climbing, that's a problem. With a 16 PSI cooling system, the coolant doesn't boil until the temp is over 250 deg F. The first question is, do you know your temp gauge is accurate? Second, do you know your radiator is in good shape and not plugged? Third, what, exactly, has been done to the motor - these cars didn't overheat when new. Fourth, are all parts of your system working correctly (fan clutch if you have one, thermo vacuum switch on the vac advance line, timing, carb mixture, choke, etc)?

 

More correctly, you have a low speed cooling problem. It may very well be an airflow problem. It could be a coolant flow problem too. Is the overheating problem new? What, if anything, has changed? If nothing has changed externally, some part of the cooling system is failing. Are you filling the radiator/overflow tank each time you find it low? Hopefully that is not very often! Things that have to happen for proper cooling include adequate coolant, is it full. Is the radiator clear? No dust or grime build-up on the cooling fins? Is the fan clutch working? Can you hear a difference when it engages and releases? Have any of the shroud or surround been damaged or removed?

If as you say, nothing has changed, then something is beginning to fail.

Possibilities include a stuck thermostat. Don't pull it out, put it in a pot of water and put it back in! If you pull it out and check it, put a new one in. They are terribly inexpensive, even the good ones!
Failing fan clutch. These go bad. Let the engine warm up to the point it is pulling lots of air through the radiator, shut the engine off and see how much resistance there is to turning the fan. If it is easy to turn, try a new one.
Plugged radiator. Using Chiefs example, make sure the coolant is flowing well through the radiator.
Bad water pump. I have not seen this one but heard of pump impellers corroding away to the point they no longer force the coolant through the system.

Just a few thoughts...

 

As mentioned check the external radiator cooling fins for, clogging, corroding, being bent and having way too much paint on them. Had a car drive me crazy diagnosing these symptoms, the lower section of the external fins was packed with sand that was like cement.

Use an infrared thermometer to check the fin temps in many locations looking for cool spots indicating blockage.

If the radiator is original and is bad get it re-cored for originality. If you don't re-core it don't scrap it, members will want it including me. Please PM me if that is the route you go

Good luck!!!