My 1975 buick 350 lesabre only seems to overheat on the freeway if i go over 55.and you can hear and see the overflow tank bubbling. .Once i get off freeway it will drop back down to 190-200 and my mr gasket radiator cap also has a built in temperature gauge will read 160-170..ONCE it went up to 230 but quickly went down. . I can ride around all day on city streets for 4-5 hours with temperatures in high 80s and low 90s and it will not overheat at all. So i have put a new thermo clutch fan on it. Still same issues. Changed out lower hose for new one Still same issues. I flushed the radiator out 5 different times and made sure all the air is out. And of radiator was bad wouldnt it overheat on stop and go traffic too? Im not losing antifreeze because it still be full. Changed out thermostat 3x and even tested them on my stove in water and they open up. Its no anti freeze leaking out the weep hole and seems to work when i squeeze the upper hose but i ordered a new water pump just to swap that out so that will be my next step and shouldnt the surge from the water pump be strong when i squeeze it and let go or light..it feels light.. My other question is if i had a timing issue wouldnt the car die? It never stalls out and runs perfect except for when im on the freeway. ..and what i mean it runs fine on freeway except for the overheating
I checked my timing Timing gun says 10 Markings on engine is at 0 at idle When i rev it up when timing set at 10 on gun.. Markings on engine at 12 When gun at zero and engine at idle it. Markings on engine at 8 This with vacum off
When i set the gun at 30 and rev it up the markings on the engine line up at 0 so i know i didnt set my timing wrong. Should i advance it to 32 to see if that fix my over heating on the freeway or my timing not the problem. And the distributer brand new
Looks like it the original radiator. Im going order a new one and put that in first because it easier then the water pump. And see if that works..
If it is one of those old black looking ones they put in them, and even if it was replaced 20 years ago there is a good chance it is clogged. When I replaced mine I lifted the radiator by hand, it was heavy as hell, surely clogged badly. I don't know if this is a true test to tell if clogged but I was told that after a run like what you are doing get off the hwy and pull over and shut it off and fell the rad, I was told that the radiotor should be cooler at the bottom I think, then the top. If not and it is hot everywhere it is clogged. Someone will correct me if this theory is wrong.
I had one of those Mr Gasket radiator caps once It wouldn’t hold any pressure so I threw it out. For what it’s worth, I don’t think the lack of pressure would make you run hot, but if the cap doesn’t hold pressure like mine did when it cooled it wouldn’t pull the antifreeze back Into the radiator so the coolant level would be low.
Those temp caps are garbage. Get a champion (or other well make brand) 2 core rad with 1" tubes. Cools better than a 3 core with smaller tubes. Aluminum is more rigid than copper so the tubes can be bigger without collapsing. Flush your cooling system too, as well as the heater core. Replace the thermostat with a 180 or 195, and make sure your fan clutch is good. If it overheats at idle there isn't enough fan to draw air through, or the rad is clogged. If it overheats on the highway, the rad is clogged and all that hot coolant is just sitting there. Also your rad hoses will be rock hard.
Only overheats if i go over 55 on the freeway...it can idle all day long no issues and drive all day long but once on freeway over 55 it will start overheating about 15 minutes into the drive. Fan clutch is new
Then rad is the problem. The fan clutch ceases to be as effective at cruise speeds because of all the incoming air. But it can't radiate the heat to the surrounding atmosphere if the rad is clogged with sediment or build-up or mineral deposits because the coolant will essentially get stuck in one area of the rad insteas of flowing through dumping off some heat and going back to the engine to take away some more.
OR perhaps your lower rad hose is sucking shut on the highway. Its quite common. Rev it up and watch the hose.
