[One Grand Am]

'73 GA All Stock. Having an issue with it getting hot at highway speeds. Slow traffic driving - never an issue.
Things I've done and replaced:
Flushed engine until good, clean water came out.
Fan Clutch.
Radiator.
Heater Core.
Water Pump.
Thermostat - 180 degrees.
When I put the water pump in, I clearanced the water pump plate. New 'o' rings in the crossover tubes. Cast iron impellor.
Timing is on and right. Cleaned weights in distributor, new springs. It gets up to 215 - 220 degrees. Also have an after market gauge set that verifies that temp. Is there anything that I am overlooking? Any suggestions? Thank You!

[rexs73gto]

This may sound stupid but did you make sure the fan is on the correct way so it pulls instead of pushing aginst the air flow. The fan blade can be bolted on backwards. Also because it's seems to be running hot at speed have you also made sure you don't have an air pocket in the block? Make sure the coolant is FULL. let it run a bit with the raditor cap off so ALL the air gets out of the system. It may take awhile , as much as 1/2 hour to completly get rid of the air in the system. You may speed things up by making sure the right front side of the car is jacked up higher then the rest of the car so the air has to go to the high side of the raditor.

[Brian Baker]

Do the temps drop back down once you stop running at highway speeds?

[77 Canamman]

Does it have the factory plastic air dam under the front of the car, bolted to the radiator support? If it is an A/C car, have you cleaned the A/C condenser unit with a garden hose? A lot of debris/bugs can affect air flow. Is the fan shroud 100 percent intact? Lean carb mixture can cause a car to run hot. Any exhaust restrictions or poor performance at all?

[se428bandit]

Do you have a 3 or 4 core radiator. I just went thru the exact same thing with my Ventura. I had a 3 core and changed to a 4 core and my temps never go pass 195 on the highway now even in the high 90's degree heat.
What size pulley is on the water pump? If it's pumping the water to fast thru the radiator a bigger pulley on the waterpump could slow it down a bit.

[One Grand Am]

First of all, Thanks for all of the suggestions. I really do appreciate them.

I checked the fan, it is pulling, (not a stupid question!)
Could have an air pocket, but I've put 5K miles on it since doing the work. Will let it run with the cap off though to make sure that's not it.

The temp does come down when not at highway speeds.

It does have the small air dam under the rad support. It is A/C equipped. I haven't cleaned the condensor but I will. But to look at it, it seems clear of debris. Fan shroud is in tact and 100%. I will fatten up the carb tomorrow. New exhaust and very respectable performance.

It does have a 3-core rad, that's what I took out, and assumed it was o/e, and figured my new one would be sufficient. The water pump pulley seems to be about 6.5".

Again, THANK YOU, Chris.

[moontower69]

you said you flushed your engine but you might want to rod out your radiator too (flushing won't do it). My 74 Lemans had the same issue on the highway and i solved it by rodding out the radiator (crud was restricting flow), sounds like you have a water flow issue if creeps only on highway only....JMHO

[Grand73Am]

I believe he said he put in a new 3 core radiator, so it shouldn't need rodding out.

Do you have a spring in your lower radiator hose? Originally there's a spring. If not, and the lower hose is soft, it could be collapsing at speed, blocking off flow. So, that's something to check.

Also, did you install a new radiator cap? If not, it could be bad. And use one that's about 16 lbs.

If you're running ported vacuum for your dizzy vac advance, switch to manifold vacuum. Runs cooler and better.

[One Grand Am]

I replaced the radiator and heater core after I flushed the system.

I did put new hoses, with the spring in the lower hose, new rad cap too. I will change vac advance hose connection to see if it helps.

Thanks so much!

I'd like to share some photos, but I don't know how to get pics from my computer to here. Easy tips would be appreciated!

[Brian Baker]

My Can Am does the same thing, I just live with it, or not drive it so hard and keep highway speeds to 65 or less. It's likely a timing and/or fuel issue at speed. Check your timing curve from 2000-3500 rpm and see where total timing falls in 200 rpm increments. My guess is you've got too much timing at highway cruising speeds.

[zeebo]

what make of fan clutch? what is your coolant mixture? should be 60% water 40% antifreeze. run a hayden 2747 or 2797 super duty fan clutch...check for proper air flow through radiator, and make sure there is no air in the system. not all thermostats are alike...it should cool down a few degrees when up to hiway speeds, not be heating up. what are the clearances on the water pump?

[One Grand Am]

I'll check the timing at the higher rpm, I had a hunch that it could be in the timing. I fattened up the A/F screws about 3/4 turn each.

I don't know the make of the fan clutch, got it from Napa. Coolant mix is good to -37degrees. I've got good air flow, can see through condensor just fine. I've clearanced the water pump plate to just a few thousand. I'll get busy on these things tomorrow. Thank You!

[Jim Cody]

One thing I have always done when filling the system with radiator fluid is to fill the block thru the thermostat opening. Fill it up until level, then put the thermostat in and then install the housing and the hose, then fill the radiator and add to the overflow and run and fill as needed.

[zeebo]

remember, antifreeze doesnt cool...water cools....antifreeze is just what it says....antifreeze and antiboil protection, along with helping take the surface tension off water, and as a lubricant. more antifreeze doesnt mean more cooling; just the opposite...


i cant tell you the amount of times i have heard "i run straight antifreeze; itll never get hot!!" lol

[Brian Baker]

Originally Posted by zeebo

remember, antifreeze doesnt cool...water cools....antifreeze is just what it says....antifreeze and antiboil protection, along with helping take the surface tension off water, and as a lubricant. more antifreeze doesnt mean more cooling; just the opposite...


i cant tell you the amount of times i have heard "i run straight antifreeze; itll never get hot!!" lol

Well, to be more accurate, glycol based antifreeze is still a coolant, it is just not as efficient as water, which is why you don't (and shouldn't) need to run more than a 50/50 mix with water.

[One Grand Am]

I run a 50/50 mix of antifreeze/coolant and water. Need that kind of antifreeze protection because of the climat that I live in. I did add some "Water Wetter" and I put in a Mr. Gasket high flow thermostat. It dropped the temp a few degrees, but it still builds heat at speed. Had a couple guys ask about the condition of the transmission and if I was still running an egr valve. I got rid of the valve. Tranny works fine. I don't think its getting that hot, but I don't have a temp gauge on it either.

[rexs73gto]

I had a slight cooling problem with my car just about a week & a half ago. It got hot on me while I was trying to adjust the timeimg in the driveway. I thought it was a stuck t--stat. I wasn't sure if it was a stuck t-stat or a bad raditor cap. I replaced the t-stat & when I went to take off the cap it came off not to hard but ok. I filled everything back up & when I put the raditor cap back on ithe new one fit very tight & it overheated no more. I think it was more the caps fault & not the t-stat. While you've been doing all this have you replaced the raditor cap at any time?? Do the least expensive thing first & go down the list. Have you changed the cap yet?????????

[OZZIEVILLE 67 2 door]

I'll have a stab,,
Try a 160deg high flow thermostat..
I had one in my Bonneville and it would not reach 150,now running a 180..

[Brian Baker]

Originally Posted by One Grand Am

I run a 50/50 mix of antifreeze/coolant and water. Need that kind of antifreeze protection because of the climat that I live in. I did add some "Water Wetter" and I put in a Mr. Gasket high flow thermostat. It dropped the temp a few degrees, but it still builds heat at speed. Had a couple guys ask about the condition of the transmission and if I was still running an egr valve. I got rid of the valve. Tranny works fine. I don't think its getting that hot, but I don't have a temp gauge on it either.

You should not be using the Water Wetter product with anything but straight water. Using it with a glycol based coolant could effect the additives in the coolant.

[Brian Baker]

Originally Posted by rexs73gto

I had a slight cooling problem with my car just about a week & a half ago. It got hot on me while I was trying to adjust the timeimg in the driveway. I thought it was a stuck t--stat. I wasn't sure if it was a stuck t-stat or a bad raditor cap. I replaced the t-stat & when I went to take off the cap it came off not to hard but ok. I filled everything back up & when I put the raditor cap back on ithe new one fit very tight & it overheated no more. I think it was more the caps fault & not the t-stat. While you've been doing all this have you replaced the raditor cap at any time?? Do the least expensive thing first & go down the list. Have you changed the cap yet?????????

Yup...if you have a cap that doesn't seal, it will build no pressure. With no pressure, water will boil at 212 degrees, and the closer you get to 212 degrees, the more you will boil the coolant out of it with no pressure.