This motor only overheats on the highway and not in town, running at 3,000rpm will make it overheat in 15-20 minutes, if just cruising in town at 20-40mph it is fine but if you hammer the throttle and hold it for 5-8 seconds it will heat up by 5 degrees just doing that. It is running a 160 thermo which is working, big radiator and dual electric fans, 13lb radiator cap, radiator has good flow and I have even tried water wetter. This motor will hold 180-185 for a while then just takes off quickly to never never land. HELP PLEASE..

I think someone else will say the same thing, that there are a ton of posts on the site to search for on this subject, including my own.

My car (468) was doing the same until I adjusted my timing, it was severely retarded.

I now have a 20" flex fan and 180* thermostat in the car and she very rarely goes over 185 now. Was hitting 210+, got scary a couple times it went over that.

Good luck.

Welcome Mark. I play a little game here. When a post is headlined to have a overheating problem I tune in looking for the electric fan.

I have done the timing advance, just nobody seems to know why I can idle through city streets and be fine but on the highway when you have all of that cool air coming in it heats up. I dont know crap about the internals of the motor since I just bought the car and the motor was already built and the previous owner didnt know anything about it either.

Is the timing advancing enough for highway speeds (is it vacuum advance and working) also water pump may not be pumping at the rpms down the highway (make sure the pump is pumping in the right direction and not reveres). Do you have a air pocket (just take the thermostat out and drill two small 1/8 holes in it) and this will make sure you don't have a air pocket.

I agree with the above on tunning, timing and carb can realy heat things up. What does your plugs look like.

One thing to add to Skips post. At hiway speed no fan is needed. If the rest of your stuff is correct, of course.

Ya, I tried turning off the fans on the highway also, motor still went to extreme hot 230-240 before I pulled over and shut it down. This weekend I am going to drill the holes in the t-stat and make sure all of the air is out, if that doesnt work it is going to the shop.

Just a quick question, I have a serpentine pulley system and the crank pulley is a 6inch and the water pump pulley is a 4inch, could that be causing the overheating somehow?

Ya, I tried turning off the fans on the highway also, motor still went to extreme hot 230-240 before I pulled over and shut it down. This weekend I am going to drill the holes in the t-stat and make sure all of the air is out, if that doesn't work it is going to the shop. Most importantly is make sure the water pump is correct and flowing in the right direction. Take the cap off and start the car let it get up to temperature and look inside the radiator to see if it starts to flow, it may not flow until the T-stat starts to open, but if you drill the 2-holes then you should see some bubbling affect coming threw the cores of the radiator. Also leave about 1-2" lower then the top with fluid so it will give some room for expanding and contracting. This sounds like a FLOWING problem.

Just a quick question, I have a serpentine pulley system and the crank pulley is a 6inch and the water pump pulley is a 4inch, could that be causing the overheating somehow?The water pump pulley has a big factor in the revolution and flow of coolant, so yes but im not sure if thats an incorrect size for your setup. It very well is getting close to the issue and that is flow.

As mentioned, look at the belt direction of the w/pump pulley. If pulley is turning opposite from the crank pulley, it should be a reverse rotation pump. Or if the w/p pulley turns in the same direction as the crankshaft pulley, then a regular rotation pump is needed.

The w/pump pulley being a smaller diameter than the crankshaft pulley should help you, more flow, less heat.

Water wetter and antifreeze doesn't help much as antifreeze has a lower surface tension, aka, water sheets on the block, just like water on unwaxed paint, it sheets rather than beads up as with wax, this is why the water wetter didn't help.

Other reasons, higher rpms create more heat. A bored block has more heat due to thinner cylinder walls, heat conducts faster, less iron to absorb. Leaner fuel mixture creates more heat.

At a minumum, there should be a 20° difference between upper tank temp and lower tank outlet.Use a high flow thermostat, MRG-4684, 180°, I think on the part number, Mr gasket.

How fast is it getting there? Every once and a while after a long drive on the highway I'll get a small air pocket at the sensor which is at the back of my intake. The temp looks to go up fast but it's only air. You can verify your temps with a gun.

I figured I got about 10 miles down the highway before the car was at 240 and had me on the side of the road pouring antifreeze out of the overflow tube, luckly I had 2 gallons of water with me to cool things down then towed it home. Thanks for all your help guys trying to figure this out, I will be working on it this weekend to see what I can find.

I figured I got about 10 miles down the highway before the car was at 240 and had me on the side of the road pouring antifreeze out of the overflow tube, luckly I had 2 gallons of water with me to cool things down then towed it home. Thanks for all your help guys trying to figure this out, I will be working on it this weekend to see what I can find. Take out the T-stat and put it in a pot of water, with the wife meet thermometer check at what temp it starts to open. You will see little bubbles then fully open but pay close attention on when it opens and keep your eye on the thermomenter... It sounds like the T-stat and or water pump. Do like mentioned above with the water pump.

I would say your water pump is not flowing enough. What w.p. do you have? I'll guess and say it's a stock one.

Any updates Mark?

Well I drilled two 1/8 holes in the T-Stat and pulled the car up on to my steep driveway with motor running and cap off, WOW, bubbles everywhere, tons of air in that system, water is flowing nice now, no bubbles and drives down the road at 180, I feel stupid now but more educated. Thank you all for your help, you guys are awesome...

Well I drilled two 1/8 holes in the T-Stat and pulled the car up on to my steep driveway with motor running and cap off, WOW, bubbles everywhere, tons of air in that system, water is flowing nice now, no bubbles and drives down the road at 180, I feel stupid now but more educated. Thank you all for your help, you guys are awesome... You are the man, thank you for the up date.. Also very nice to hear:D.