Technical Rebuilt 324 olds overheating only on highway

So still working out kinks 1954 oldsmobile

324 w 371 Pistons and heads.

New radiator/cap/thermostat-all coolant system has been gone through and timing is a little farther advanced then spec. Have only been driving around in town and everything has been great (temp needle stays right in the middle after warmed up). Recently I got brave enough to start taking it on the highway. As soon as you get on it above 50 or so needle quickly rises to a little higher than 3/4 I have not pushed it too much past that. As soon as I get off the gas and coast it drops back down to normal.

Thoughts?


I welded in a new muffler and the stock exhaust is a little beat up and dented but no big kinks. The exhaust tip was completely flattened from being towed by a wrecker at some point and I straightened out the best I could. Could the exhaust be too restricting for the hopped up motor? You can kind of see the tip in this picture

 

Timing?
Radiator hose sucking together?
Using H2O or antifreeze?
Water pump new?

 

I would get a cheap temperature Guage at the parts store, that way you know what temperatures you are seeing.
When you say "overheating" is it puking coolant or just seems hot to you?

 

Buy an infrared gun-type thermometer and find how hot it's really getting. 3/4 up the gauge is no problem as long as it stays there.

 

My understanding is, if a car heats up at traffic lights, but cools off going down the road it is air flow. BUT, if the car runs cool at low speeds, or stopped, but heats up at speed, it is coolant flow.

At speed your motor is working harder and creating more heat. If the coolant isn't moving fast enough it could sit in the block and get hotter. I would check to make sure your pump is working well, as well as the radiator and hoses. Also, check the timing.

Don

 

is this a newly rebuilt or just recently swapped in motor? it is not uncommon for a newly rebuilt engine to run hotter than what is perceived to be normal until everything is seated. one thing to check and this happens frequently on an engine that has been apart is it gets air blocked. get it up to temp and crack open an heater hose purge some air out hope some of this helps Tom

 

New engine means you splurge on a new water pump, cheap insurance. New hoses, belts and of course thermostat.

 

It points to radiator possibly ... it may have plugged spots.

get it up to temp and feel the face of the radiator all over, looking for cooler spots.

324's run cool in my experience, and advancing does help on mine

 

F&J X2. Running hot at highway speeds is indicative of a radiator problem.

 

Yes freshly rebuilt engine with all new parts. And yes it's puking up coolant. I have shot it with a temp gun and got about 210 - ( that's shutting the car off at highway speed while moving and pulling over immediately. If I just pull over without killing the engine it cools down before I can pop the hood.

The lower hose does not have a spring but the system has so much pressure from the heat that when I press on it it pops the pressure release tab on the cap. I wouldn't think the hose would collapse under suction if everything was being pressurized.

Exhaust anyone?

 

i think you're wrong about thinking the lower hose won't collapse just because the system is pressurized.

 

3/4 ??? Start with a temp gauge with numbers on it.

 

X-2! There's a BIG diference between static pressure and dynamic pressure. Nobody said it yet, but are you sure that thermostat is opening all the way and (as in visually checked it on a stove), a d at the right temp? I seen more than one brand new (supposedly high quality thermostat that didn't open (or didn't open fully) right out of the box. Any kind of restriction to flow (such as this) and no spring in the lower hose will definitely suck that hose shut (assuming the pump is healthy). Can you run the car up to temp without a cap on it (without losing all the coolant), so you can check for flow? If your overheating at speed, you either don't have enough radiator (or coolant flow), or the air is somehow not going through the radiator core. Any gaps around the edges of the core, missing gravel pans, etc that might allow air a path of lesser resistance than through the radiator? Don't forget, air is a fluid (from a flow characteristic point of view) and will seek the path of least resistance. Also, a very cramped engine compartment can limit airflow by restricting the air that has already been through the radiator from leaving the engine compartment, creating a high pressure area behind the radiator that then limits flow through the core (granted, not likely in your scenario, but it happens all the time on late models, Corvettes, etc.). Point is, you need to think about the entire system, and all it's inputs (heat load, coolant makeup and flow, airflow, etc). Ignore the attached pic, I can't seem to delete it. Also, you swaped to bigger pistons, so I'm assuming you now have a larger cubic inch engine. Did you also add headers? Did you jet up the fuel system to match the new, larger sized engine? If it's lean, it's gonna run hotter, and the cooling systems not going to be able to band aid it.


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Also if you have 371 pistons in your 324, that is a serious over bore and tends to run a little warmer. I bet on your lower hose, It NEEDS a SPRING. Gary

 

Yes I know I have flow(but not how much). No headers- stock exhaust . Went up a few jet sizes. Might be a little lean but not by much. I thought it was weird that the lower hose didn't have wire but that's what the computer called for( they know best right...). I'll swap the hose and test the new thermostat and see what happens from there.

Thanks for the help.

 

I don't think any of the new hoses come with springs anymore.


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Hey, this is just a thought. My old Ply. slant six Valiant years ago had the same problem. Drove me crazy. Removed thermostat. No help. New one . No help. Even though fan belt looked good and was tight, I replaced it and solved the problem. Good luck.

 

Got to ask....

Do any of the V-8 heads have internal water distribution sheet metal tubes in them like some of the old inline engines have? I ask because I don't know and also because they corrode and mess up the water flow patterns.

That and maybe the T-Stat is in upside down?? and for sure the bottom hose without a spring in it will suck shut..

pdq67

 

Alright replaced lower hose. Took out thermostat and flushed everything even though it's all new. Coolant had some rust color to it and a slight oil slick on top(hoped it was just from greasing the hoses on install). I put one of those no spill funnels on top of the radiator to make sure there was no air. Well... If I rev the engine up real quick I keep getting a pretty big bubble just when i rev it. I did this for about 20 mins hoping it was just air in the system.

I started shooting everything with an infrared gun. Heads both running around 130(no thermostat) then noticed one of the exhaust ports was about 30 degrees cooler than all the others. Engine seems to not be missing but has a slight shake to it. Plug looks the same as all the rest. No white smoke at all from exhaust/ no milky oil.

This same cylinder is directly next to the temp sender.

I'm guessing blown head gasket. Not enough to allow coolant in but just enough when revving causes some exhaust gas to escape and cause a miss from low cylinder pressure. Heating up water next to temp sender. Therefore the increasing temp to the nearby guage at higher Rpms(highway speeds)

Darn.

This sound accurate?

 

I remember having a little trouble stabbing this head on and could have possibly damaged gasket on install but the thing ran great the first couple highway tests.

 

Rem ove the thermostat ,remove the upper hose from the radiator stick the water hose in block the upper inlet with a rag. Start the motor rev it up it should shoot water 5-6 feet. If the flow is low its the pump or the radiator. I have a nos spring if you need it.

 

do a leak down test on that cylinder and watch for air bubbles in the radiator fill neck.

 

One more theory...if your thermostat is sticking open, it could be that coolant can't stay in the radiator long enough to transfer heat at highway speeds....lower engine speed ( and thus slower coolant flow) around town would allow heat to be transferred out through the radiator as designed.

 

The theory of coolant not staying in the radiator long enough is an "Old Wives" tale. Defies the laws of Physics.

 

Then why does putting in a restricting washer help flatheads stay cooler in some cases ?
The physics as I see them, coolant flows through the motor removing heat, then through the radiator to dissipate heat through tubes and fins...if it flows through too fast, it will remove less heat from the block, and dissipate less heat through the radiator.

Have you ever heard the term "thermal runaway" ? It's often used in an electrical sense, but could be applied to the cooling system of a car as well.

I'm not trying to be an ass, please explain the fault in my theory using physics....

To the OP, I'd check to make sure you are using the proper sized pulley on your pump. It's a long shot, but if your pulley is undersized, and the pump is spinning faster than designed, it could add to the problem.

 

Not less heat. The coolant temp will not drop as much as it returns to the engine. But, there is more flow so the water coming out of the engine is not as hot. The engine produces 1000 BTUs of excess heat and the radiator sheds 1000 BTUs no matter the speed of the coolant. Unless the flow is so low that the coolant temp is raised above the boiling point before it gets to the Rad.

 

I understand the theory here, and in a perfect world, it makes sense. In the real world, I think there are too many variables in play, airflow, and ambient temperature to name a couple. What I'm suggesting may not be the OP's problem at all, but the fact remains, slowing the water flow down has helped cool a lot of engines better...and it's been well documented on this website.