overheat only over 3000 rpm

-
D

diehard polylover

Member
Joined
Oct 9, 2024
Messages
14
Reaction score
17
Location
South Spain
I am writing here as I hope to find a hint to solve this particular overheating problem:

I got a stock 318 poly engine with the "power pak" option, perfectly tuned and performing. The radiator has brass top and bottom tanks with modern three lawyer cores; it was cleaned by a professional shop ( dismantling the top and bottom tanks and passing a rod in the vertical core passages) to make sure the cores were free and flowing. I use a specific red liquid for radiators. The rad has the proper rubber fittings to avoid the loss of airstream from between its top and the front frame. 13 pounds radiator cap.

So.... It doesn't overheat when I drive around at 1500-2000 rpm, but if I hit the highway, as soon as I get over 3000 rpm it starts to overheat. (the max rpm of the engine is 4400) and if I insist, no matter the four running fans installed on the front of the core and running like hell, (pushing in the right direction) the engine slowly get to the boiling temperature. 230°F.

I imagined that maybe the limestone accumulated in the decades in the inside of the block might act as heat insulator, thereby keeping the liquid from cooling the engine.... therefore I did one hell of a cleaning, making it run with salty water for several days first it (it dissolves the limestone) , then with a mixture of water and baking soda after, (to take the acidity of the salt out of the block), then washing and rewashing tens of times the engine making it run with running water in the radiator (with a hose) while the return hose was detached and discharged the return water in a container.... until tasting the water coming out of the radiator it was clean and almost drinkable. (almost) Then I replaced the water with the proper coolant, and....
the overheating just got a little further up on the rpm. But it is still there. I can't drive at a steady 3500 - 4000 on the highway without overheating.

Any hint?
Please....
 
Lower rad hose sucking flat? That is...Is there a metal spring in the lower hose to prevent collapse?
 
Uhh, you have 4 pusher fans in front of the radiator?

I know you've broken this down into RPM, but I assume that this "overheats over 3k RPM" probably translates directly to a highway speed as well. As in, it doesn't overheat at 3,000 rpm in 2nd gear at lower speeds, but only at 3,000 RPM out on the highway at whatever speed that translates to?

Overheating out on the highway is usually an airflow issue. And if you have 4 pusher fans, well, they're blocking your airflow.

What is the combined CFM of all your fans?
 
Murray said:
Shroud?
Click to expand...

Shouldn’t matter in this instance, for several reasons

-pusher fans on the front can’t have a shroud

-lack of a shroud with a mechanical fan will hurt low speed cooling, not highway speed cooling

-a factory shroud won’t be blocking enough air flow to have an air stack problem at highway speeds

The only scenario I could see that would contribute to the over 3k rpm, highway overheating would be one of those flat, cookie sheet style aftermarket shrouds with an electric fan. But that would mean he’s running pushers and pullers, which would be a whole different can of worms
 
how about a slipping water pump impeller?
 
Lose the electric fans, I would go with the stock arrangement. Check into the lower hose collapsing.
 
diehard polylover said:
therefore I did one hell of a cleaning, making it run with salty water for several days first it (it dissolves the limestone) , then with a mixture of water and baking soda after, (to take the acidity of the salt out of the block),
Click to expand...
Salt water is basic, lime is basic.

You need to use a proper cooling system cleaner to dissolve any mineral buildup.

Timing will effect highspeed engine temp.

Water pump speed will effect high speed engine temp.

Automatic trans can effect engine temp


If you were in the driveway at 3000 rpm will the temp rise as described?
 
From memory, those cars came with a 4 blade mech fan.

I would get rid of the 4 elec fans. They are probably blocking airflow at higher road speeds.
 
72bluNblu said:
Overheating out on the highway is usually an airflow issue.
Click to expand...

No, if it's a flow issue of any kind, it's usually a waterflow issue, because at highway speeds there's usually plenty of airflow through the rad by the forward motion of the car. But yeah, maybe not if the rad is blocked by seventeen fans, or four of them.

(Overheating at idle/low speed/stuck in traffic, now that's usually an airflow issue due to insufficient fan.)
 
CFD244 said:
Lower rad hose sucking flat? That is...Is there a metal spring in the lower hose to prevent collapse?
Click to expand...

'Collapsed rad hose' is largely a myth. The upper hose would never collapse, and the only reason why the lower hose could collapse is if there is severe clogging or restriction in the radiator or thermostat—and the hose would then un-collapse once the system heats up and builds pressure.

I don't claim it can't happen—only that it is exceedingly rare and has one specific cause. Think it over: that bottom hose runs from the radiator outlet to the water pump inlet. The only way for there to be negative pressure in that hose is for there to be extreme restriction upstream of that hose so the water pump pulls a vacuum, and the hose would have to be weak/soft, and there'd have to be no/low pressure in the system as a whole.

That spring that used to come in some rad hoses was meant to keep the hose from kinking if overbent. Cut the hose to length (as required) and install it properly, and have good engine mounts, and there won't be any kinky stuff happening.
 
slantsixdan said:
No, if it's a flow issue of any kind, it's usually a waterflow issue, because at highway speeds there's usually plenty of airflow through the rad by the forward motion of the car
Click to expand...
That's the point that at highway speeds there should be sufficient air flow to cool.

BUT...

if the air flow is restricted for some reason -fans in the way, shroud, massive leaky air seals, blocked fins - then there WOULD be an airflow issue.
 
slantsixdan said:
'Collapsed rad hose' is largely a myth. The upper hose would never collapse, and the only reason why the lower hose could collapse is if there is severe clogging or restriction in the radiator or thermostat—and the hose would then un-collapse once the system heats up and builds pressure.

I don't claim it can't happen—only that it is exceedingly rare and has one specific cause. Think it over: that bottom hose runs from the radiator outlet to the water pump inlet. The only way for there to be negative pressure in that hose is for there to be extreme restriction upstream of that hose so the water pump pulls a vacuum, and the hose would have to be weak/soft, and there'd have to be no/low pressure in the system as a whole.

That spring that used to come in some rad hoses was meant to keep the hose from kinking if overbent. Cut the hose to length (as required) and install it properly, and have good engine mounts, and there won't be any kinky stuff happening.
Click to expand...
Oh. Ok. An engine builder friend told me they chased an overheat problem down to a collapsed lower hose....Just passing it along. :)
 
Dana67Dart said:
slantsixdan said:
No, if it's a flow issue of any kind, it's usually a waterflow issue, because at highway speeds there's usually plenty of airflow through the rad by the forward motion of the car
Click to expand...
That's the point that at highway speeds there should be sufficient air flow to cool.

BUT...

if the air flow is restricted for some reason -fans in the way, shroud, massive leaky air seals, blocked fins - then there WOULD be an airflow issue.
Click to expand...

Yes, which is why my whole comment was:

No, if it's a flow issue of any kind, it's usually a waterflow issue, because at highway speeds there's usually plenty of airflow through the rad by the forward motion of the car. But yeah, maybe not if the rad is blocked by seventeen fans, or four of them.
 
thanks for the replies, friends.

No, the 4 fans are BEHIND the radiator. I took the stock four blade fan off. The car was overheatig since its beginning, especially in stop and go traffic, that's why I went with the four fans and thermal switch, and for city traffic they work very well.

I put a double temperature thermal switch at the bottom of the radiator which activates first the TWO TOP fans at a temperatire of 180 °F and then activates the other TWO LOWER fans at the temperature of 190 °F. Thereafter I have four fans sucking air through the radiator.

I am a fanatic of engine tuning, so I tune the engine by hear, which in my opinion is the best way to do it, as the stock timing position might not be the best compared to the **** gasoline they sell today.
Of course I keep the carb at its top tune as well.
It's a weekly check all my life with this car.

Actually In the normal traffic condition the two LOWER fans seldom are activated. Besides, if driving at moderate speed on a country road even the two TOP fans switch off as the temp stays a tad below 180.

I did note some improvement after the crazy cleaning, it seems the temperature stays cooler, But I haven't had the chance to hit the highway on a hot day, as the weather here is not as hot as last month. I'll take the chance as soon as I can.
I'll keep this post updated.
 
Are you running vacuum advance? If you are not, you need to be.

If it was overheating prior to the electric fans then my best guess is the pump isn’t turning fast enough.

I always suggest a Stewart Component high flow thermostat. And a high flow water pump.

But none of that stuff does any good if the pump is turning too slow.

If I understand you correctly you are saying it’s getting hot now at a cruise. That can easily be tuning.

If prior to that it was getting hot at idle and in traffic that’s a different issue.

It sounds like you have multiple issues going on.
 
If it was over heating before all the modifications with all of the stock equipment, then, instead of throwing money and parts at the thing, you need to use actual DIAGNOSIS. Try it. It works.
 
once you are at about 30+ mph, the fans are not accomplishing anything except potentially slowing down the air flow through the radiator. So better more powerful fans will not solve your problem. look to one of these other suggestions as a solution.

4 fans is a lot of fans to fit on a Mopar radiator core. Can I ask what size they are? If they are less than 12" each, they are extremely inefficient and you'd do much better with 2 12" fans or go back to mechanical fan and shroud setup. Again, this advice is for speeds under 30mph and the idea that you will have less blockage for higher speed driving.

Finally, It would be nice to find the exact reason for the 3000rpm issue but It could be that the heat generated by the 3000 rpm's is just too much for the volume of fluid you have in your system. A larger radiator with more volume could solve some hidden issue if you start running out of other solutions.
 
diehard polylover said:
I am a fanatic of engine tuning, so I tune the engine by hear, which in my opinion is the best way to do it, as the stock timing position might not be the best compared to the **** gasoline they sell today.
Click to expand...
Perhaps this is part of the problem…I’d be interested to know where initial timing is set.
 
Newbomb Turk said:
Are you running vacuum advance? If you are not, you need to be.

If it was overheating prior to the electric fans then my best guess is the pump isn’t turning fast enough.

I always suggest a Stewart Component high flow thermostat. And a high flow water pump.

But none of that stuff does any good if the pump is turning too slow.

If I understand you correctly you are saying it’s getting hot now at a cruise. That can easily be tuning.

If prior to that it was getting hot at idle and in traffic that’s a different issue.

It sounds like you have multiple issues going on.
Click to expand...
Thanks for your kind reply.

1) yes of course I have the vacuum advance. the correct one for the power pak, which is 13 degree advance. It works very well.

2) A high flow thermostat will be my next move for sure.

3) I have the feeling that for a 318 A poly there isn't any choice of water pumps.

4) When taking off the return hose from the engine, The flow of the water just slightly off idle is really abundant.

5) as I wrote earlier, after all the cleaning I did , I still have to check the behaviour on the highway,

6) Hot in traffic is a thing of the past now with the 4 fans setup.

I have the feeling that I am close to the solution, as I discovered that the coolant feed hose was squeezed in one of its bends before the pump and maybe didn't let the full flow of the coolant to get to the pump ....
The reason for that is because it was a little longer than the stock one, therefore at the very back of it there was a sharp bend reducing the flow.!

and no, I haven't got a spring in the hose..... I neve r had it.....
 
The interesting thing about the lower hose sucking shut, - is that as soon as you let the rpms drops from the revs nec to suck it closed, it will immediately open , and stay open till next time revved, then shut.
Cruise at 60 mph, it gets hot, pull over, idle, open hood, inspect for problem, hose is open .
Ask me how I know.
 
You must log in or register to reply here.
-

Back
Top