Slant Six overheat at cruise speed, especially going uphill

-
1966DartConvertible

1966DartConvertible

Well-Known Member
Joined
Aug 5, 2010
Messages
516
Reaction score
21
Location
Malaysia
Hi

It was about 90F today and took the Dart for a trip outta town. After about 25miles of driving the temp started climbing, first to about 2/3 then when it reached 3/4 mark while on a hilly section, i stopped at a rest area and let it cool down.

What can cause this? Ignition timing not set properly?

I understand if its overheating while stuck in traffic but going 70mph on the highway?

Would radiator shroud help?

Thanks

Syed
 
I would say a plugged cooling system (make sure water is actually flowing through the radiator by pulling off the cap while its running only when it's cold. Could also be a stuck thermostat (try putting a 180 in), or a bad water pump, or worst case scenario the water jackets are all plugged up. Shroud will help but like you noted, only while sitting still. Best of luck, Dan
 
plugged cooling for sure. T stat, gummed up Radiator, Something like that. There is no reason for this if you cooling system is working properly. Also make sure you have a good mix of coolant to water.
 
hemitheus said:
plugged cooling for sure. T stat, gummed up Radiator, Something like that. There is no reason for this if you cooling system is working properly. Also make sure you have a good mix of coolant to water.
Click to expand...

They dont have parts store here that sells Mopar Parts... all need to order from good ol' Ebay...

Would it be ok to take out the thermostat for now, and run it like that until new thermostat arrive in a couple of weeks? Ambient temp here is constantly above 90F so even without a thermostat, engine temp should come up to operating temp very fast.

I know this is bad practice, but ... better than a overheated engine I suppose?

Thanks again.

Syed
 
I chased this problem in a 62 Impala I had and it turned out that the rad needed reaming out but it was so old and brittle I just got another one. Inside the top of the rad looked fine but it was plugged big time
 
could easily be ignition timing. what are you set at? make sure your advance is working properly. to check the mechanical, hook up your timing light normaly (vac advance disconected) then slowly rev the engine, you should be able to watch the timing mark move away from TDC. to check the vac advance remove the dizzy cap (engine off) and apply vacume with a pump, you should be able to see the plate move as you increase vacume.
 
Re-core/replace radiator and replace thermostat i had the same problem
run cool in traffic overheat on interstate my radiator was 70% plugged
 
It's a flow problem for sure as everyone else noted.
Due to lack of available parts in your area, you can try this without having to buy anything (Yet anyway)
Disconnect your radiator hoses (The top one pull from the engine and the bottom one from the radiator)

Pull the thermostat housing and point the lower hose at the ground as not to blow crap all over your engine compartment.
Put a water hose AND and compressed air nozzle both into the manifold where the thermostat went and wrap them both with a towel or rag to make as good of a seal as possible.
Turn the water on as high as it can and about every 3-5 seconds hit it with the air while holding the towel down tight on the intake.
The water will get blasted through the engine block backwards from the normal flow direction and you might be suprized how much crap comes out of the block.

Next do the radiator the exact same way at the bottom hose flange and blow it out the top hose.
This will "Backflush" the radiator.

No cost at all, just some of your time and may be well worth it.
 
feel the radiator after your up to temp. If there are colder spots, your gummed up. A rod out is still an option even in your neck of the jungle.

got pools in Malaysia? Try this pool acid procedure on some dirt lot, itll etch concrete and kill grass...
"...For about $1 worth of solution, you can clean it as well as any radiator shop, especially since you will have to remove it anyway, unless you want to pay a highly trained radiator "technician" and add that to the bill.

The radiator flush article in Toyota Trails, as referenced above, was written by Mark Whatley and is on page 25 of the July/August 1998 issue. To summarize:
..remove the radiator or heater core
..empty the remaining coolant
..position the openings facing up and fill with muriatic acid. Let it sit for 10 - 15 minutes--no more
..flush with clean water, and repeat the procedure.
..flush thoroughly with clean water, and re-install

Three things: this procedure is designed for old-fashioned, brass radiators. Never use on the new-style aluminum/plastic coolers. Do not use the acid wash with the radiator in the vehicle--it will inevitably spill on surrounding parts and damage them. Finally, don't spill this mess on your driveway. It will eat concrete...."


I would add a baking soda water final rinse to neutralize any residual acid. Works on heater cores too. CLR is also good, but more expensive.
 
dusterdan said:
I would say a plugged cooling system (make sure water is actually flowing through the radiator by pulling off the cap while its running only when it's cold. Could also be a stuck thermostat (try putting a 180 in), or a bad water pump, or worst case scenario the water jackets are all plugged up. Shroud will help but like you noted, only while sitting still. Best of luck, Dan
Click to expand...

Ok First step first...

Its not the thermostat (opens fine in hot boiling water)

Before
183.jpg


After
182.jpg


Tomorrow I will try flushing the cooling system and fill up with new coolant/water mix and see how it goes.

Syed
 
There is enough snot/scum/slime on that thermostat to tell me things are filthy in your cooling system.

If you plan to flush it out, drain the coolant & flush it with clear water. The drain it again & fill it with water and 16 ounces of Simple Green or Zep Orange, and if that is not available down there use a good commercial floor stripper like you would remove wax with.

Close the system up without the thermostat, and drive it for about 10 miles. Make sure you get the engine speed above 3000 a few times.

Then go drain the filth out.

.
 
bohica2xo said:
There is enough snot/scum/slime on that thermostat to tell me things are filthy in your cooling system.

If you plan to flush it out, drain the coolant & flush it with clear water. The drain it again & fill it with water and 16 ounces of Simple Green or Zep Orange, and if that is not available down there use a good commercial floor stripper like you would remove wax with.

Close the system up without the thermostat, and drive it for about 10 miles. Make sure you get the engine speed above 3000 a few times.

Then go drain the filth out.

.
Click to expand...

Quick question:

Before i start flushing, i better get this right.

The water flows from the water pump into the lower rad hose and up thru the core and out at the top of the radiator and eventually entering the block thru the thermostat housing, right?

If so, to reverse-flush, I need to blow water FROM the TOP and out at the BOTTOM of the radiator?

Thanks

Syed
 
Before you reverse flush, you need to get the bottom tank cleaned out.

Reverse flushing a system full of crud can drive that crud into the radiator tubes.

Run the system with the thermostat removed while running a cleaning agent in the system. Then pull the lower radiator hose off, and flush it from the top to get the lower tank clean first. It is the lowest point in the system.

.
 
Not if you separate them by disconecting the hoses
and flush both ways through the radiator a couple of times.
If theres not enough flow to cool the car and he does what I said, then in the very least case he didn't have to spend any cash or order possibly pointless parts to pinpoint the problem area.
 
That stat didnt look half bad to me, pulled rusty ones that still worked fine and the coolant was mud. Is your distributor hooked up to ported vacuum? Is it still holding a vacuum?
(pop the cap, take the hose off the carb and apply vacuum to see if the breaker plate . If not, check vacuum pot and lube plate) Are you getting any knocking or pinging up hills?
 
I know this sounds stupid but are the rad hoses really old...... are they collapsing?
 
I would bet on the plugged radiator myself but before you do ANYTHING, check to be sure the fan is on the correct way and not backwards. I know, you'll all laugh but you'd be surprised how many times I've seen that. At high RPM on the freeway, the air just won't flow through. The fan is trying to push the air forward at the same time the ram air coming through the grille is trying to flow to the rear.
 
HemiMark said:
I know this sounds stupid but are the rad hoses really old...... are they collapsing?
Click to expand...
What Mark said. The lower hose can collapse at speed. (It gets sucked shut.)

A stuck thermostat would overheat it at any speed.

A shroud only helps at low speed. It directs the air through the rad.

If the radiator is old, that's most likely the culprit.
 
I agree with the lack of flow theories here. It could be rust sludge in the water jackets or rust chips clogging up the small passages going up into the head, through the head gasket. Also could be the radiator passages need to be "rodded out" or just have it rebuilt. I believe I've heard people mention that cheap thermostats down flow enough when open because the hole isn't big enough.....but that's usually in a performance V8 though.
 
Sorted! Flushed the system today. Top-up with coolant and so far so good. And Yes a lot of brown colored rust cAme out from both Rad n Engine..
 
You must log in or register to reply here.
-

Back
Top