Engine Runs Hot At Highway Speeds..!

[snahman]

Ok. I had to amend my other thread because there seems to be something different happening now. My 3.0 is running hot going at highway speeds "without" the a/c engaged..!....I previous thought it was just when I engaged the A/C, but today it proved me wrong. Even though it's 90 plus degrees here in NC, I'm running at 65 mph down the bypass thinking it would cool but when I got home, it was boiling out the radiator and overflow bucket..Any ideals..? Thanks..

 

[RonD]

You need to do a Glove Test to take cylinder to cooling system leak off the table, i.e. blown head gasket.

It is an easy, simple and FREE test
Cold engine
Remove rad cap
If coolant is at the very top drain some out, so it is about an inch down, lower is fine.

Remove Overflow hose, and plug that outlet on rad, use gum, putty, vacuum cap, ect.........

Find the Coil Pack(spark plug wires) unplug it's 4 wire connector, you want a no start

Get a latex glove and rubber band, or a balloon or even a condom
Put latex glove on rad cap opening, seal it using the rubber band.

Cooling system is now sealed, and a cold cooling system has no pressure and can generate no pressure, water pump just spins, it isn't a "pump"

Now crank the engine and watch the glove
If it starts to bounce then you have a leak from a cylinder into the cooling system.
A cylinder generates 150+ psi of pressure when starter motor is turning the engine, it's compression.

If glove just lays there no bouncing then all is well, move on to Radiator or water pump circulation problem.

If glove does bounce, remove 1 spark plug at a time and crank engine, when glove stops bouncing the last spark plug removed was from the leaking cylinder.

 

[snahman]

You need to do a Glove Test to take cylinder to cooling system leak off the table, i.e. blown head gasket.

It is an easy, simple and FREE test
Cold engine
Remove rad cap
If coolant is at the very top drain some out, so it is about an inch down, lower is fine.

Remove Overflow hose, and plug that outlet on rad, use gum, putty, vacuum cap, ect.........

Find the Coil Pack(spark plug wires) unplug it's 4 wire connector, you want a no start

Get a latex glove and rubber band, or a balloon or even a condom
Put latex glove on rad cap opening, seal it using the rubber band.

Cooling system is now sealed, and a cold cooling system has no pressure and can generate no pressure, water pump just spins, it isn't a "pump"

Now crank the engine and watch the glove
If it starts to bounce then you have a leak from a cylinder into the cooling system.
A cylinder generates 150+ psi of pressure when starter motor is turning the engine, it's compression.

If glove just lays there no bouncing then all is well, move on to Radiator or water pump circulation problem.

If glove does bounce, remove 1 spark plug at a time and crank engine, when glove stops bouncing the last spark plug removed was from the leaking cylinder.

Hello. .Thanks very much for this info..!.. I'll try and give this a whirl before the weekend is over and report back..!..

 

[RonD]

Your symptom points more towards a circulation issue, i.e. old water pump or clogged radiator, even a failing thermostat(not opening all the way)

But better to test for a cylinder leak first, because that is a black or white test, so no wasting of money, replacing cooling system parts when that isn't the problem.

 

[snahman]

Your symptom points more towards a circulation issue, i.e. old water pump or clogged radiator, even a failing thermostat(not opening all the way)

But better to test for a cylinder leak first, because that is a black or white test, so no wasting of money, replacing cooling system parts when that isn't the problem.

Thanks for your reply. I actually tested the system with a pressure tester today to see if it was leaking somewhere that I wasn't seeing. Found a leak coming out of my heater core pipes that after I've though about it, I've been seeing a small leak on ground sometimes but thought it was just coming off the body somewhere since it was further to rear of engine..!....I tightened the hoses and the tester held at the 13 lbs for over 30 minutes and never moved. I also tested the rad cap and though slowly, leaked down a little. I replaced it. Now..do you think this could have been the culprit..?..I haven't driven it far enough for it to run hot since it was getting dark.

 

[RonD]

It you have a cooling system pressure tester then do the "Glove test" using it.
Cold engine
Unplug coil pack's 4 wire connector for a No Start
Pump up cooling system pressure to 5-10psi, approx.
Crank engine and see if pressure increases, or starts to pulse up and down while engine is turning over.

A coolant leak wouldn't cause engine to overheat only at highway speeds, once you get low on coolant engine overheats at any speed.

 

[wildbill23c]

Ron, I tried your glove test on my 88 B2 works every time. No special expensive tools needed. Ruled out a blown head gasket within minutes. I was kind of afraid it may have one, but your test proved otherwise.

Another cause for overheating could be air in the system. An air bubble in the system could cause all sorts of overheating trouble...usually it happens even when parked, but is far quicker to happen while trying to drive the vehicle.

 

[snahman]

Ron, I tried your glove test on my 88 B2 works every time. No special expensive tools needed. Ruled out a blown head gasket within minutes. I was kind of afraid it may have one, but your test proved otherwise.

Another cause for overheating could be air in the system. An air bubble in the system could cause all sorts of overheating trouble...usually it happens even when parked, but is far quicker to happen while trying to drive the vehicle.

Couldn't an air bubble be introduced into a system via a leak ( ie in my case heater core hose.) Reason I ask because after I tightened the leaking hoses, replaced the slow leaking rad cap, I've driven the truck for a couple days and it hasn't ran hot as of yet..!.....Knocking on wood tho'...

 

[RonD]

Yes, a leak can suck air into the system as an engine cools down.

The overflow system on vehicles is pretty simple.
The radiator cap has TWO valves in it, a larger one that has a pressure rating and allows coolant to flow out of radiator into overflow tank and a smaller one that lets coolant flow back into the radiator as engine cools down.

When you heat a liquid it expands in volume, this is how a Pressure Cooker worked.
So as engine heats up so does the coolant, as it expands the pressure in the radiator will get up to 14psi(rad cap rating), at 14.1psi the radiator cap will be pushed open and hot coolant will flow to the overflow tank, then it will close again until pressure goes up above 14psi again.

After engine is shut off the coolant cools down, and shrinks back to its cold volume.
When pressure in Rad goes below 0psi, the smaller valve in the rad cap opens and coolant is sucked back in from the overflow tank.

So very simple operation.

If there is a leak in the engine/rad system then two things happen, you lose coolant of course, but when engine is cooling down the leak point can now also become a suction point to pull air into the system, instead of coolant from the overflow tank.
The air is much easier to suck in than a liquid(coolant).

So you get air in.

Easy way to check for that and if overflow system is working as it should is to remove rad cap before starting engine after it has completely cooled down, i.e. overnight, coolant should be at the very very top of rad, if system is working as it should.

 

[snahman]

Yes, a leak can suck air into the system as an engine cools down.

The overflow system on vehicles is pretty simple.
The radiator cap has TWO valves in it, a larger one that has a pressure rating and allows coolant to flow out of radiator into overflow tank and a smaller one that lets coolant flow back into the radiator as engine cools down.

When you heat a liquid it expands in volume, this is how a Pressure Cooker worked.
So as engine heats up so does the coolant, as it expands the pressure in the radiator will get up to 14psi(rad cap rating), at 14.1psi the radiator cap will be pushed open and hot coolant will flow to the overflow tank, then it will close again until pressure goes up above 14psi again.

After engine is shut off the coolant cools down, and shrinks back to its cold volume.
When pressure in Rad goes below 0psi, the smaller valve in the rad cap opens and coolant is sucked back in from the overflow tank.

So very simple operation.

If there is a leak in the engine/rad system then two things happen, you lose coolant of course, but when engine is cooling down the leak point can now also become a suction point to pull air into the system, instead of coolant from the overflow tank.
The air is much easier to suck in than a liquid(coolant).

So you get air in.

Easy way to check for that and if overflow system is working as it should is to remove rad cap before starting engine after it has completely cooled down, i.e. overnight, coolant should be at the very very top of rad, if system is working as it should.

Hey RonD. Thanks again for your reply. I have another question, not about this but something else.... Should I list it here or start another thread..?.. Maybe start another thread in case someone else may be experiencing the same problem..?

 

[RonD]

Different problem different thread is better, helps other when searching for a similar problem in the future, but this is your thread so up to you really