Running Hot

[JerrySab]

Hey all,
My '88 2.9l auto is really not doing a great job cooling itself, which has me extremely nervous, given the history of these engines. Symptoms look like:

- Coolant temp gauge will level out right in middle of range pretty quickly, then creep and creep higher as driving continues.
- When shut off, after waiting a beat for pressure to ease, I pulled the cap off the radiator. Reservoir is full, coolant is hot. No oil in coolant. No bubbles or reaction from 'glove test'.
- While driving I hear a periodic sound that's sort of like a 'moaning' noise (lol), not quite a whine, more like a hum that comes and goes. is louder at low RPM but doesn't seem to change pitch when RPM goes up.
- I have new(er) 190 thermostat.
- PO says new water pump 4 yrs ago, but it may be crap?

I know this could be any number of things, I do suspect water pump, but if reservoir coolant is hot, then it must be circulating. engine fan is also spinning seemingly without issue.

Would love your thoughts.

 

[RonD]

Common sign of failing Fan clutch is that after warm up when driving say 40mph the temp gauge stays stable, but when you slow down or stop the temp starts to climb a bit

After engine has sat overnight open the hood and spin the fan, it should NOT spin, you can move it but not spin it
This is called Cold Lock for a Fan clutch
If it spins easily then replace fan clutch

Start engine
You should HEAR the fan grabbing air if its Cold Locked, then within 5 to 10 seconds the noise will lessen
After 30 seconds shut off the engine
Now you should be able to spin the fan easily, it fully unLocked

After driving for say 20-30min and radiator is fully warm up, shut off engine
Spin fan again, should be locked again, hard to spin, same as Cold Lock


Fan clutch has a bi-metal spring on the front and valves connected to the spring inside, and its filled with a light weight oil
When the oil is cold, i.e. sitting overnight, its thick so can't pass thru the valves very well so fan part is Cold Locked, hard to spin
As soon as you start engine fan blade resistance, being locked, warms up the oil fast, 5 seconds or so, and the oil can now flow thru the valves and fan is now unlocked
As the Radiators CENTER part heats up it warms up the bi-metal spring on the front of fan clutch, as the spring expands from the heat it starts to close the valves, which starts to lock the fan blades to Water Pump RPMs, the warmer if gets the closer to water pump RPMs the fan spins and the more air it pulls thru radiator and into engine bay
If CENTER of radiator gets clogged up the fan clutch operation is diminished, spring is not heated enough
After radiator is warmed up pull back the shroud and run you hand across the fins, should be evenly warm but warmer nearer the upper rad hose and get a bit cooler towards the lower rad hose
You WILL feel cold spots, and thats where passages are blocked

Clogged radiator will, of course, cause what you describe


Clogged heater core can cause temp to go up and down
Unhook the two heater hoses at the fire wall and flush heater core in both directions with garden hose, you won't loose much coolant
You should REVERSE heater hoses at the firewall every 2 years when you change coolant, this helps heater cores to last longer by reversing the flow thru them
Heater cores do not have a set IN and OUT

 

[JerrySab]

@RonD do you accept payment in cases of beer?

 

[JerrySab]

Tying bow around this one,
Radiator had SO MUCH clay in it. I ended up just replacing it, which was mostly easy. Failed to notice the new rad being 1.5" thicker than the previous, so fan shroud kept catching on harmonic balancer.
Also, previous owner bypassed heater core, because ( I learned) it was leaking like a sieve. I wanted heart back, so replaced that also. HEATER CORE ALSO .5" LARGER ALL AROUND WTF PEOPLE.

This truck is running SO COOL. none of the creeping temp issues remain. in fact, I think with fan shroud closer to block, it runs almost too cool. Not sure if that's a thing with a 2.9, so I'll take it.

Ok. A NEW QUESTION, I was burping the system after slapping it all back together. and noticed, when I would tap gas pedal, I'd see bubbles in the funnel. Like, almost right away. I don't believe it's a head gasket issue. Because my guess, is that the bubbles would be at least slightly delayed. I do have new beefy heads. My thought, was perhaps the spill proof funnel wasn't super air tight, and then the higher rpm > quicker water flow would create suction stronger than the funnel seal could block. But I'm also concerned about the water pump. Like, the clogged radiator was straining the pump or bearings, and there's an air leak somewhere there.

 

[RonD]

Cold engine
Pull heater hose off at firewall, the one that goes to/near thermostat housing is best, but either works
This allows an exit for air from both heads while filling
Refill at radiator
When water/coolant starts to flow from hose end and heater core all the air on thermostat side of cooling system is gone, reconnect hose

Also swap around heater hoses at firewall every 2 years when you change coolant, or sooner
This reverses the flow thru heater core keeping it cleaner and it will last longer

Bubbles in coolant is not a good sign

 

[rusty ol ranger]

It depends on the bubbles....
Sometimes the vacuum created by the waterpump pushing coolant by the open radiator neck can cause bubbles.

But if its like....blowing bubbles...yeah not good

 

[JerrySab]

Thanks for this. Obviously hoping its water pump vacuum related. It's not overheating, nor is it losing coolant. Oil is clear. Coolant looks clean as it's circulating. There's no exhaust smell in the bubbles. Still, if air is seeping into the coolant system, I know it'll cause problems. I'm just not quite sure where to start searching.

Is the overflow reservoir meant to be sealed? if the hose running from overflow res to radiator is worn out or poorly fitting, could bubbles originate there?

 

[alwaysFlOoReD]

Would the glove test help determine where the bubbles are coming from?

 

[rusty ol ranger]

Thanks for this. Obviously hoping its water pump vacuum related. It's not overheating, nor is it losing coolant. Oil is clear. Coolant looks clean as it's circulating. There's no exhaust smell in the bubbles. Still, if air is seeping into the coolant system, I know it'll cause problems. I'm just not quite sure where to start searching.

Is the overflow reservoir meant to be sealed? if the hose running from overflow res to radiator is worn out or poorly fitting, could bubbles originate there?

Im not sure on the coolant bottle...but i dont think it being not sealed well would cause it.

Personally id run it...just keep a damn close eye on the oil and temp for a few weeks, as well as coolant level.

Would the glove test help determine where the bubbles are coming from?

Its possible...if its blowing compression into the radiator it would inflate it, but if its water pump vaccum it would pry suck it the other direction...id think.

 

[RobbieD]

Is the overflow reservoir meant to be sealed? if the hose running from overflow res to radiator is worn out or poorly fitting, could bubbles originate there?

The overflow hose from the radiator neck to the reservoir has to fit tight and be sealed on both ends, especially at the radiator neck. If it's loose, coolant will go out into the reservoir when the engine is warm, but after it cools off the loose hose will suck air back into the cooling system instead of coolant.

A new overflow hose and a couple of spring clamps would be cheap, and worth the trouble.

 

[JerrySab]

@RobbieD GREAT. starting here.

 

[RonD]

Overflow tank is vented, not sealed

Rad cap is rated at 14-16psi but there are two valves in rad cap

As engine/coolant warms up coolant EXPANDS in volume, 1gal becomes 1.5gal, that's where the pressure in the cooling system comes from
When it reaches 14psi at the rad cap, the rad cap's larger valve is pushed open and hot coolant can flow from rad cap port to the BOTTOM of the overflow tank
When you shut off the engine coolant cools down and SHRINKS in volume
If any coolant flowed out to overflow tank then pressure in the radiator/engine will drop to -1psi, negative pressure, this will suck open the smaller center valve in rad cap and SUCK coolant back in from the BOTTOM of the overflow tank
Simple system if everything is working

Overflow hose needs to be air tight
Overflow tank needs to be clean, flush it out

System is self purging of air
If there was air in the cooling system it would collect at the top of the radiator
When engine/coolant is heated up and the rad cap opens(14psi) the AIR is sent over first to BOTTOM of overflow tank where it bubbles up and is gone
When engine cools down COOLANT is sucked back in replacing the air

If you drive it a few days then after is cold, open rad cap, should be full to the top, NO AIR
If there is air then you have a coolant leak in the rad/engine, or in the overflow hose
Air is easier to suck in than coolant

None of the above would cause air bubbles in circulating coolant

 

[JerrySab]

None of the above would cause air bubbles in circulating coolant

well, crap.

 

[RobbieD]

I would just run it and keep an eye on it.

You've put a new, thicker radiator in it, and it's now running cooler. It sounds like your temp gage is working. Just keep checking the radiator level and the overflow tank often, and monitor the temp gage whenever you're driving it.

If it stabilizes and doesn't need lost coolant replaced, and if it runs cool, you're good. If there's something else going on that needs to be looked into, it'll become apparent.

As long as you don't let it overheat, driving it won't hurt it.

If it's an auto trans, you do have a supplemental cooler for the ATF, right? (a separate cooler behind the grille)

 

[JerrySab]

Much appreciated @RobbieD