Intermittent Heat

[smythcounty]

After driving the vehicle for a while the heat turns lukewarm to cool. If I stop or turn off the heat for a few minutes it may turn hot again but not always. Usually at idle it is hot but not always.

What I’ve competed thus far:

1) Bypassed heater control valve and plumbed heater core straight
2) Flushed heater core with CLR (water ran smoothly through) and radiator twice
3) Replaced thermostat twice

Any other suggestions would be greatly appreciated.

Thanks

99 Ranger XLT
Extended Cab
AT
4.0L

 

[bobbywalter]

Is the belt routed correctly? Looks like verified install of stat in other thread

 

[DILLARD000]

ThermoStat Make+Model+TempRating?

 

[smythcounty]

ThermoStat Make+Model+TempRating?

First one was carquest premium 192
Second one motorad ultrastat 198

 

[smythcounty]

Is the belt routed correctly? Looks like verified install of stat in other thread

Yes I confirmed the belt routing this morning.
I installed the thermostat with the long end going into the block.

 

[bobbywalter]

Head gasket or waterpump/ timing cover gasket...in wrong .... Or simply blend door malfunction.

The heater core can be swollen and flow well but not transfer heat well... I went through that with a ho pump on my v8, I would swap then core every winter. But it's a 10 min job in a gen 1

Overheating after t stat install and hose sucking shut as reported before kind of takes the core as lower priority.

Has it had head gasket work or sealer poured in it? Did you manually close the ac divider so it only pulls cab air and pushes through the heater core?

 

[sgtsandman]

How’s the engine temp been? Is it staying constant once it reaches operating temp? I’m wondering if the water pump isn’t moving enough coolant. Like the impeller isn’t holding tight to the pulley shaft or the impeller has corroded away.

 

[smythcounty]

Head gasket or waterpump/ timing cover gasket...in wrong .... Or simply blend door malfunction.

The heater core can be swollen and flow well but not transfer heat well... I went through that with a ho pump on my v8, I would swap then core every winter. But it's a 10 min job in a gen 1

Overheating after t stat install and hose sucking shut as reported before kind of takes the core as lower priority.

Has it had head gasket work or sealer poured in it? Did you manually close the ac divider so it only pulls cab air and pushes through the heater core?

After changing to the second thermostat the overheating issue and hose sucking went away. I believe I was sold the wrong thermostat.
No headgasket work or sealer.
Not sure what you mean by manually close the AC divider, is that the blend door?

 

[smythcounty]

How’s the engine temp been? Is it staying constant once it reaches operating temp? I’m wondering if the water pump isn’t moving enough coolant. Like the impeller isn’t holding tight to the pulley shaft or the impeller has corroded away.

I tested last night while driving with my scanner and it fluctuates between 192 and 203.

 

[bobbywalter]

Yes .. the blend door.

You know it's pumping steady coolant through the bypass loop....well I assume you have a flush tee and elevated and observed it at this point.

So the system doors ..depending on year and model have electric, mechanical and vacuum parts over the generations...I don't recall specifics.

It may be easier to run clear hose to the core to verify flow temporarily...

But I would verify blend door scenario in your loop of travel.

 

[RonD]

Unfortunately it reads like heater core is partially blocked, it can still have good flow just not through the whole core

So fan on high cools it down and coolant can't warm it back up fast enough because the whole core is not getting hot
Stopping the air flow lets the core heat back up again

After engine is warmed up put temp to Hot and fan on High
Open hood and feel the two heater hoses at firewall
One will be hot(coming from engine)
Other should be much cooler(return to water pump)
If there is not much of a temp difference then heater core is not getting full circulation

Heater core is not a forced flow pathway, so it can't be blocked completely causing a hose to blow off
Which is why it can still have good flow while partially blocked
Clean core tubes just have less resistance to flow than the bypass at the top of core, so coolant tends to flow thru open tubes keeping them hot
As tubes get blocked they get cold of course but flow doesn't decrease thru the core because of the internal by-pass

Just as a heads up
You should reverse the heater hoses at the firewall on ANY vehicle every 2 years or so to reverse the flow thru the core, this will help keep it cleaner and last longer
Coolant has anti-corrosion chemicals, but they can only protect what they touch, when tubes get blocked by debris or ???, then flow stops and corrosion gets worse in that area

 

[bobbywalter]

Unfortunately it reads like heater core is partially blocked, it can still have good flow just not through the whole core

So fan on high cools it down and coolant can't warm it back up fast enough because the whole core is not getting hot
Stopping the air flow lets the core heat back up again

After engine is warmed up put temp to Hot and fan on High
Open hood and feel the two heater hoses at firewall
One will be hot(coming from engine)
Other should be much cooler(return to water pump)
If there is not much of a temp difference then heater core is not getting full circulation

Heater core is not a forced flow pathway, so it can't be blocked completely causing a hose to blow off
Which is why it can still have good flow while partially blocked
Clean core tubes just have less resistance to flow than the bypass at the top of core, so coolant tends to flow thru open tubes keeping them hot
As tubes get blocked they get cold of course but flow doesn't decrease thru the core because of the internal by-pass

Just as a heads up
You should reverse the heater hoses at the firewall on ANY vehicle every 2 years or so to reverse the flow thru the core, this will help keep it cleaner and last longer
Coolant has anti-corrosion chemicals, but they can only protect what they touch, when tubes get blocked by debris or ???, then flow stops and corrosion gets worse in that area

My first suspicion.

The heater core can be swollen and flow well but not transfer heat well... I went through that with a ho pump on my v8, I would swap then core every winter. But it's a 10 min job in a gen 1

Overheating after t stat install and hose sucking shut as reported before kind of takes the core as lower priority.

My first suspicion when he very first posted in the other thread Ron.....

it could have froze at one point that can swell them as well causing heat transfer issues.


Pulling the dash is intimidating to the uninitiated....And was the next step ..

But after a few minutes of checks in flow...I would have pulled the core just to physically verify it ..you can weigh it and know your screwed ..... depending on actual model...modified the system for future core replacement ease. The later trucks are not friendly ..but it can be done under 2 hrs.

And aftermarket heater cores suck.