Hi temp reading but heater blows cold (1 Viewer)

[jaymar]

Short trip maybe five miles, scangauge says 230 degrees. Blast heat on high front and rear, vents blow cold. Temp slowly dropping while parked with heater on. (What else can I do to dump heat/lower temp in a hurry?)

Turn engine on and temp drops much faster, heat from vents. What the hell?

Possible explanations? Air bubble in system? Blocked heater core? Or…?

 

[Shipwreck]

Air in system.
Stuck/slow thermostat.
Head gasket.
Scanguage anxiety.

How's your coolant level?

 

[Saito]

Water pump take a sh*t ? ? Sounds like coolant may not be circulating ?

 

[jaymar]

Water pump aisin maybe 2yr old. Radiator leaky but I top up before going anywhere, distilled water. Came out of store 10 min later and temp had dropped 20 degrees. Engine was off. Not sure I believe that. I do have a HG issue, but temp always fine with rare exceptions. Other exception being a sudden spike to 137. Later heard gurgling under dash, thought must be air pocket. Hope that’s it. Scary. Thanks for checklist above.

More info. Got back in Cruiser with temp reading 166 after 20 minutes in store. Start driving, it's up 40 degrees to 206 in 90 seconds. Is that even possible, or does it have to be a false reading? Cranked the heat up, temp runs almost to 230 and goes up and down in the teens and twenties with no correlation to my foot on the pedal. Get home and park it, temp very slow to start down. Shut it off, same thing. Start it up, temp starts dropping, down to 198 in about two minutes. My current thinking is, these readings can't be accurate--on water, anyway.

Is there a good place the measure coolant temp with a contact thermometer?

 

[Malleus]

First thing: are you certain your heater valve works?

 

[Saito]

My set up isn’t stock any longer and the rear heat is deleted altogether. Does the heater valve control coolant to both front and rear ? If that’s good and your water pump is too, I’d say thermostat Even just putting your hand on the radiator and intake hose by the thermostat housing would be an indication of if it’s hot or not. Either way I’d say you’ve got a coolant flow issue. And 230° is pretty toasty.

 

[smritte]

EDIT

Misread what you posted. I agree with what the others said

 

[flintknapper]

Air pockets can make coolant temp readings swing wildly and very quickly.

Pull the Tstat altogether and button it back up. Make sure the system is full and properly 'burped'. Drive it and see what it does.

IF it still heats up we know it probably isn't Tstat related (although you can check while its out).

IF you don't have HG symptoms to point to....then I'd say you have air pockets.

Is your radiator cap recent and OEM?

Does your overflow tank show normal fluctuations and work properly?

 

[Marco Lau]

Air pockets. If you only drove 5 miles assuming not stop and go traffic, there is absolutely no way it will overheat with a 240 F readings. my rig will run out of gas wtih AC on and still reads south of 200F. You will know if your rig is truly overheating, AC cutoff. coolant dumping out of overflow, those are signs of your engine last attempt to shed excessive heat...

 

[jaymar]

First thing: are you certain your heater valve works?

Replaced the HCV 2015-16.

 

[jaymar]

My set up isn’t stock any longer and the rear heat is deleted altogether. Does the heater valve control coolant to both front and rear ? If that’s good and your water pump is too, I’d say thermostat Even just putting your hand on the radiator and intake hose by the thermostat housing would be an indication of if it’s hot or not. Either way I’d say you’ve got a coolant flow issue. And 230° is pretty toasty.

Never had an issue front or rear--except this time and one other, both associated with sudden apparent temp spikes to 230 and 237. Air in system could spike temp--could it also prevent heat reaching the vents?

 

[jaymar]

Air pockets can make coolant temp readings swing wildly and very quickly.

Pull the Tstat altogether and button it back up. Make sure the system is full and properly 'burped'. Drive it and see what it does.

IF it still heats up we know it probably isn't Tstat related (although you can check while its out).

IF you don't have HG symptoms to point to....then I'd say you have air pockets.

Is your radiator cap recent and OEM?

Does your overflow tank show normal fluctuations and work properly?

Can burp it but have radiator leak. Sometimes it needs nothing, sometimes half a gallon when I check before startup. This morning, it took a gallon. Cap is recent and OEM.

How will rad leak affect overflow tank function?

 

[jaymar]

Air pockets. If you only drove 5 miles assuming not stop and go traffic, there is absolutely no way it will overheat with a 240 F readings. my rig will run out of gas wtih AC on and still reads south of 200F. You will know if your rig is truly overheating, AC cutoff. coolant dumping out of overflow, those are signs of your engine last attempt to shed excessive heat...

Drove the same route today, low to mid 180s all the way. And higher ambient temp by 25 degrees or so. Bizarre. Overflow tank dry, but radiator leaks. Didn't think to try the A/C--which cuts off at what, 220 or so?

 

[Irish Reiver]

How will rad leak affect overflow tank function?

It will likely render the overflow tank, and it's functionality, useless. As the coolant heats up and pressurizes it will fill the overflow tank. When it cools down it will draw from the overflow tank. If you have a leak anywhere then the system will not pressurize correctly and coolant will vent through the leak. When the system cools it will draw air in to the system through the leak. You can usually spot this by noticing your overflow tank is at the correct level but coolant is low when you take the radiator cap off.
Number 1 priority is to fix the leak....

 

[bigredmachine]

Does the heater valve control coolant to both front and rear ?

no front only

 

[flintknapper]

It will likely render the overflow tank, and it's functionality, useless. As the coolant heats up and pressurizes it will fill the overflow tank. When it cools down it will draw from the overflow tank. If you have a leak anywhere then the system will not pressurize correctly and coolant will vent through the leak. When the system cools it will draw air in to the system through the leak. You can usually spot this by noticing your overflow tank is at the correct level but coolant is low when you take the radiator cap off.
Number 1 priority is to fix the leak....

^^^^

All of this. Spot on.

 

[jaymar]

It will likely render the overflow tank, and it's functionality, useless. As the coolant heats up and pressurizes it will fill the overflow tank. When it cools down it will draw from the overflow tank. If you have a leak anywhere then the system will not pressurize correctly and coolant will vent through the leak. When the system cools it will draw air in to the system through the leak. You can usually spot this by noticing your overflow tank is at the correct level but coolant is low when you take the radiator cap off.
Number 1 priority is to fix the leak....

Yeah, about that. New rad costs way too much to put that in until the HG issue is fixed, so...