No heat at highway speeds...
November 16th, 2019, 08:25 AM
#1
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No heat at highway speeds...
My heater was not working so we replaced the heater control valve and works great.....But when im driving 50mph or higher, it starts blowing cool air....It's acting like the heater control valve is loosing it's vacuum thus closing the valve... Any ideas????
November 16th, 2019, 10:04 AM
#3
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Do you have the vacuum reservoir hooked up correctly, and is the check valve connected properly?
November 17th, 2019, 06:21 AM
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November 17th, 2019, 06:27 AM
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Confirm that the coolant is full. Confirm that the engine reaches full temp. If both are good then it is likely a bad valve or the vacuum supply to it. If you can get a Mityvac style vacuum tester, put vacuum to the valve and go for a road test. If it works the problem is in the vacuum supply to the valve, if it does not work with a known vacuum application the valve is bad or there is a lack of flow of coolant to the heater core due to air or a blockage.
Good luck!!!
Good luck!!!
November 17th, 2019, 09:05 AM
#12
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Confirm that the coolant is full. Confirm that the engine reaches full temp. If both are good then it is likely a bad valve or the vacuum supply to it. If you can get a Mityvac style vacuum tester, put vacuum to the valve and go for a road test. If it works the problem is in the vacuum supply to the valve, if it does not work with a known vacuum application the valve is bad or there is a lack of flow of coolant to the heater core due to air or a blockage.
Good luck!!!
Good luck!!!
November 17th, 2019, 09:43 AM
#13
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Well low and behold, it was 2.5 inches low...Also the over flow reservoir hose was curled up in the up position not touching the antifreeze...So I adjusted the hose and topped off the antifreeze in the radiator...I will test drive it tomorrow...Drove the 300C today into work...
November 17th, 2019, 11:03 AM
#14
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Great sometimes the simple answer could be the solution,been working on cars since I
Well low and behold, it was 2.5 inches low...Also the over flow reservoir hose was curled up in the up position not touching the antifreeze...So I adjusted the hose and topped off the antifreeze in the radiator...I will test drive it tomorrow...Drove the 300C today into work...
November 18th, 2019, 09:18 AM
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November 18th, 2019, 10:32 AM
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November 18th, 2019, 07:09 PM
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November 19th, 2019, 05:24 AM
#22
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Not in the heater. Low coolant means that there are air pockets in the cooling system. Air does not transfer heat very well, so any air that gets into the heater core means no heat out. I've had this happen many times on cars where the coolant level was low.
Back to the OP's problem, which is apparently NOT caused by low coolant. For diagnostic purposes, tee a vacuum gauge into the line that operates the heater control valve. Tape the gauge to the windshield so you can see it when you drive. Note the vacuum readings when you have heat and when it fails.
Back to the OP's problem, which is apparently NOT caused by low coolant. For diagnostic purposes, tee a vacuum gauge into the line that operates the heater control valve. Tape the gauge to the windshield so you can see it when you drive. Note the vacuum readings when you have heat and when it fails.
November 19th, 2019, 10:37 AM
#23
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Not in the heater. Low coolant means that there are air pockets in the cooling system. Air does not transfer heat very well, so any air that gets into the heater core means no heat out. I've had this happen many times on cars where the coolant level was low.
Back to the OP's problem, which is apparently NOT caused by low coolant. For diagnostic purposes, tee a vacuum gauge into the line that operates the heater control valve. Tape the gauge to the windshield so you can see it when you drive. Note the vacuum readings when you have heat and when it fails.
Back to the OP's problem, which is apparently NOT caused by low coolant. For diagnostic purposes, tee a vacuum gauge into the line that operates the heater control valve. Tape the gauge to the windshield so you can see it when you drive. Note the vacuum readings when you have heat and when it fails.
November 29th, 2019, 08:15 AM
#25
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Well my heater core blew up the other day.It was the original one.Put a new one in...BRASS...But im still having the same problem..I hooked up the mity vac gage and pump and im not loosing vacuum...checked the temperature of both hoses to heater core and went it get's cool, the temperature drops to about 110-120 degrees..when working properly, temps are 180 degress...so now im thinking it might be a bad thermostat??? so I will install a new one..180 degrees..Some how the antifreeze is not flowing through the heater core at high RPM'S..
November 29th, 2019, 08:29 AM
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November 29th, 2019, 03:31 PM
#28
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Bad T stat. I went through two bad ones (brand new chinaman units!) 0n my fresh 455 in my '64, and finally bought a high end unit (made in israel of all places!) and its good. On my '72 XGS, I had another brand new one fail and re-installed the 10 year old Dole T stat and its still in there. Thats 5 years ago.
Just an FYI... some heater control valves are either vacuum to open or vacuum to close (fail open/fail closed). Just because it has the numbers doesnt make it correct. The cold heater hoses lend me to think T stat however.
For winter you can bypass the HCV and run the system direct. ws
Just an FYI... some heater control valves are either vacuum to open or vacuum to close (fail open/fail closed). Just because it has the numbers doesnt make it correct. The cold heater hoses lend me to think T stat however.
For winter you can bypass the HCV and run the system direct. ws
November 29th, 2019, 03:44 PM
#29
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Bad T stat. I went through two bad ones (brand new chinaman units!) 0n my fresh 455 in my '64, and finally bought a high end unit (made in israel of all places!) and its good. On my '72 XGS, I had another brand new one fail and re-installed the 10 year old Dole T stat and its still in there. Thats 5 years ago.
Just an FYI... some heater control valves are either vacuum to open or vacuum to close (fail open/fail closed). Just because it has the numbers doesnt make it correct. The cold heater hoses lend me to think T stat however.
For winter you can bypass the HCV and run the system direct. ws
Just an FYI... some heater control valves are either vacuum to open or vacuum to close (fail open/fail closed). Just because it has the numbers doesnt make it correct. The cold heater hoses lend me to think T stat however.
For winter you can bypass the HCV and run the system direct. ws
November 29th, 2019, 03:57 PM
#31
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November 29th, 2019, 03:59 PM
#32
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The stat im getting is from summit... https://www.summitracing.com/parts/MRG-4364 …. good reviews..
November 30th, 2019, 06:30 AM
#35
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Go to a John Deere dealer and buy a 180 degree thermostat from there. It will fit and work perfectly. I was turned onto these from a friend who builds pulling tractors and street/strip engines for years. He has NEVER had one of these fail. It is what I put in my 455.I can get the part number if needed.
November 30th, 2019, 06:59 AM
#36
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Go to a John Deere dealer and buy a 180 degree thermostat from there. It will fit and work perfectly. I was turned onto these from a friend who builds pulling tractors and street/strip engines for years. He has NEVER had one of these fail. It is what I put in my 455.I can get the part number if needed.
December 6th, 2019, 05:53 AM
#39
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Problem solved..... Replaced the new thermostat and still did not work..I had a hunch and bought another heater control valve and installed it.. WALLA!!! It's working great now..Hard to believe i had two back to back bad heater control valves...Third time is a charm...
