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Discussion Starter · #1 ·
I have a 1998 s10 2.2 that doesn't have heat. I've changed thermostat from a previous stuck open thermostat and still no heat. While trying to figure this out I noticed that the radiator doesn't build pressure. I can drive for a hour and can take radiator cap off without any coolant rushing out. I've also let it idle for 30+ minutes without it boiling over without the cap. Water pump is new as well. Any suggestions?
 

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2003 Sonoma SLS ext. cab 4.3L / 4x4
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Welcome to the Forum - glad to have you aboard. The following comments are not intended to be snide or derogatory, but more complete and specific information (& quantifiable variables) are really needed to even try to offer any remote diagnostic suggestions. The more accurate information that you can provide can help the folks here offer advice on how to proceed and what may be/ or is the problem.

What's the mileage of the vehicle? Have you had the system pressure tested? Are you sure the radiator cap is good? When you say 'no heat', are you referring to heat in the cab, or 'no heat' as in not registering on the temp. gauge? If it's no heat in the cab, it's possible that your heater core is plugged with sludge/ debris. What is the temp. reading on the temperature gauge, and under what conditions? When you changed the t'stat, did you flush/ backflush the entire cooling system radiator/ engine, heater core? When was the last time the coolant was changed (if known) and what condition is it in (the color is a good clue)? What is the coolant level like, and have you had to add any? Are you certain there is no trapped air in the coolant system? When you remove the radiator cap after driving - when is that done? - immediately upon shutting off the engine, or a certain time interval after the engine is turned off?
 

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Discussion Starter · #3 ·
Truck has 146k miles. The truck has brand new radiator cap water pump and coolant less than 200 miles ago. I found this problem while trying to address a no heat inside cab issue. Once I replaced thermostat the truck gets up to temperature on the dash gauge now but still no cab heat. My coolant Temp sensor reads 195 give or take. I have tried flushing heater core on both inlet and outlet. The coolant level never drops. When i say I can remove the cap I can do it while truck is running or when it is shut off no matter how warm the engine is
 

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Truck has 146k miles. The truck has brand new radiator cap water pump and coolant less than 200 miles ago. I found this problem while trying to address a no heat inside cab issue. Once I replaced thermostat the truck gets up to temperature on the dash gauge now but still no cab heat. My coolant Temp sensor reads 195 give or take. I have tried flushing heater core on both inlet and outlet. The coolant level never drops. When i say I can remove the cap I can do it while truck is running or when it is shut off no matter how warm the engine is
Are heater hoses the same temp...+-
 

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I am stuck on removing the radiator cap when at operating temperature and nothing runs out. Cooling system should be pressurized when operating temperature is reached....opening the rad cap at that point is rather dangerous as hot-as-**** coolant would erupt upward and outward. Something major league wrong here...do you have sufficient coolant?
 

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2003 Sonoma SLS ext. cab 4.3L / 4x4
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I am stuck on removing the radiator cap when at operating temperature and nothing runs out. Cooling system should be pressurized when operating temperature is reached....opening the rad cap at that point is rather dangerous as hot-as-hell coolant would erupt upward and outward. Something major league wrong here...do you have sufficient coolant?
Yep - that has me puzzled as well. By definition, under normal circumstances, the cooling system is a closed loop pressurized system. If there is no pressure, then, again by definition, there is a leak somewhere in the system. But, apparently (and as stated) "the coolant level never drops". It seems like there is a key piece of the puzzle that remains missing and/or there are some outstanding questions that remain unanswered. I'm still leaning toward the heater core being blocked to explain the lack of cab heat, but the lack of pressure in the system certainly warrants further analysis.
 

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Discussion Starter · #8 ·
I am stuck on removing the radiator cap when at operating temperature and nothing runs out. Cooling system should be pressurized when operating temperature is reached....opening the rad cap at that point is rather dangerous as hot-as-hell coolant would erupt upward and outward. Something major league wrong here...do you have sufficient coolant?
I can drive the truck without a radiator cap and coolant doesn't overflow. I can let it idle for an hour and coolant doesn't rise and it will not overheat
 

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Discussion Starter · #9 ·
Yep - that has me puzzled as well. By definition, under normal circumstances, the cooling system is a closed loop pressurized system. If there is no pressure, then, again by definition, there is a leak somewhere in the system. But, apparently (and as stated) "the coolant level never drops". It seems like there is a key piece of the puzzle that remains missing and/or there are some outstanding questions that remain unanswered. I'm still leaning toward the heater core being blocked to explain the lack of cab heat, but the lack of pressure in the system certainly warrants further analysis.
I have read it may be a leak very high in system I will rent a pressure tester this weekend and see if I can find a leak
 

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Both hoses Luke warm
I'm not trying to be snotty, but "lukewarm" really isn't too meaningful. What would be much more helpful is a temperature reading of each hose, to determine the temperature delta between coolant inflow and outflow. If they are very close to each other, that is a prime indicator of likely core restriction/ blockage.
 

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I have a 1998 s10 2.2 that doesn't have heat. I've changed thermostat from a previous stuck open thermostat and still no heat. While trying to figure this out I noticed that the radiator doesn't build pressure. I can drive for a hour and can take radiator cap off without any coolant rushing out. I've also let it idle for 30+ minutes without it boiling over without the cap. Water pump is new as well. Any suggestions?
Not to throw any mud here but I ran into this some time back with a vehicle as well. Some folks believe that the coolant used is designed to help keep your engine from overheating and or freezing up in the winter. So, by nature, individuals will put in straight coolant to get maximum protection, so they believe. It is quite the opposite. If there is too much coolant and not enough water in the mixture your system will not heatup thereby not causing any pressure from the heat to build. Just passing this one as a possible check point. As for in the cab there is ristat that helps in the temperature are for the heater controls check that as well had to replace the one I had in my 96 blazer.
 

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New water pump failure, not pumping? Vanes seized and slipping on shaft? Was it good for a while with the new pump? Is this why you changed the waterpump?
 

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I have tried flushing heater core on both inlet and outlet.
was water flowing freely both directions when you did this? was it plugged? what happened? As of right now, you have no heat, this is the most important thing of this entire post. water not flowing, nothing coming out of the cap, totally useless info, we need to know what happened when you flushed the heater core.
 
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