5.7 Vortec won't reach 195 degrees.

[redfishsc]

In a 99 K1500 Sub. Cannot get engine to go higher than 170. Verified via OBD2 scanner, the upper temp sensor "matches" the dash gauge which reads from the cylinder head. Outside temp as high as 70 degrees.

First tstat was a Motorad 195.

Second is a Delco 195.

Neither was installed upside down. Spring side (bigger side) down toward engine block.

Upper radiator hose won't get more than "fairly warm" and heater doesn't blow quite as hot as my other 1999 Sub does (also a 195 tstat, not sure what brand is in it)

Would a faulty radiator cap prevent it building pressure but NOT barf out coolant?

Truck looses NO coolant. Stays full.

 

[shamrock246]

I would test the t stat you have out in pot of water and heat it up to see what temp it opens at.Can you switch caps with your other Sub to see if that helps? Any chance the system still needs to be burped?

 

[redfishsc]

Well apparently it was running the right temp all along.

I forgot I had a spare coolant temp sensor (upper one for the ecm). I bought it a couple months ago by accident trying to get the sending unit for the dash on my other Sub.

I swapped it out, warmed up the truck, and it spooled up to 194. I was holding the upper rad hose (which is painful when it's 20 degrees outside and the fan blowing on your hand.

As soon as the OBD2 dashboard on my phone read 194, I felt the hot coolant flow through.

It did not seem to build a whole lot of pressure sitting there idling, but I never see coolant leaking through the cap, so I don't know if it's actually building pressure properly or not. But it never barfs out of it.


I'm going to assume that the heater is just not as efficient in this truck because I know the guy that owned it several years ago had filled the thing with head gasket stop leak. I probably don't have it completely flushed out, and I'm not even going to bother here in Charleston, it still gets warm enough to warm the cab up. Oh my C 1500, it gets hot enough to steam shrimp, which is a nice thing I'll never actually need here.

The dash readout still only shows about 170, and that particular coolant temperature sender is absolutely brand new, maybe just the old dashboard gauge is wonky. I know my C 1500 it reads the same way, it always shows reading around 160 to 170 but the ECM reads 190 to 195 pretty much all the time.

I would test the t stat you have out in pot of water and heat it up to see what temp it opens at.Can you switch caps with your other Sub to see if that helps? Any chance the system still needs to be burped?

This is exactly why I love having two of the same truck lol. I can swap easy parts for free.

 

[shamrock246]

Your scanner reading had me fooled also. My dash gauge reads right below the 210 mark witch matches my IR gun temp reading of 205 at the cyl head near the sensor. My scanner temp is 188 to 192 witch is about what i get on my IR gun in that area. I would back flush that heater core again not sure what would break down stop leak so you could flush it out. I must have one of the unicorn dash clusters all my readings are really close just haven't verified the oil pressure. Aside from the volume of air coming out the front vents the heat and air in mine are great.

 

[redfishsc]

Clean your evaporator coil if you have lousy airflow. Even slight clogs really bog them down

 

[DerekTheGreat]

My '89 had practically no heat until I flushed the system out. I went so far as to take the hose going from the HC to the radiator off & running water through that hose to clear the crud out and then refilling the entire system with prestone flush treatment & running the truck for about 30 minutes with no thermostat. Rinsed it until no more rusty water came out, refilled & it's been great ever since. Used a 195 Stant thermostat cause I want hot heat when it's 5 degrees out lol. I've had the blend door stick on me and the thermostat stick closed once though too. Weird.

 

[shamrock246]

Clean your evaporator coil if you have lousy airflow. Even slight clogs really bog them down

I tried that twice and didn't get much improvement.When i had the dash out a couple of years ago to replace the air door assembly and fiber glass up the cracked dash i could see the the back side of the evaporator. So ran the blower and had good airflow up until it got to where the air doors are then it seemed to stall out real bad as it tries to make the right angle turn upwards maybe i can look into it some time in the future but i can live with it for now.

 

[Ken K]

I have seen too many evaporators grow a furry coat, restricting air flow. As well, GM uses a door to by-pass the heater core for A/C operation, depending on the type of control, like vacuum, the door may be letting in cold air because it is not shutting. I have witnessed inop mode doors due to a drinking straw or plastic something that fell thru defrost vent and some sucked out of glove box. Most of these issue were covered in previous post.

I am not sure if it applies to your year but a GM TSB indicated loss of heat after aftermarket radiator due to the small hose fitting is plugged with factory plastic that allows it to fit more years of vehicles. With the nipple plugged and instruction show its' removal. Everyone reads the instructions...Right? No coolant flow causes cavitation inside the water pump and little hot coolant flow into heater core. Just saying as i no longer have access to GM's eSI (electric service information). TBS can be found elsewhere online. Best of luck!