2015 Suburban Running Cold

2015 Suburban · February 8, 2021

Morning all.

I have a 2015 Suburban (new to me in December of 2019) and runs cold.

I have a scan gauge, and the coolant temp rarely goes above 170 in the summer, or above 155 in the winter while driving. The gauge on the dash works, and confirms it running cold.

If i sit and idle, it will creep up to 185, then the fan comes on and it will go back down.

I took it to the dealership I bought it from, and they let it idle and said the thermostat works fine but did not address the problem.

im glad to have the seat heaters because its difficult to get it warm enough inside unless I put the heat up to 75 and the fan on full..

Thoughts/ questions

CamGTP · February 9, 2021

Get a new OEM thermostat.

It may be working but it's not working at the factory specs. These engines should run between 200-215 almost all the time. I had to replace mine before this winter because I could barely get above 180 degrees in the winter.

Grumpy Bear · February 9, 2021

13 hours ago, 2015 Suburban said:

Morning all.

I have a 2015 Suburban (new to me in December of 2019) and runs cold.

I have a scan gauge, and the coolant temp rarely goes above 170 in the summer, or above 155 in the winter while driving. The gauge on the dash works, and confirms it running cold.

If i sit and idle, it will creep up to 185, then the fan comes on and it will go back down.

That is too cold. 175 F minimum fully warmed up is minimum. Factory thermostat is 207F. Some Corvettes and like performance Gen 5 motors use a 196 F factory thermostat. It will creep up because no air is moving over the radiator while sitting. 185 F as a switching point is also off. I think factory fan on trip point is 210 F. Cameron will correct me if I error in that regard. He knows that stuff better than I do.

It could be the previous owner installed a 160 F stat and lowered the fan trip but normally that can't be set lower than 192F. Point is that a factory stat and this low trigger point will fight each other.

flyingfool · February 10, 2021

check and see if the fans are always running or off.

previous owner might have a tune installed on it and this is screwing up the fan operation, the fans also go into failsafe on always, when the thermostat is stuck open too.

Edited February 10, 2021 by flyingfool

2015 Suburban · February 19, 2021

I called 2 shops (one local and one regional). both said the book said this was a 4 hour job plus a coolant flush.

is this something I can do in the driveway. maybe tilt the hose up and hold out of the way, replace the housing, reinstall the hose, and top off coolant as needed?

CamGTP · February 19, 2021

They must not have the correct vehicle for this. It's a 20 minute job.

Here is a video on it. The title is not correct but it's the same engine that you are working with.

Just put a drain bucket or pan under the front, it'll catch what comes out. When I finish the install I always just grab a bucket of hot water and dump it over the area the coolant spilled over. Maybe two buckets if you need to. I usually back the truck out onto the driveway or street when I dump the water all over it so I don't do it in the garage.

2015 Suburban · February 19, 2021

i was confused by a 4 hour job for a thermostat as well. the part is ordered, ill update once I install it..

2015 Suburban · March 7, 2021

got it swapped out this afternoon. a little messy, but it really was 20 minutes, including clean up time. drove it around the neighborhood and it would hover between 200 and 205 on the scan gauge. the test will be the 40 mile drive to work on Tuesday, but as of now, I think its good--thanks for the advice and steering me away from a shop.