GMC Yukon Diesel: Low Coolant Warning Signs & Fixes

I had a similar issue with my 2021 GMC Sierra diesel last winter. I have some experience working on cars but leave complex cooling system issues to professionals. The check engine light and low coolant level definitely needs attention soon to prevent engine overheating. While my engine was also running fine initially, I noticed the radiator fluid was consistently dropping below minimum. Took it to the shop where they found a faulty sensor wire connection near the coolant temperature sensor. They had to replace the connection and properly bleed the cooling system to remove any air pockets. Total repair cost was 95 Euro including diagnostic and labor. The water pump and head gasket were fortunately fine in my case, but its important to fix coolant issues quickly before they cause more expensive damage. What year exactly is your Yukon and how long have you noticed the coolant level dropping? Any sweet smells from the engine bay or white smoke from exhaust? These details would help determine if you might have similar sensor issues or potentially something else. Have you checked if the coolant level drops consistently or was this the first time you noticed it low?

After checking last week and noticing another significant drop in coolant level since my initial post. Looked closer and spotted small puddles under the vehicle when parked overnight. The cooling fan seems to run more frequently than usual too. For reference: Last service was 2 weeks ago at 149861 KM. No white smoke or sweet smell noticed yet. The coolant leak appears to be getting worse though, losing about 1cm in the reservoir every couple of days now. Going to schedule a pressure test to pinpoint where exactly the coolant is escaping. Thanks for sharing your experience with the sensor issue, hoping its something similarly straightforward in my case rather than head gasket problems.

Thanks for the update on the coolant situation. Based on your description, your symptoms point to a different issue than what I experienced with the sensor. The consistent coolant loss and visible puddles strongly suggest an external leak rather than the electrical problem I had. The increased cooling fan activity combined with the visible leaks could mean the system isnt maintaining proper pressure. Sometimes this happens when the radiator cap loses its seal, but given the puddles, you likely have a physical leak in a hose or connection point. When my Sierra had the sensor issue, there were no visible leaks. Your situation seems more straightforward to diagnose but potentially more involved to fix. A pressure test is definitely the right next step to locate the exact leak point. Watch the coolant reservoir level closely until you can get it checked. If the loss rate increases or you notice the engine temperature climbing, consider limiting driving to prevent engine overheating. These diesel engines are robust but expensive to repair if they overheat. Keep us updated on what the pressure test reveals. The repair cost will vary significantly depending on whether its a simple hose replacement or something more complex.

Given the dropping coolant levels and puddles showing up under my Yukon, I decided to take immediate action. Had the pressure test done yesterday and it revealed two failing radiator hoses with significant cracks near the clamps. The cooling fan running frequently was apparently compensating for the reduced coolant circulation. The mechanic also found slight corrosion around one of the connection points. Total repair including new hoses, clamps, and a complete system flush came to 285 Euro. Definitely worth addressing it quickly before risking engine overheating or more serious problems. The engine temperature is now staying steady and no more puddles under the vehicle. Really glad I caught this before it developed into head gasket issues or other major cooling system problems. Will keep monitoring the coolant levels just to be sure everything is properly sealed. Thanks for the advice about getting it checked promptly. Better to fix a few radiator hoses now than face bigger repairs later.