checking for coolant leak at heater core

I have a 2006 Tacoma (2.7 L) with 325K miles. I took it on a road trip (2,000 miles round trip) a few weeks ago, which was a hard drive due to lots of wind. Also, it was very cold so the heater was on most of the drive. The coolant level in overflow tank was good before leaving but when I got back it was drained. The heat had gone out twice on the trip back (once on start up idling just didn't get warm but it was really cold) and then when I got back to town. No coolant smells, unusual amount of white exhaust nor any overheating/smoke from under hood noted.

I towed it to a shop and they inspected all coolant-related parts (water pump, lines, radiator, etc.) after letting it run idle for 30-45 minutes. They did not note any corrosion on water pump/radiator or signs of a coolant leak. Nor any discoloration in the oil. There is nothing dripping on the ground underneath the vehicle. I also cannot see any leaks from the overflow tank.

I know by now that my truck just doesn't lose coolant without something starting to go wrong (e.g., had to replace water bypass tube in past but that was also inspected by the shop this time.) You don't get a truck to that many miles without staying on top of an issue. I am driving it to my regular shop in a few weeks when they can fit me in, so keeping an eye on coolant level in both the overflow tank and radiator until then.

I've been reading about the heater core and related components and that seems a logical part to inspect for coolant leakage. There are no fluids on the floorboards and no residue/fluids seen behind the glove compartment. I would like to inspect the heater core and lines to look for dried coolant and overall condition.

Does anyone have a good source of information on how to access the heater core? (I have looked at diagrams but not clear on the best way to access.)

If it was leaking from around the heater core, will leaving the air off in the vehicle help to prevent further leakage events or does coolant continually circulate through the heater core?

Thank you for any help.

 

How much coolant did you actully have to add?

Did they pressure test the system?

I've never seen a heater core leak that didn't cause a coolant smell in the cab and/or visually leak from the box or out the A/C drain, 2nd gen Tacoma's have coolant running through them at all times.

You have to remove the entire dash and HVAC box to acces the heater core so you wana be sure that's your problem before you go after it.

 

This. ^^^^

You may be able to snake a boroscope into the heater core area with the Ventilation blower removed.

 

Thank you for the info. Good question, I added two overflow tanks worth but don't know if there was air in the system. I will be keeping an eye on the level from the radiator cap directly from now on, too, since they flushed the coolant so should be full.

I presume they pressure tested the system but not sure and will call to ask. They just said they checked everything they could think of for leaks and any corrosion on radiator/water pump, etc. I'll also make sure my regular shop does that to troubleshoot if it's a leak somewhere.

 

Great, thanks for the tip.

 

First and easiet thing to do if your only losing from the overflow is put a new radiator cap on it.

 

Thank you, I've looked at the cap. It's in good shape.

 

Check your radiator seams really close. Especially where the upper plastic portion joins the aluminum. If a seam is just slightly leaking, the fluid my be getting blown around by the fan and it might not be real visible.

 

Will do, thank you.