1999 Tahoe Z71 Coolant Questions and Issue

[Kent2500]

Q1. My temp gauge on the console (once warmed up which is pretty quick) is steady at about 185. Far as I can remember, always been that way and I assume normal?

 

Q2. The radiator cap controls the flow of extra fluid back to the reservoir tank? How often do the radiator caps fail (as in requires more pressure than 15psi to release fluid) and require replacement?

 

I have this weird issue of no overheating (hot 90+ day, AC running, local traffic, no issues). But the reservoir tank is empty. If I fill (engine cold) to the cold line, then after a short local drive it appears that coolant is just shooting out of the engine (appear to be the water pump). Like two cups just pours out of the front/bottom of the engine area. But then it appears fine. If I check the fluid in the radiator (engine cold), maybe 2" from the top, covering the top set of fins. This condition might have been going on for a year or so. (Yep, I shouldn't have ignored the empty reservoir tank issue, but then the dealer never comments on it either so that two of us).

 

Being a total newbie, my wild theory is the radiator cap is sticking and letting the coolant system hit very high pressures which blows out coolant. But once the level drops to a specific level, the 2" or so of air in the radiator becomes a buffer for the pressure and doesn't reach that high. Everything is happy over months of driving. But if I fill the reservoir tank then I start the cycle again. If correct, a simple radiator cap replacement will correct the issue. (And maybe stuck with a water pump replacement). Or I could be wrong and something else is going on.

 

Additional thought, almost as if something near the water pump (or the water pump seal) is acting like a pressure relief valve and dumps at some pressure or okay (more or less) below that.

 

I have ordered one of those radiator/radiator cap pressure testers kits to acquire more information. Unknown if that kit will verify the radiator cap/reservoir tank interaction or not (or just tests the cap can maintain pressure).

[Doug_Scott]

Typically rad caps fail in the other direction, by releasing pressure too soon. Keep in mind that the reason for the cap holding pressure on the cooling system is to simply raise the boiling point of the coolant. Once the cap vents, coolant coming out can be in excess of 230 degrees, and will instantly boil violently. The steam released is also somewhat superheated, both of which will give severe burns instantly.

 

Water pumps generally leak at certain pressures, and they will leak from the vent hole visible from underneath, close to where the pulley sits. You will see a stain from that hole running back along the snout of the water pump, then down the front of the block.

 

Reservoir should be kept at proper level. The hose from the rad to the reservoir must not have any leaks in it, as well as the line that goes down into the lower level of the tank. If the hose leaks anywhere, it will not draw coolant back into the rad as it cools down and pressure drops.

 

Most shops have a tester for rad caps, and I would imagine the bigger auto parts stores do as well.

[Kent2500]

I pressured tested the coolant system and at 15psi there is a serious leak out of the front of the water pump. (like streaming out). Appointment tomorrow for my local dealer to replace.