Coolant related question

[jbt56]

So, this may be covered somewhere, although a search didn't find it.

I recently bought a one-owner, beautifully maintained 99 Suburban C1500. I've replaced a few small parts (bulbs, stereo, like that), including the coolant temp sensor in the block and the thermostat. Interestingly, the temp gauge still won't go over about 1/4 up the scale and, more worrying, the lower rad hose remains comfortably touchable even after driving several miles. The engine has not shown any signs of being excessively hot at any time since I've had it (about 6 weeks) and no warning lights have come on while driving. I'm out of ideas; does anyone have any suggestions as to what to look at next?

 

[Dgonz]

So, this may be covered somewhere, although a search didn't find it.

I recently bought a one-owner, beautifully maintained 99 Suburban C1500. I've replaced a few small parts (bulbs, stereo, like that), including the coolant temp sensor in the block and the thermostat. Interestingly, the temp gauge still won't go over about 1/4 up the scale and, more worrying, the lower rad hose remains comfortably touchable even after driving several miles. The engine has not shown any signs of being excessively hot at any time since I've had it (about 6 weeks) and no warning lights have come on while driving. I'm out of ideas; does anyone have any suggestions as to what to look at next?

You May have a clogged radiator

 

[jbt56]

You May have a clogged radiator

So, an update. BTW, thanks, Dgonz, your thought was echoed by a local tech I trust and a test. I used a laser temp gun on the rad tanks and found the inlet side hot- about 170+- degrees, while at the fill tube, the tank and coolant were at about 80. The radiator was replaced yesterday- not a terrible job, although messy.

Sadly, there has been no change in any symptoms. The temp gauge still reads at about a quarter up the scale, the coolant at the radiator cap is still cold after 5-10 miles of driving while the upper hose is 160-170 degrees and the lower hose remains cold. A couple of other things noted are that the system will not build any pressure- before or after the thermostat and radiator- and the heat blows very hot, while the A/C blows very cold. One other thing- this truck has not once shown any sign of overheating. We recently had a week-long heat wave during which I was driving this thing in 100+ degree traffic with both A/C systems cranking and had no trouble whatsoever with engine heat.

I'm an okay 'parts replacer', but am at the end of my knowledge as fas as diagnostics. I'm thinking water pump at this point, simply because there just isn't that much more to the system. Any further ideas are welcome!

 

[sntrym]

I'd go with the water pump. The water pump may have enough ooomph to push the coolant through the big spaces in the block and manifold, and the heater core, but not enough to get it through the radiator. The circulation system doesn't need the radiator to work but since you stated the heat was very hot I would guess the heater core is functioning as the radiator.

What is the temp of the intake manifold and heads after running for a bit?

You could also have a bad new radiator. Not likely but new parts aren't always good.

 

[Tom P]

So, this may be covered somewhere, although a search didn't find it.

I recently bought a one-owner, beautifully maintained 99 Suburban C1500. I've replaced a few small parts (bulbs, stereo, like that), including the coolant temp sensor in the block and the thermostat. Interestingly, the temp gauge still won't go over about 1/4 up the scale and, more worrying, the lower rad hose remains comfortably touchable even after driving several miles. The engine has not shown any signs of being excessively hot at any time since I've had it (about 6 weeks) and no warning lights have come on while driving. I'm out of ideas; does anyone have any suggestions as to what to look at next?

What type brand/degree/type of thermostat did you buy and replace? Experienced similar issue in my k3500 when I bought it. Truck never warmed up no matter what I did/towed. Thermostat was stuck wide open. I replaced it with a new Delco. Some thermostats have a safety feature that will lock itself open if it gets too hot. I suppose its possible that your new thermostat is defective/ stuck open or your engine started to overheat the first time you ran it, and popped the safeties.

 

[jbt56]

Where I can get a shot with the laser thermometer, the external engine temps are in the 200 range. Right below the thermostat, I saw about 190, with the actual housing being about 145-170, which continues to the top hose.

The thermostat is a 195 degree, which is spec, and is at least 'good' quality. Don't remember the brand, but it came from Rock Auto. The radiator is a Spectra (?) from Auto Zone. Seems like a decent brand.

The most baffling part of this whole thing, to me, is the engine has not overheated at all! I can open the hood on a 90 degree day, with the A/C blasting, and there's no excess heat. It's just weird.