Running sooo cold....brrrrr.

[Portland Suburban]

Here is my problem:
Temp gauge shows low engine temp less than the 1st bar. This is consistent with low heater temps and quick cool down after sitting for very little time. Ambient temp is usually between 25 and 75 degrees here in Portland.

I bought this suburban used with a number of add ons including a heavy duty hitch, external oil and Transmission Cooler. It also appears that the radiator is larger and stock. I assume that the water pump may be larger than stock.

Assumption: 1)thermostat is stuck open allowing unrestricted flow. 2)Coolant is flowing from crossover pipes into heater core and back into radiator essentially allowing coolant to pass from engine to radiator even at low temps.

Attempted Solution: 1)Replace thermostat with mr. gasket 180 degree unit.

Outcome: Temp now is lower. Coming down the backside of Blewett Pass, temp dropped below 100 degrees consistent with heater temps.

Hypothesis: Thermostat is opening allowing small bypass. Water is bypassing thermostat into heater core and thereby into radiator allowing for cooling when none is needed. Engine is not under load and therefore is not generating sufficient heat.

Possible solution: Install 195 degree thermostat. Reroute return line for heater core back into water pump to negate cooling effect into primary radiator.

Am I on the right path?

[ZZ]

Does the water in the overflow tank swirl and/or have air bubbles when the engine is running? If so, the engine has a blown head gasket or cracked head. The engine will run cold and you will have no heat.

I hope this isn't the case. I've been through it four times with GM diesels.

[Portland Suburban]

Hmmmm, I don't think so but will check tomorrow. I do notice that when I rev the engine the level in the radiator drops. Other than that, only a few bubbles after refilling the system with 50.50 antifreeze.

[Portland Suburban]

Well, I have a 195 degree stant on there now. Wow, avoid the 180 degree mr. gasket. What a piece of crap. Anyhow, I know that not everyone will agree with me, but the way the heater core is routed on mine is utter garbage.

It goes like this:

Cold:
Water Jackets-Heads-Crossover (past thermostat)-heater core-!!Radiator!!-lower hose....

Now, tell me this. Why the heck to do you want the heater core to act as a 1" tubing bypass for the thermostat? Hmm? Gm...what were you thinking?

Dumb. Really Dumb-in my opinion.

[Portland Suburban]

Well, I have a 195 degree stant on there now. Now, I have heat again. I am not sure if the temp gauge is correct, but for now I have heat again. Once I get the aux. sender unit on there, will know for sure.

Wow, avoid the 180 degree mr. gasket. What a piece of crap. Anyhow, I know that not everyone will agree with me, but the way the heater core is routed on mine is utter garbage.

It goes like this:

Cold:
Water Jackets-Heads-Crossover (past thermostat)-heater core-!!Radiator!!-lower hose....

Now, tell me this. Why the heck to do you want the heater core to act as a 1" tubing bypass for the thermostat? Hmm? Gm...what were you thinking?

Dumb. Really Dumb-in my opinion.

[BobND]

Portland,

The heater return dumps into the RH radiator tank, above the tranny cooler (assuming it's got a slushbox), flows down past the tranny cooler, to the water pump's suction hose. It probably doesn't get cooled much, as the flow is NOT across the core.

I assume they did that to get some coolant flow past the cooler while the thermostat is closed.

I am in COLD (well, not this winter, so far) northern ND, and the diesels need to retain all the heat they can when it's bitter cold outside, so I re-route the heater return to the inlet sude of the water pump, by removing the pipe plug there, and installing a hose nipple. On my 6.2 Sub and pickup, I remove the radiator fans for the coldest months. I generally do not tow with them, and just the airlow while on the road cools them, and they generally can idle for quite a while without overheating.

[Portland Suburban]

Well then , I should be in the clear as my coolers are both external. Can you tell me what size nipple you used? That would save me quite a bit of time.

Thanks,
Chris

[BobND]

IIRC, 1/2" NPT, and, of course, the hose barb end is 3/4".

[john8662]

I notice something similar on REALLY cold days with the hi-flow Robertshaw stat or the "Mr. Gasket" stat, which is probably a repackage R.S. stat.

The stat still flows some coolant, and the engine doesn't get terribly warm, usually in between the bone cold mark and the second mark on the gauge. But, I still have heat in the cab after the needle just baraly lifts off the bone cold position on the gauge. After recently servicing the heater core, since the engine's out, I noticed that it was REALLY clean on the inside, it didn't leak, but I was in there fixing other stuff. So, what I'm getting at is that maybe you have a partially plugged heater core, that only works when you've got enough heat to overcome the deposits in the core itself and conduct the heat to the core and into the air.

In my opinion, a Stant stat has no place in the coolant passage of a 6.2! But, I base this mainly on my observations during hot summer months in Texas. The stat when under load will open, then fully close, then open, etc. This can be seen as wide temperature swings on the gauge. For example, the first opening for a 195 stat will be close to the 210 mark on the gauge, when the stat opens you will notice the gauge go down. This will continue throughout the operation of the engine. The R.S. design stat is "balanced" in that it partially opens and regulates the coolant temperature, So you don't get the wild temp swings.

Here in hot climate months, if pulling, the stant will get the system too hot, to where it cannot recover and will tend to run hotter or overheat.

I was also nervous letting the engine idle with the Stant, because it would seem as though if you didn't have good coolant flow (slow turning water pump) that the stat wouldn't open.

A way to make a Stant decent is to drill a 1/8" pilot hole somewhere in the stat (away from the port opening), this gives the stat a small bypass, and seems to help level it out.

The idea stated by Bob ND above about re-routing the heater core input and output was used on the earlies 6.2's. I remember reading in a service manual update that said to re-route the heater core tubing to reflect what we've got not. Before, it used the auxillary port on the waterpump.

I agree that the way it's routed probably does provide some kind of safety margin (which IS needed), in conjunction with the bypass already connected to the crossover into the waterpump.

[Portland Suburban]

Well, I have heat now and have yet to get a corroberated reading on the water temp. So, for now, I will focus on other issues. Yes, I get the swings, but it is not so bad. Overall, it moves a bit. However, the pilot hole is a good idea. As I have said before, it would seem that a system in which I could choose the quick heat idea in the winter and the bypass in the summer would work well. All I would need is some hose and a valve. Wala!