Need More Heat... How?

[painthorsman]

This is kinda frustrating... pulled a 454 that produced too much heat now I have an engine that doesnt seem to produce enough. On cool mornings there is so little heat from the heater core untill I drive it awhile (1/2hr) that one of these days I will be an icecicle before I get to work...
I installed a new 195 degree NAPA thermostat the other day and it seemed to help a little but not enough (isnt the themostat supposed to be "special"?) The one for the powerstrokes and the cummins engines are made special.. this looks like a "will fit". I looked for bubbles in the water with the engine running, that would indicate that there might be a combustion leak that would prevent good heater operation ( a notorious malady with 6.2 diesels) and found no bubbles... what next?
The heater hose routing runs from the head crossover, to heater core and then to radiator... exactly the way it shows in the GM shop manual. Why is GM different? Most everyone else, including GM in the "old days" goes from water outlet to heater core and back to water pump. It seems like the heater core is drawing water from the engine via the radiator, cooling it through the heater core and returning it to the radiator... without ever allowing the water to get fully "hot". There is a pipe plug on the water pump that would allow a return hook up there... can this , should this be done? will it help?
Suggestions an Comments appreciated! smile.gif

[mhagie]

Do you have a temp gauge? what is it runing? if so what sender did you use 454 or 6.2?
As for heater hose routing one should remember the flow of the cooling water,it leaves radiator at the bottom thru water pump where it is pressurized thru engine leaving engine at thermostat housing returning to radiator.
The heater therefore receives preassured water from crossover returning it to the radiator tank. this design is not exclusive to the 6.2 as the biggest share of the same year small blocks were likewise.
One possible check is to use a pair of vice grips to pinch off heater hose and with a cold engine remove rad cap start engine and observe the water at top or rad if it shows water circulating somehow water is passing thru thermostat thus cooling the water prematurely.
the t/stat has to hold back the water in order for engine to obtain normal operating temp, then open to maintain said temp.

[painthorsman]

I used the sending unit that was in the 6.2 when I got it. The temp gauge on the dash reads about 1/4 inch or not quite to the first mark to the right of the cold mark when fully warmed up (the gas engine I took out, would put the gauge at or a little over the halfway point when warmed up). I havent taken an acutal temp of the water leaving the t housing. I think I should be able to get fairly accurate with a temp probe on my flukemeter. What I was getting at on my earlier post was... that the heater core, the way the return hose is routed to the radiator, is acting like a radiator outside the loop of of the thermostat... in effect cooling the engine prior to thermostat setting. There is a LOT of water travelling through the 3/4 inch hose coming from the heater core, that doesnt have to pass through the thermostat, but just dumps straight into the radiator.

[da4wheeler]

I had a similar problem with my 350 gasser when I lived in Michigan. The first thing I did was get a fan clutch that worked off of thermostat/heat value instead of the overspeed/centripital type. That didn't do a whole heck of a lot. Then I seized on the same concept that you are seeing with the heater/radiator setup. On the 350 water pump there is a plug on the top side. To be absolutely sure, I pulled it, hooked up a pipe nipple, and a hose to a bucket full of water. Starting the engine started to suck the bucket empty, so that was on the low pressure side of the pump. (Take off the radiator cap and be ready for a mess). On the side of my 6.2 water pump, there is a similar pipe plug. I suspect it is also on the low pressure side of the pump.

Re-routing the heater hose return from the radiator to the pump resulted in my 350 going from about 30 minutes to open the t-stat on a cold ( 0 degree ) day to about 8 minutes. This of course, included the extra benefit of heat and defrost faster. I would suspect that the same thing could be done with the 6.2

A note, now that I live in the desert of California and summertime temps hit well over 100 degrees, I still have not had any problems with the 350 overheating with the aforementioned setup. I am planning to do something similar to my 6.2 with the next coolant flush/fill. I was lucky and had a threaded fitting where the heater core water returned to the radiatior in the 350, it took a pipe plug no problem. I'm not sure if the 6.2 is the same, it might need a short hose and a plug.

Good Luck.

-Nate

[gmctd]

The 6.2 is not a great generator of heat. You'll need the correct 195 deg thermostat for correct response. Then, you may notice the coolant temp rise to 200deg, then drop like a shot back to 180deg as the tstat opens, then the slow rise to 200 again after it closes. It is more stable with the ac running.
The heater hose routing is correct. The water pump pulls water from the radiator cool tank, where the engine oil cooler is located, forces it thru the block, against the closed thermostat. The engine-heated water then bypasses the tstat thru the heater outlet tap to the heater, and back into the tank.
Remember, water flow across the radiator is very minimal when the tstat is closed - a very small bleed hole ensures trickle flow.
And, you'll notice there is no vacuum-controlled heater shut-off, as had been used with the gasser blocks.
With a properly functioning tstat, this routing of the heater hoses ensures the engine oil temps are stabilzed in colder weather. Could be why the early blocks do not suffer from main-web cracking, as do the late blocks, where the oil cooler is external. The later cab-and-chassis and HD 6.5 trucks also had the cooler in the radiator.
It also ensures constant flow thru the block and heads, preventing hot spots at the rear cylinders.

That tap on the water pump is for tstat bypass hose, where the water pump constantly circulated water thru the block when the tstat was closed. The tap is on the intake side of the impeller.
It was used thru end of 6.5L production to stabilize engine temperatures.

The temp action I related above was in my '89 6.2 3500 crew cab, T400 and 3.25 final drive. Even with all that weight and relatively high gearing, water temps would cool immediately as the tstat opened.
Meaning the 6.2 is not an intensive heat generator.

jd

[DYNA]

I,ll have to agree with gmctd.My 6.2 on a cold nebraska day would not ever open the thermostat,with the heater on high! Although the temp gauge would run upwards of 195. The radiator would be cold to the touch.But initial warm up was excellent.I would look into possible scale build up in your core .Preventing proper heat transfer to the air box.Also is the air door in the heater box fully closing, stopping the mixing of cold outside air with your heated air? Good Luck and don't freeze. Dyna

[dieselhumvee]

Just an FYI, the 6.2 in my old 1993 hummer warms up rather quickly, in about 3 miles the heater puts out warm air. The dodge cummins I used to drive took forever to warm up, 6 or 7 miles. The hummer runs a steady 180 in the winter and rock solid 190 in the summer. I think that with such high compression a 6.2 should warm up quickly.

[NH2112]

My 6.2 would never put out a lot of heat, either, even before I went to the 180* thermostat. My "solution" was to simply make a winterfront to cut down on cold airflow through the radiator. I know it's not really a solution, but more like a field fix, but it did work.

[gmctd]

Big rigs are factory equipped with a set of "venetian blinds" on the radiator for just such purpose.

jd

[britannic]

My 2003 Duramax was shipped with a winter radiator cover for the same reasons. Diesels are more efficient and so have less waste heat and lower operating temperatures than an equivalent gasoline engine, which is why restrciting airflow through the radiator on a freezing winter's day is necessary.

[Kadzban]

On my truck the heater quit working a couple winters ago. I changed the T-stat to a Robert Shaw 180 for a Chrysler big block I think. Summit sells them. They are "High Flow" they say. Different design anyway. Looks like the stock GM one I pulled out. Anyway while I was at it I pulled both heater hoses off and ran the garden hose through it. That fixed the heater. Now it warms up really quick. Maybe GM used a different heater core in the 6.2 to compensate for the lack of heat.

[gmctd]

In reviewing this discussion, I noted it defined the problem without addressing it.
A few more points -

Those with factory-installed 6.2L engines may have noted an unusual arrangement for the auto trans cooler and lines, where it is plumbed into the hot driver-side radiator tank. Cool coolant is required to reduce trans temps, so the system is usually plumbed into the cool passenger-side tank.
In this case, the engine oil cooler is plumbed in to the cool tank, which would indicate GM knew that, while the engine oil required extra cooling, the 6.2L would not generate enough heat to damage the auto trans.
(This system cost me a PMD\FSD after installing the 6.5TD)

As a side note, the Buick Grand National 3.8L turbo V6 cars had the engine oil cooler in the back-side of the cool tank, and the auto trans cooler in the front-side.

At some point in the '80s, GM connected a tap on the thermostat housing to the tap on the water pump, to stabilize coolant temps by constantly recirculating coolant thru the engine, even when the tstat opened. This prevented hot-spots at several points in the block and heads.

It also permitted quicker coolant warmup, and maintained warm-up in cold weather.

For the 6.5L the tstat housing was rotated axially 90deg, orienting the tstat to the vertical plane. A new tstat was designed with an extension which, as the tstat opened, closed the bypass outlet, such that only radiator-cooled water was pumped thru the engine. The engine oil cooler was plumbed external to the radiator. The turbo engine generated much more heat than its non-turbo counterparts.

The system was still not efficient at dissipating engine heat, so the thermostat housing was again re-designed in '97, using the non-valved constant-bypass, but with two parallel thermostats to quickly dump heated coolant. The water pump was also re-designed with greater pumping capacity.

All the '80s and '90s trucks utilized the same heater plumbing - water cross-over to heater, heater to radiator cool side. It is part of the tstat-bypass constant-recirculation system.

So..your truck is standard shift, with an external engine oil cooler. You have a new 195deg tstat, the heater hoses are connected correctly.

The big Diesel radiator, with the engine oil cooler in the cool tank, and the tstat bypass connected, would be the best solution.
If that's not an option, then try, as you suggested, connecting the heater-to-radiator hose to the water pump tap. This may cause too much heat in the cab during the summer months, but do not install a block-off valve for this hookup.
The cooling system requires recirculation when the tstat is closed.

jd