lack of temp

[86c20]

ok so as some know i have been on the hunt for heat in my truck. started with a new rad as it sprung a leak went with the big gas rad 4 core. then it was a a new core as that had a hole from a few years ago. still no heat bad tstat ok fine new tstat still no heat box was not on right. fix that get some not alot. found water pump to be on the way out bad bearing. replace that have lots of flow still not much for temps out the core or motor. put in new 195 after finding that the tstat houseing was only 140 lines to core where 125 and the rad inlet was 120 out was 90. rad cap even at temp is cold to touch. after let truck run for 30 min get heat everything seems hot run down road less the n5 min back to cold. i am at a loss here. also i have 3/4 of the rad blocked off with cardbord to try to get temps up seems to make zero diff in anything at all.

[rich weyand]

You're getting what out there on the island, highs in the low 30s? The SBCs run cold, unlike their BBC cousins. In the winter, you have to take extra measures to get the heat up, especially with a four-core radiator. Block off the whole radiator with cardboard for a drive around and see what you get.

[86c20]

yea its been cold but still even the warmer days she dont get hot. will block it all off see what happens.

[Bigstevex4]

ya bgger isnt always better my boss who always goes with cheapest possible part. we have 2 core rad. in 7.3 fords transit busses running 2 A/C units in 100 degree weather and no heating problems. i put card board in front 1 core on my 6 cyl c10 .

[homemade87]

Sounds like the blend ( hot/cold ) door in the heater box is not closing all the way .

[Bigstevex4]

Originally Posted by homemade87

Sounds like the blend ( hot/cold ) door in the heater box is not closing all the way .

I wired mine and the heat door to fuul heat

[homemade87]

Originally Posted by Bigstevex4

I wired mine and the heat door to fuul heat

From everything you have done I would say the heater core is stopped up . Could be worth a try to back blush it with a hose and see how it does .

[86c20]

core is new and flows great. i left the water low to see how it was doing.

i will check the heat do is going to full hot
as for the rad i thought what i had was the big one i was wrong. the orginal was small then that died years ago and my friend gave me a use one that was for v8 and it was bigger then the first and thsis on is bigger then that lol.

[tucsonjwt]

I assume that you have felt the heater hoses going into/out of the heater and determined that they are not warm?

[chengny]

The (low) quantity of BTU's being extracted from the heater core - and delivered into the cab - is most likely just a symptom of a larger issue. A HC inlet and outlet temperature of 125 degrees lower than design, but should still result in at least warm air at the vents.

A heater core with obstructed/fouled watersides will manifest itself by having a higher -not lower - delta T (i.e temperature drop) as measured at the inlet and outlet piping. This is due to reduced coolant flow rates (while the cold air flow remains constant). If you can feel a huge difference in the temperature of the heater hoses - that indicates a low flow of coolant through the HC tubes.

The fact that your inlet and return hoses are close to the same temperature would be cause to eliminate the core as the problem. Also you don't mention any lack of air flow volume at the vents, so that would eliminate a low heat exchange rate due to debris on the fins.

So, assuming no unusual outside factors (your ignition timing is not extremely over-retarded, you do not have a way oversized oil cooler installed and your fan clutch is not locking up prematurely, etc.) - it would be safe to assume that your engine coolant is being prevented from reaching operating temperature by leakage either through or around the t-stat. The following statement would tend to support that theory:

after let truck run for 30 min get heat everything seems hot run down road less the n5 min back to cold.

With the truck at idle, the water pump's impeller is turning slowly and very little discharge head is developed (like any other centrifugal pump). It is acting more like a circulator - just kind of pushing some coolant along. But when you take it out on the highway, engine RPM increases- and the impeller spins up - the pump starts to develop some discharge pressure.

If the t-stat does not have a tight seal around it's opening in the intake manifold (or the valve itself does not fully shut when cold), this creates a path for unrestricted flow past it. This may not present a huge problem at idle speeds, but at higher engine RPM's it disrupts the proper operation of the cooling system. The pressure developed by the water pump can prematurely force coolant (i.e before it has warmed up) out of the manifold, through the upper radiator hose and down into the heat exchanger section of the radiator.

With your engine stone cold and the radiator cap removed from the outlet tank, bring the revs up to somewhere near what would be expected at cruising speed. Look down into the outlet tank and observe the flow of coolant issuing from the ends of the tubes (this will require temporarily dropping the coolant level - just enough so you can see the ends of the top few banks of cross-tubes).

With the engine cold - and the coolant well below normal operating temperature - the thermostat should be closed. You should not see any flow into the outlet tank of the radiator from the tube ends (only what could pass through the vent hole in the t-stat).

Another way to do this test is to pull the upper radiator hose off the inlet tank neck and check for a flow out of the hose end.

[Dead Parrot]

Do not assume that a new thermostat is a good thermostat! I am on #3 in about as many months. Both previous t-stats started out showing good by the temp gauge, then after a couple of weeks, the temps would start varying from too cold to too hot. When they pegged at too hot, swapped in the next one. Put in new one, temps go back to correct for a bit. Current brand is a Stant. So far, it is behaving.

If your HC return goes to the water pump, consider moving it to the radiator if your radiator has a hole for it. The main reason for this is it makes it easy to visually verify good water flow. And it is easy to stick a meat thermometer in the return flow to see what the real temp is.

Make sure your AC compressor isn't running. It will on defrost and bi-level. Nothing like dueling climate control systems when trying to diagnose a problem.

[86c20]

no ac sadly but its on the list for......somepoint when i have money lol.

the return is in the rad not the pump.

i seem to have good air flow but i will be up grading the fan at some point belive that the newer fans move more??? any clue what i should look for?

i have been playing with the timing as i have come to a detonation problem wrong plugs timing has always been off in the truck but still pings a bit.

no oil cooler

the fan clutch in this truck i have never once heard it in the 8 years of having her. but i was thinking that also. what is the best way to check if its locked on?

does anyone know what the temps in to the rad should be and at the houseing? also the line in to the core? trying to see if i can point in a better direction

[Dead Parrot]

Fan clutch check - with the engine OFF, if you can move the fan with one finger, not locked up. I rarely hear mine kick in, even in 100+ summer temps. If it isn't overheating, don't worry too much about it.

On the timing - make sure your mechanical advance isn't sticking on full advance. I know from experience that a sticking advance, especially one that sticks intermittently, makes timing a PITA.

Since the return is in the radiator, have you visually verified good coolant flow thru the heater core? May be low at idle, but shouldn't take much speed up to get a good flow.

[86c20]

ok update time. i have better heat. i am getting about 120 out of the defrost vent.

i ran down the list of things you guys gave me. checked fan still good. rechecked tstat and tstat bypass. good. so i went back to the bord and came up with the new rad is too damn big. bigger pice of card bord orver 75% now i have 180 at the tstat and 120 vent temps. yet to drive it around town to see how she does but sitting in the drive way on a 50* day for an hour she stayed at 180. i know the highway will be a diff story and so will spring. i may brake down and get a smaller rad.time will tell. thanks guys

[rich weyand]

On the highway it will run cooler. Ram air through the radiator will be much more flow than the fan can deliver.

You might consider an electric fan setup. It just stays off unless you need it. I have a write-up floating around on the net somewhere about what I did. Just google my last name and electric fan.

[donut]

Other thing to try is blocking more of the rad. My K-20 ran cool even with 80-85% covered. The only spot not covered was the aux tranny cooler.

[86c20]

the only spot open right now is right whee the inlet is seems to hold right at 180 and that is just how the card bord lined up lol. time will tell. i am thinking i might get a smaller rad in time back down to what i had. i still have the old one too.

i do like electric fans and want to swap to them in time.

thanks guys

[hatzie]

I wouldn't replace the radiator.
There are a couple cheap things that can be done besides a radiator/grille bra that can increase the heater output.
180 degrees F is a cold thermostat. If you aren't overheating there's no reason to not run a hotter thermostat. Stant makes a 195 degree F thermostat you can get for around $7.
Moving the heater hose from the radiator to the engine will help.
If you're cooling too much while not moving the fan clutch is probably in need of replacing.

[86c20]

hatzie the tstate is a 195. the intake right under the houseing is reading 180 with a temp gun and the gauge in the truck is on the line before 210 witch i think???? is 180 to 190ish seems know one is sure on that that i have read. i do have a 205 stat that i am thinking of trying. just dont like to go to hot thats all.

[rich weyand]

195 is the right thermostat.

I run an electric fan which is thermostatically controlled, and I block the portion of the grill in front of the radiator opening in the winter to block ram air from the radiator. Prior to those changes, I had little heat in the winter. And together with the large gap between the defrost Y-tube and the heat box, forget about defrost.

Now, I have excellent heat and defrost. She reaches operating temp even in the coldest weather. With my ungraduated '78 temp gauge, and the correct sender, the temp needle points straight up at the middle tick on the gauge at operating temp.

I used a fender protector to block the grill:

[hatzie]

Originally Posted by 86c20

hatzie the tstate is a 195. the intake right under the houseing is reading 180 with a temp gun and the gauge in the truck is on the line before 210 witch i think???? is 180 to 190ish seems know one is sure on that that i have read. i do have a 205 stat that i am thinking of trying. just dont like to go to hot thats all.

If she is running 15 degrees under the thermostat open temp I doubt you'll have an issue with a Stant 13352 205 degree thermostat. It'll probably be just fine year round in Massachusetts especially out on the island.
Thermostats actually start to open below the rated temp with full open at the rated temp.
That being said... I never had an issue with 350 or 305 giving me enough heat in several different trucks when everything was right. My 75 & 85 would drive me out of the cab on high. Several of them had the biggest 4 row radiators I could buy... including those two. They all had good clutch fans and at least 195 degree thermostats. Low engine temp is usually a bad fan clutch or weak T-stat. Low heat is usually a leaky blend door.

[86c20]

when do they start to close? and the last 2 dont seem to close up once open.

more then likely i will put it in in the am after the dentest with the wife. she is haveing a tooth or 2 pulled we hope. so i should be able to work in peace lol

[hatzie]

http://files.engineering.com/downloa..._operation.doc
The guy quoted in the above doc explains some about thermostat temp curves.
Apparently they are not published because the temp curves are "proprietary information". Heaven forbid the Schmoes actually have enough info to make an informed decision... more like find out they are peddling sub standard parts for the application that don't meet factory specs.
Just like the aftermarket temp senders that don't quite match the GM Temp~to~Ohm curve.

[86c20]

i want to say that guy is a straight up bs guy for some comp. cant say what the curves are or that going to a 195 over a 180 will really make it hotter???? i mean that seems dumb. would you want to have a sbc stat that will hit what ever and hold it around this or that? makes no sense to me but i am just low man on the pole. have to see what i can find.

[hatzie]

Just a thought but worth asking...
Are you running an absoloutely known 50:50 Glycol:H20 mix? Or is it more like 70:30 or 60:40?
I've had problems getting up to temp on vehicles the prior owner screwed up the anti-freeze mix percentages by topping off with straight Glycol. I dumped the cooling system and poured in 50:50 that I mix up in 4 gallon lots using good old fashioned Prestone Green and distilled water.