Heating probs...changed stat twice, still runs cool

[dyno]

I am having problems getting my motor hot after doing a frame off on my 80 K20. The engine temp gauge reads just a bit above cold and the heater blows luke warm air. During the build, I put in a new heater core and rebuilt the top end of the 350. Checked all heater controls, all working properly. I tried changing the stat out again with a 195 degree one and still have the same problem. Yes, the stat is in the right way.

[pig rig]

try putting a new radiator cap on it might be bleeding off and not letting it pressure up

[Clyde65]

get a thermometer and start the truck in the garage or somewhere safe where you can open the rad cap and stick the thermo in there, watch to see the thermostat open and note what your thermometer says. You will know more when it opens or dont. I would also change the cap to a good one too.

stat could also be stuck open. why 195? I would go somewhere around 160-180 tops.

[jablack]

Make sure it's full of coolant..

[dyno]

10-4 guys...will try suggestions and get back to ya.

[INSIDIOUS '86]

What kind of fan do you have?
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[dyno]

It's the stock steel fan. Everything worked great before the restoration. Used same radiator but changed the heater core.

[sandorjoben]

I had a similar problem with my V15 a month or so ago, if you replaced the heater core, was it aluminum vs. copper?

I installed my replacement heater core(Aluminum chinese aftermarket model) and had to pull it all out again after the first test run because the weather stripping included to seal off the area around the replacement core was inadequate to block the gaps around the core itself when attached to the black heater box. Cold air was getting around the heater core because the cooling fins on the replacement were packed tighter than on the original copper core. Adding alot more adhesive backed foam weather stripping around the core ensuring a complete seal fixed the lukewarm heat issue for me.

As far as the low temp registering on your gauge, have you checked for a proper ground on the temp sender, not on the wire, but on the actual sender itself?

Dave

[dyno]

OK...stuck a good thermometer in the radiator, ran it for 20 minutes and maxed out at 147 degrees. This is the second 195 degree stat I've tried. I can't figure out why the stat won't close and bring the motor up to temp. Could there be air trapped in the system?

[old Rusty C10]

if im reading your post correctly then there is a problem with your thermostat. It is suppoused to remain closed until the motor reaches 195 degrees THEN its suppoused to open. If it is wide open at 147 degrees than its defective..Ive seen several from one parts store same brand all be defective try one from another store and brand maybe the springs are bad in a certain lot number of them

[dyno]

Originally Posted by old Rusty C10

if im reading your post correctly then there is a problem with your thermostat. It is suppoused to remain closed until the motor reaches 195 degrees THEN its suppoused to open. If it is wide open at 147 degrees than its defective..Ive seen several from one parts store same brand all be defective try one from another store and brand maybe the springs are bad in a certain lot number of them

Yep...I'll swap it out again and get back to ya'll.

[sierra4x4]

I had this same problem 2 years ago on my 86 4x4 with a 250. I put in a new Stant 205 thermostat and I had very little heat so I replaced the heater core and still little heat. I thought I had a dud thermostat so I put in another new Stant 205 thermostat and I still had the same problem so I used a thermometer and checked my coolant temp and it was only 140 degrees. Then I bought a Stant Superstat 195 and now I have awsome heat and it always runs around 200 degrees. So basically I bought 2 dud thermostats in a row.

[spudz]

thats why i hate aftermarket t-stats.. Ive MAYBE had 60% luck with them. It got to the point I wont even install them at work. I tell customers up front that I wont use them, or aftermarket electric fuel pumps. i'm sure there are good aftermarket brands out there but I know OE works so thats what I use.

[INSIDIOUS '86]

You can buy a balanced thermostat from moroso I run one in all my vehicles and never had probs
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[dyno]

Revisiting the low temp problem again now that winter is coming on....swapped out the stat with another brand of 195 degree (THIRD STAT), still maxes out at 145 degrees with a thermometer in the radiator. Put it in a pan of boiling water and it looks to open at 195. What the hell.

[INSIDIOUS '86]

I'm having the same issue with my 400 now. Never used to do this. I qualified my gauge and its accurate. Mine won't get past 140*. I'm going to play around with heater hose routing though. I can block off 75% of the rad to get it to temp but if its sits for to long it will get past 200*

[dyno]

Originally Posted by INSIDIOUS '86

I'm having the same issue with my 400 now. Never used to do this. I qualified my gauge and its accurate. Mine won't get past 140*. I'm going to play around with heater hose routing though. I can block off 75% of the rad to get it to temp but if its sits for to long it will get past 200*

I never thought of the heater hose routing. I didn't think it made a difference which hose went where. Could they be backwards?

[motornut]

I watch the gauge and see my gauge rise and fall,till it stays open.
what is your ratio mixed at?
wind chill?
the rad loses more heat in the cooler air temps,why i run with a cover
i try to run the core from the intake to pump,not intake to rad

[INSIDIOUS '86]

Originally Posted by motornut

I watch the gauge and see my gauge rise and fall,till it stays open.
what is your ratio mixed at?
wind chill?
the rad loses more heat in the cooler air temps,why i run with a cover
i try to run the core from the intake to pump,not intake to rad

That's what in going to do. This summer it did the same. It would hit 160* if I idled long enough but went down when I drove.

[Sabaka454]

Ho do you have the bypass circuit routed. Can you post pics of the hose routing?

[smashingchuck]

My suburban has run like this for years. I've tried a couple different stats, two heater cores, two radiators... surprisingly the heat is pretty hot. I may try an oem stat and see if that fixes it.

[chengny]

still maxes out at 145 degrees with a thermometer in the radiator.

Unless I am misunderstanding - or you have something other than a stock style radiator - you are checking the coolant temperature at the radiator cap throat.

That is the outlet side of the radiator. Your probe is measuring the temperature of the coolant after it has passed through the heat exchanger.

Depending on ambient temperature (cleanliness of the radiator watersides, fan capacity, etc) a 50 degree delta T (temperature drop) would be expected at the flow rate of the coolant during idling conditions.

So if you are getting 145 -150 outlet temperature - and assume 50 degrees of sub-cooling - radiator inlet temperature would be about 195 - 200.

That inlet temperature would coincide almost exactly with the thermostat's 195 degree rating.


Same basic concept here:

i try to run the core from the intake to pump,not intake to rad

If the coolant leaving the heater core is returned to the main part of the system at the radiator's outlet tank - it will not be subjected to any further cooling. It just leaves the outlet tank, flows through the lower radiator hose/water pump and then is returned to the coolant passages within the block. There may be a slight loss of heat as that coolant passes through the lower radiator hose but not enough to affect the overall system temperature.

Location of the temperature sender (and consequently what is indicated on the dash thermometer) is important too. Normally the sender for dash indication is screwed into the cylinder head between #1 & 3. But there is another tapped bore between # 6 & 8. If the sender is located at that point (between 6 & 8), dash indication will be considerably lower. This is due to the fact that, a SBC engine has no rear opening from the cylinder head cooling passages into the intake manifold. This feature forces all coolant to traverse the length of the head. It can only enter the intake manifold coolant passages at the front end of the heads. It follows that, as the coolant makes it's way from front to back of the head it continues to pick up additional heat. So if coolant temperature is measured at the rear of the head it would be expected to show as much cooler.

[motornut]

Originally Posted by Sabaka454

Ho do you have the bypass circuit routed. Can you post pics of the hose routing?

me:
the orange block is for winter
blue is summer

[kikkegek]

I agree with Chengny on a lot of stuff...I just dont think a radiator will cool 50K during Idle...not even with a double electric fan setup on a double row alu radiator.

you do have to measure the engine temp at the thermostaat housing using a infrared thermometer preferably. I use a small cheap ir thermometer to measure my temp on the thermostaathouse.

this one, except I got it in white:
http://www.amazon.com/Oakton-WD-39642-00-TempTestr...
but lets see some engine bay pictures first before we jump to conclusions.