2nd Gen Non-Engine/Transmission Heater core question

[BoeingDiesel]

I recently replaced the heater core on my ’99 and up until now I didn’t realize coolant continually flows through it. I just presumed the flow was controlled by electric actuated solenoid valve. Is this a necessary feature that adds to engine cooling or for some other purpose?
It would be simple enough to install a 3 valve bypass system…any thoughts?
BTW, now that I'm retired I decided to do the change out myself and it wasn't quite as nasty as I thought it would be.
Thanks
g

 

[NIsaacs]

I think the heater core flow is a necessary evil despite the heat transferred to the AC system. I think the heater core is the only bypass for the cooling system so I would not shut it off. The older 12 valves had a built in bypass in the thermostat housing that I don't think the 24v has.

Nick

 

[klcammie]

Part of the reason that it flows is so you can regulate the temp of the A/C. It is a blend air system. The HVAC uses a blend air door it the box, it blends the warm air and cold to get the temp you want. Also if you are using an oem thermostat there is a hole with a jiggle pin for a bypass.

 

[BoeingDiesel]

I understand both of your comments and that's why I was thinking of constructing a bypass manifold that would in normal setting direct the coolant through the core and bypass would loop the coolant back into the block. I don't ever recall throttling back the A/C but I see your point. What brought this up was after I installed the new core and test drove the truck I still hadn't put the glove box back in and reaching up into the housing it was hotter than H.

thanks all I appreciate it
g

 

[RBeard]

I just changed mine and I was surprised that the top of the core is not covered like the A/C coil. I'm going to pack insulation around it before I reinstall the glove box.

 

[GAmes]

The older 12 valves had a built in bypass in the thermostat housing that I don't think the 24v has.

That is not accurate. 12 valves have a jiggle pin that will bleed air from the cooling system when the engine is not running. When the engine is running the jiggle pin is closed.

 

[NIsaacs]

Gary, the 12v does have a bypass system in the thermostat housing, see illustration D and read line D.

Nick

 

[NIsaacs]

Here is a pic and description of a Napa 12V t-stat. Note the flange at the bottom for the bypass.

Nickhttp://www.napaonline.com/Catalog/CatalogItemDetail.aspx/Thermostat-Regular/_/R-THM370180_0293171750

 

[NIsaacs]

After a little more research it appears the 24v also has a bypass system built in.

http://www.napaonline.com/Catalog/CatalogItemDetail.aspx/Thermostat-Regular/_/R-THM375190_0293170922

Nick

 

[GAmes]

Gary, the 12v does have a bypass system in the thermostat housing, see illustration D and read line D.

Nick

Just like any most other engines, if the thermostat doesn't open the coolant routes to the water pump and recirculates through the engine. That includes the heater hoses and is why we get heat before the t-stat opens. With the 12 valve that is "via internal drillings in the block and cylinder head". Regardless of exactly where the bypass is located, it has nothing to do with the coolant being continually pumped through the heater core, which is what I was referring to.

 

[GReed]

I put ball valves in both of the heater hoses. I block off the heater during the summer. On 100deg days, the AC really cools things down. I've read it lowers the AC about 15deg. I believe it. No problems with overheating, even towing 5th wheel over mountain passes. I open the valves for a day or two once or twice a month to flush stale coolant out of the heater.

 

[NIsaacs]

and that's why I was thinking of constructing a bypass manifold that would in normal setting direct the coolant through the core and bypass would loop the coolant back into the block.
g

I would think this would work just fine and like GReed said, help the marginal AC keep up on hot days. I would be afraid to not bypass the coolant like he did thou.

Cummins rates these engines at 2500 rpm, with the water pump rpm/flow designed around that speed. Then Dodge ups that to 3k+ rpm and puts the flow/pressure at the raged edge of safety. I have seen a lot of head gaskets seep water at the right front corner. The water jacket is real close to the edge so the gasket printed seal is only about 1/8" wide at that point, I blame excess pressure. Also Dodge truck heater cores seem to leak more than other trucks, even soft plugs can blow out.....

Nick

 

[BoeingDiesel]

I would think this would work just fine and like GReed said, help the marginal AC keep up on hot days. I would be afraid to not bypass the coolant like he did thou.

Cummins rates these engines at 2500 rpm, with the water pump rpm/flow designed around that speed. Then Dodge ups that to 3k+ rpm and puts the flow/pressure at the raged edge of safety. I have seen a lot of head gaskets seep water at the right front corner. The water jacket is real close to the edge so the gasket printed seal is only about 1/8" wide at that point, I blame excess pressure. Also Dodge truck heater cores seem to leak more than other trucks, even soft plugs can blow out.....

Nick

Yep, I agree. I'll post some pics' when I make up the manifold.
Thanks All and have a very Happy Thanks Giving!
gregg

 

[SAndreasen]

Part of the reason that it flows is so you can regulate the temp of the A/C. It is a blend air system. The HVAC uses a blend air door it the box, it blends the warm air and cold to get the temp you want. Also if you are using an oem thermostat there is a hole with a jiggle pin for a bypass.

So if the stupid door was gone I could actually get full heat?

 

[klcammie]

Maybe????? The way I remember it the incoming air passes thru the a/c condenser then the pass the blend air door. Which means if there is any cold in the condenser (like when you run the defrost) your air is not full heat.

 

[GAmes]

So if the stupid door was gone I could actually get full heat?

No, then you would get little to no heat. The door routes the entire air flow over the heater core using the door when you turn the knob fully clockwise. Operation of the HVAC starts on page 24-1 of the factory service manual. If your 12 valve has an OEM t-stat you can disregard the comment about the jiggle pin. Ours is located elsewhere, but either way it's only function is allow air to escape the engine and is closed when the engine is running.

You can also bomb your system so that the AC does not come on when you turn the mode control knob to the defrost position. http://dodgeram.org/tech/repair/HVAC/Defrost_AC.htm

 

[SAndreasen]

The ac also comes on in the floor and vent setting on the knob as well . I'm tired of having no heat my 92 with no door panels and a custom hole in the floor was warmer than this thing

 

[Matt42]

I put ball valves in both of the heater hoses. I block off the heater during the summer. On 100deg days, the AC really cools things down. I've read it lowers the AC about 15deg. I believe it. No problems with overheating, even towing 5th wheel over mountain passes. I open the valves for a day or two once or twice a month to flush stale coolant out of the heater.

I do something similar, but without the ball valves and no pretense whatsoever at finesse. I soldered up a U shaped fitting out of 1/2 inch nominal copper pipe, using repair sleeves (copper sweat couplings also work) where they enter the heater hoses coming from the engine. I wrapped three wraps of 22 gauge stranded copper wire around the repair sleeves and just sweated solder onto them to act as retainer bumps behind the hose clamps. Then I clamped the U fitting in place so it just returns the coolant back instead of sending it through the heater core. I capped off the heater core using plugged heater hoses to keep out dust and bugs. When our 117 degree summers are over, I flush out the heater core, reconnect the heater hoses and store the fitting until the next year. Doing this makes a noticeable difference in the interior temperature.