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heat not hot in 98 dodge ram

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Jan 7, 2010, 9:53 AM

Post #1 of 8 (13263 views)
heat not hot in 98 dodge ram Sign In

1998 Dodge Ram 1500 Quad Cab
360ci/5.9L vin code Z
241000+ miles
repairs done in its life:
3 water pumps most recent 2006
radiator replaced sept 09
torque converter rebuilt at 235900 miles
fuel pump replaced june 09
rear end regeared may 07
timing chain and lifters 07
all front end susp. parts replace may 07
the rest was norm maintance stuff brakes, plugs, hoses, belts ect.

I live in Myrtle Beach SC, USA and the winters here are not usually cold (30's at night and 50's in the day) but this year is the exception year.(nights in the teens and days in the low 30's).
The past 4 winters I have not needed the heat much so I dont know how long I have had this problem but up until moving here (dec 05) the heater would run you out it was so hot. also I have always had a 180 degree t-stat as required by my performance programer that was installed in 2002.

okay here is the scenario.. heat selected wide open hot. when the fan is on low it feels hot from the vents. when the fan is turned up on high the air cools signifacantly. I drive 40 minutes to work at 45-50 mph engine tach reads around 1500rpm. Mostly open road very few traffic lights. my truck stays in a garage so the commute to work is warmer than home. My truck sits outdoors all day in a shaded parking lot so it is colder at 6pm than at 10 am.

what I have done so far is warmed it up and felt the hoses. the heater core input hose is warmer by touch the the hose from the heater core almost like a partial restriction. I removed the heater hoses from the water pump and attached my garden hose to each hose one at a time and flushed and back flushed into a bucket to check for obstructions. none found. clear water/antifreeze was all that came out. I use a 50/50 mixture and have always used same brand and mixture. Raditor has been flushed and new antifreeze every 2 years.

The temp guage works correctly and it reads approximately 180 - 190 all the time after the tsat opens. The water temp was checked with a thermometer in the neck to calibrate the guage on the dash and it was only a few degrees off. I ruled out the tsat.

The heat selector knob seems to work correctly when moved to the cold position it gets really cold and all summer the a/c blew ice chunks so I ruled that out.

What do I do next ? the service book I have dosent give me anything to do except change the heater core if it leaks and it dosent.

sorry the post is so long but I tried to give as much information as possible.

Veteran / Moderator

Jan 7, 2010, 11:28 AM

Post #2 of 8 (13217 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In

I would try a couple of things.
First put an OE thermostat in, rated at the manufactures spec; your performance up-grade may want the colder stat but the heater is designed for likely a 195 degree. If you feel you need the colder stat switch it out come spring?
Next flush out the block at the heater core spigots; making sure there’s no restriction to or from the spigot.

One other thought; on some OE intake manifold gasket, may have had restrictor plates to partially cover one or more of the coolant passageways. This was to force coolant to flow in a certain direction and to slow the coolant down while passing through the cylinder heads. These restrictors were made of thin tin and would rot out; allowing the coolant to flow as it pleased. Maybe check at the dealer; to see if their gasket has these; some after market gaskets may not?

Canadian "EH"

(This post was edited by DanD on Jan 7, 2010, 11:42 AM)


Jan 7, 2010, 12:32 PM

Post #3 of 8 (13207 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In

okay I can change the tstat easily enough and I will try that 1st.

the inlet line of the heater core comes off the block and it is the hotter of the 2 lines. the cooler of the 2 lines is the return line and it goes to the water pump. Do I flush into the block line and where does it come out? should I remove the return line to the radiator and catch it there ?

as far as the intake gasket when I replaced the lifters I used Felpro blue gaskets. I dont remember any restrictions that were tin or any kind of metal. does this matter? or by installing Felpro gaskets is this nolonger a possibility?

if the factory restricted the water flow would installing a gate valve that I could adjust in the line be any benefit to me. if so which line would work best?

thanks for you input sofar and I will pick up a hotter tstat today.

Veteran / Moderator

Jan 7, 2010, 1:42 PM

Post #4 of 8 (13202 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In

Just blow water into both the feed and return engine spigots to make sure there are no restrictions; who cares where it comes out?
The intake gasket was just a thought and I’m not sure your engine’s intake gasket had them or not; that’s why I mentioned checking an OE gasket? These internal restriction would force/redirect coolant and possibly into the heater core?
No putting a valve in the heater hoses would only restrict the amount of coolant that could get to the heater core; we need more. Why I think that is because you said on low fan it feels hot; but on high it cools; not enough hot coolant to keep the core hot.


Canadian "EH"


Jan 7, 2010, 3:50 PM

Post #5 of 8 (13198 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In

okay I picked up a 195 degree tstat and as soon as the engine cools off tonight I am going to change it. maybe that will be all it needs at least the water will be 15 degrees hotter. so I will try flushing the block out when I have it apart again..
tomorrows high will be upper 20's , brrrrrrrr....... thanks for your help. i'll be back tomorrow.

Veteran / Moderator

Jan 7, 2010, 4:30 PM

Post #6 of 8 (13197 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In

Upper 20’s that’s dam near T-shirt weather for us; our high today was 15 degrees. LOL


Canadian "EH"


Jan 7, 2010, 9:25 PM

Post #7 of 8 (13186 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In

Brrrrrr. I knew I lived in the south for some reason :0)


Jan 9, 2010, 6:14 AM

Post #8 of 8 (13183 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In

okay I changed the tstat and flushed the block. its better but not right. the heat is hotter probally only 15 degrees since the tstat is 15 degrees hotter. it still cools off when I turn the fan speed up. I have also noticed that it is hotter at 2000 rpm that 1500. I can feel the air heat up during acceleration and cool down during decelleration and especially at idle. All this happens with the fan on higher speeds. I do not notice any heat change when the fan is on low.


heat not hot in 98 dodge ram

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