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Re: heat not hot in 98 dodge ram

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Jan 20, 2010, 12:15 PM

Post #1 of 13 (4955 views)
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I have a very similar story. I have a 1998 Dodge Ram 1500 360ci with 170,000ish miles on it. I had the radiator go out on me on our fist really cold day of the winter (high in the teens). The radiator had separated where the core attaches to the plastic sides. I replaced the just the radiator as I was doing it in the drive-way and it was reasonably cold out. Very straight forward, remove the shroud, pull the hoses & trans lines, replace.
After that I was never able to get any heat in the cab (it had worked very well before). I could see the temperature gauge rise to about 200°F and then fall to around 170°/160°F and never get much past 190°F or so. I felt fairly confident that the thermostat was working as it should.. but it never really got hot inside that cab. Several weeks went by and no change. I went out to a buddy’s when we could pull it into his garage and look at it. We felt the lower radiator hose and it was cold (it’s a 30 min drive at 50mph to his place but it’s also 12 °F outside) but the top one was hot. We let the truck cool and pulled the radiator cap and let it run until after I saw the temperature gauge peek then fall to a constant temperature. We didn’t see very much circulation in the radiator. We then let it cool down again and pulled the top hose and let it run with the top hose in a bucket… when the thermostat opened we saw very little coolant come out the top hose and mostly some steam. From this we concluded that the water pump had failed.
We replaced the pump (prior to loosing the pump we did see evidence of coolant leaking on the harmonic balancer). I saw immediate improvement in the heat inside the cab, while we were refilling the system with coolant. On the drive home it was not as hot in the cab but I figured that there was still some air in the system that needed to get worked out. The following day I noticed that the coolant reservoir was low and I toped it off.. this happened twice over the following week but has been steady at the ‘Full’ line every since. I still do not have the heat in the cab as I did before the radiator failed. Do I go ahead and replace the thermostat even though it seems to be operating correctly? I also was wondering if you were able to fix the problem that you were having?

Thanks Eric

please note that this is in reply/response to:;t=search_engine originally posted by skydver
I am not sure why it didn’t thread

(This post was edited by ebrady on Jan 20, 2010, 3:45 PM)


Jan 20, 2010, 4:02 PM

Post #2 of 13 (4917 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In

I too had the radiator crack in the same spot. the replacement also cracked 2 days after install but the 3rd one seems good. I have not had a water pump that didnt pump. both hoses get hot and there are no engine cooling problems. At this time I only have 15 degree hotter heat. I have also had a friend (not a mechanic) tell me maybe I should replace the water pump. As of right now I havent decided to try that. The pump is pumping fine and not leaking. I dont understand why this would effect the heater. I get extremely hot air when the fan is on low 195 degrees to be exact. so I know the pump is doing its job. I might be wrong but I dont think that is the problem. I welcome any explannation as to why this would make a differece. when mornings are in the upper 30s and low 40s the heat works fine. its still slow to warm up but I do have to turn it down before I get to work. I have found that if I run the a/c on max(recirculate) and the temp selector on hot as possible then it will warm up on those 20 degree mornings. so on those rare days I will make do. I cant justify in this economy spending a hundred bucks on a water pump that I dont know beyond any doubt will fix the problem. So if you can explain why (or anybody reading this) I would love an explaination. good luck with yours.

Tom Greenleaf
Ultimate Carjunky / Moderator

Jan 20, 2010, 6:54 PM

Post #3 of 13 (4915 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In


I moved it because you tagged it on an old post such that we would have to read the whole thing again. State just your problems please as they are not "just like that one" that was a mile long.

Ok: You are messing with 12F temps so thermostat isn't going to open too much and lower hose would be cold as radiator has abundant cold air.

If the complaint is poor heat than be checking the heater hoses and that temp can get to operating temp, no more no less even at the cold temps. If it fluctuates, continues to have air that's an issue. At first fill there will be some air that should purge out in a couple cycles such then when radiator cap is removed it's always full. Recovery tank will vary level based on warm or cold as marked.

Need to know the heater core's hose temps in and out - the smaller (typical for inlet to be smaller hose) should be very hot and outlet still fairly hot on a cold day but still not cold - all with engine at operating temps.

What is the coolant freeze protection set to? Way too strong won't work well,

Long retired now


Jan 21, 2010, 8:36 AM

Post #4 of 13 (4899 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In

Thank you Tom & SkyDver.
I read your posts when I got home from running errands after work last night. I had an hour or so of drive time with 15 minutes of that being on the Interstate @60~70 mph. The outside temperature was 31° F (with a light rain) So somewhat warmer than what we have been having. I went out to check the heater hoses as Tom suggested. The truck had 15 or 20 minutes of cool-down time by the time I got out there. I was able to feel both heater hoses from as close to the water pump as I could get all the way to the firewall and they were both consistently warm to the touch. I also felt the top radiator hose and it felt about the same temperature as the heater hoses. The lower radiator hose was cold. I am not exactly sure how to specifically measure the temperature of the coolant in just the heater hoses. I do have several meet thermometers that I could shove in one of the vents in the cab while the heater is running and the truck is at operating temperature ((160°/170° F) per gauge). I am not sure if that will give an accurate reading of the actual temperature of the heating system.

Both heater hoses appear to be the same size inside the engine compartment.

(coolant freeze protection) - Fresh anti-freeze when I replaced the water pump.
Approximately a 60% solution of antifreeze. It was Prestone (non-diluted/all make & model )that I picked up from Wal-Mart.

Thanks -- Eric

Tom Greenleaf
Ultimate Carjunky / Moderator

Jan 21, 2010, 9:45 AM

Post #5 of 13 (4886 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In

Eric - sorry if I came across short on you. No excuse - was tired from shoveling damn snow and the phone was ringing off the hook messing up my train of thought. I'm here all the time so would know how the site works best for you.

Know this: You need to know a few things with a poor heat situation. Is the thermostat new or not staying shut till it's prescribed temp? If your gauge is accurate the answer is NO. 160-170F will only pant warm air. There's a temp loss just going thru ductwork that varies but can be significantly lower than the coolant that goes thru the core.

It's hard to understand but you are quickly losing heat transfer ability with strong antifreeze concentrations. As said it's a terrible heat exchanger as it holds less caloric value that plain water which we can't do. One huge problem is testers are frequently way off! I test new testers with exactly known 50/50 mix to achieve an industry standard of -34F protection. Some vehicle ask for -20F to enhance heat transfer for the engine! A setting of -20F at -40F will freeze to a slushy mess that won't circulate (a problem) but doesn't expand when frozen. Plain water expands as we know and wrecks things and has no anti corrosive ability so we still use antifreeze. Rock and hard place.

We really need know as you are complaining what the available temps really are. Radio Shack has a $15 touchless infrared thermometer which is wicked handy. You will love to have one - check you home fridge and freezer - oven temps etc.

Harbor freight (I hear) has one for $10 with the battery but range isn't as much.

The metal cover to the thermostat should be very close to the thermostat's rating once it has opened even a smide. Doesn't matter too much how cold the weather as there is abundant heat from and engine. Think of the wind chill on a radiator at hwy speeds which is the speed heat will transfer not when it will freeze.

The heater hoses when fan is on low should be hot to the touch - perhaps too hot to touch depending on your tolerance. I trust you will be careful as 200F water is way over what would burn you.

Air must be out and once drained it takes a couple or more cycles of thermostat opening and closing to finish getting air out in this type engine. Some are a nightmare to purge.

A test: Feel upper hose from cold. Duh upon start up it should be cold and stay stone cold till engine is up to operating temp and even though at cold temps thermostat doesn't open fully you can quickly notice that hose warm up. If it's showing warmth before the engine is warm something is wrong with the thermostat. It could be the part or it's installed with a bend or such that coolant can pass by it and even a little will mess up the show.

Need the actual temps available to proceed. Sounds so far like the heater core is ok but the coolant temp is too low and the higher fan speeds will act like wind chill on it but the higher calorie hot liquids win out over air even well below zero and especially a V8 engine. I'll allow for excuses at about -20 or more but temp should stay even in this at all but the wildest extremes if all is well.

Job #1 is accurate available temps of coolant and never mind the lower hose of radiator,

Long retired now


Jan 21, 2010, 2:45 PM

Post #6 of 13 (4875 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In

Thank you Tom!
I looked on line at Radio Shack ( but they were not showing any. Harbor Freight does have one for $20.00 ( and we do have a store relativity close by, but I won't be able to get out that way until this weekend. I did try and call a couple of the auto parts stores close by (O'Riley & AutoZone) to see if they had one behind the counter that I could borrow right quick to take the mesurments out in the parking lot, but neither one of them had one. I should be able to do your quick test tonight or late tomorrow after noon. I have NOT replaced the thermostat as of yet. I hope that the quick test can rule one way or another on weather to replace it or not. I would think that the air has purged it's self from the system as I have been driving it daily (Sat=2weeks on new water pump). With the cold we have been having I do let it warm up out in the drive a good 10~15 minutes before I leave in the morning.

Thank you again for your help and I will let you know what the results are.

-- Eric

Tom Greenleaf
Ultimate Carjunky / Moderator

Jan 21, 2010, 3:26 PM

Post #7 of 13 (4869 views)
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that's the one I use and they may have quit selling them. They should be available at other stores - automotive or not. Fooled with the meat thermo types and household in/out wired ones no really suitable for this.

I know you don't want to wait forever but just Googled Images which leads to places and Amazon had a small one and many places but didn't dig into prices. Ask and ye shall find one out there,

Long retired now


Jan 22, 2010, 10:50 PM

Post #8 of 13 (4839 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In

The wife and I were out by Sears so I just went ahead and picked up an IR Thermometer (-4° to 500°).
Here are the numbers:

Heater hose as close to the fire wall as I could get (~4” from hose to meter)
· IN: 150°
· OUT: 127°
· Upper Radiator hose: 140° (as close as I could get to the water neck)

It’s a balmy 34° out according to

The truck was cold since we took the wife’s car out shopping. I did the best I could to run back and forth from checking the gauge in the cab and the upper radiator hose. The hose stayed right around 38° until the gauge got to about 195° and then began to increase in temperature fairly quickly. Based on what you said earlier, it sounds like the thermostat is fine?
I did measure the reservoirs on either side of the radiator and was surprised that the intake said 152° and the outgoing was 41°. That just seem like a big difference, but then I am not the expert.

Oh and one more thing… you were right I have been measuring everything… but then got spacious when it said my beer can was 66°…until I read the manual and it said that reflective surfaces would not register correctly. Whew I was about ready to take the darn thing back. Tongue


Tom Greenleaf
Ultimate Carjunky / Moderator

Jan 23, 2010, 4:14 AM

Post #9 of 13 (4826 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In

Cool Beans - didn't know Sears sold them!

As said there's a drop in output air temp just going thru the dash duct-work so you probable only get 140ish F outputs in cab. Home forced hot (so called) air is about that so it doesn't burn anything but comes in copious amounts. Motor vehicles exchange cabin air for fresh roughly every 40 seconds and when moving along there's a lot of wind chill on cabins that are not really insulated like a home heat.

You don't have enough heat available. The thermostat must be opening too soon or leaking a bit past it all the time.

That's a pic of Mopar small block which probably hasn't changed basic format. Vertical thermostats if new can slide easily and allow water flow past them. If flat like this it should set it right the first time without too much hassle. Is yours like this?

Either way the temps should be usually close to rating of thermostat at the cover as said. Most engines call for ~195F thermostats.

Thermostats are relatively stupid things that is a wax pellet that expands against a set strength of spring to achieve the temp rating of it. When closing it may not seat back to dang near air tight shut and water pump continues to circulate coolant to maintain internal engine coolant a uniform temp - necessary action for any "water cooled" engine.

It's opening too soon. You can test one in a pan of water on stove and watch is open just a crack at the rating and wide open some degrees beyond the rating. They do partial or wide depending on demand.

Should be a relatively easy one to replace. Go for quality and test it in a pan which is tricky but when lifted out to cool off you see that it quickly shuts tight. Some will put a "V" notch in them to allow the smallest amount of coolant to pass by but it's really there to let air purge. If you use "Permatex" gasket maker on both sides of the gasket and some smear of silicone grease on manifold surface the gasket can be reused. First ones you scrape off in shards usually.

Recent or new now that thermostat if your info is correct is too low.

For now I suggest a new thermostat and carefully lower antifreeze concentration to read -25 or so but not to exceed -34F or 50/50.

OE spec was 192F is info was correct. 195F is more commonly available aftermarket which should be just fine as calibration of a couple degrees isn't always that close. Between those two changes you should have good heat again and a steady temp needle once fully warmed up,

Long retired now


Jan 23, 2010, 8:18 AM

Post #10 of 13 (4820 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In

Okay so sounds like thermostat replacement and reducing the antifreeze to water ratio.

The thermostat sits horizontally on the intake manifold. I found a very nice post on replacing a thermostat on Dodge 318/360 trucks complete with step by step photographs. Pretty straight forward, just have to get a few things out of the way to get to it. The only concern I have is being able to get to the manifold to clean the old gasket material off. O’Reilly is the closest parts store for me and they have several to choose from. I’ll stay away from the cheepies.

Looks like if I get my butt in gear and get going now, I should be able to knock this out before the outside temperatures drops and the rain/snow move in. Thank you again for all your help and explanations. I have a MUCH better understanding of the system works and what I need to be aware of. I’ll let you know how things turn out.

(edited out links that snuck in - nothing more)

(This post was edited by Tom Greenleaf on Jan 23, 2010, 9:53 AM)

Tom Greenleaf
Ultimate Carjunky / Moderator

Jan 23, 2010, 10:23 AM

Post #11 of 13 (4811 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In

Yes - it should be a cake walk thermostat. Take the hose right off the outlet and clean that outlet real good off car. Stuff a rag (don't lose it in engine please) in where thermostat sits so it gasket junk gets around it wont get into cooling system.

Now if the detent is in the outlet, make sure t-stat is exactly in the detent for it (go 195F) and stick gasket using the Permatex to hold it in place. Another trick for when a thermostat is indexed to exact spot in the outlet is to use a piece of "mechanics" or softer wire to hold it, bend over edge in such a way that a gentle tug will harmlessly remove the wire.

DON'T OVERTIGHTEN THE NUTS/BOLTS OF COVER TO MANIFOLD! If cover breaks new ones are available. May have to get some fancy chrome one if needed right away.

OK: All hooked up now. You didn't need or shouldn't have needed to empty the system to do this as it's up high. Use just water up to 1 qt first then add coolant set to about -10 for the rest if there is still lots of coolant in the engine. It's guesswork but check and recheck several times over the next week of use that you aren't not over much at least the -34 -- a tad less concentrated is fine as said earlier.

Specific to this engine (been around since the wheel) is just run heater, let and watch engine warm up after initial fill at radiator with cap on, feel for heat at the upper hose AND watch gauge. There plain will be some air to burp out. Shut down engine before it gets too hot. Heat handily rises so thermostat will stay open letting the air to radiator. Wait - feel for pressure at upper hose as an indicator for pressure to subside and you'll find coolant level dropped. Start engine with cap off (careful as if engine is hot coolant can shoot back out so goggles and stand a bit away if unsure of yourself and slowly add your waiting coolant to the now lowered level till full. When heater throws heat there's enough for it to self burp/purge the rest using the recovery tank over several cycles it will expand, send air to recovery tank and when cooled off again only return coolant - voila!

This engine should be done in a few cycles and stable. Check it every day and have ready to use coolant with you. A clue that it's overheating or with large air bubble left is heat won't work at all. Watch gauge like a hawk.

Again: test your anti-freeze tester and if not accurate using a measuring cup get a new one and check it too. Too many are way too far off. If you use a measuring cup meant for food (not a great idea if you can't clean that like crazy) than use a plastic cup and destroy it as antifreeze is poison! Plenty of 16 oz cups out there that are disposable.

Once more. If thermostat is to be stuck in the outlet there's always a chance it didn't seat well or stay in it's spot and it would do exactly like before if coolant slipped by it. Most would leak but not always.

Take you time to do it right once and don't get mad if it does slip out of place chalk it up to practice. If that happens make sure thermostat isn't bent or another is indicated.

You can do this. If you go to the Heat and A/C section there's a neat chart of how mixtures of known quantities will result in what freeze level protection stuck in the top few threads there.

Good luck,


PS: Let us know how it all worked out.............
Long retired now


Jan 25, 2010, 2:36 PM

Post #12 of 13 (4794 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In

Looks like the new thermostat has done the trick. It was unusually warm on Saturday so good for me working outside, but hard to get a good idea how well the heater is working. There was, however a noticeable improvement in the temperature inside the cab. We are back to falling temps. They are saying by Thursday a high of 16° . So it will be a good test of the new thermostat. I haven’t’ had a chance to take temperature measurements from a cold start, but I did note a temp of 179° on the heater inlet hose while I was topping off the coolant after getting it all put back together. I did take it out for a brief test run and topped off the overflow when I got back… about a quart or so. I’ll keep checking it when I get home from work for the rest of the week to make sure it’s topped off.
Thank you again for all your help and I hope that this will help out the other readers as well!


Tom Greenleaf
Ultimate Carjunky / Moderator

Jan 25, 2010, 3:54 PM

Post #13 of 13 (4790 views)
Re: heat not hot in 98 dodge ram [In reply to] Sign In

Sounds like you got it eric - way to go!

Temp should stay steady now warm day or not as it's regulated as intended. Stay warm,

Long retired now

Re: heat not hot in 98 dodge ram

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