Dodge truck overheating help

[rtimgray]

I've got a 1997 Dodge 1500 truck with the 5.9l v-8. I bought it about a year ago. Shortly after I bought it, I noticed that it seemed to be running hot. Correct temperature is 190 degrees. The gauge shows 200 degrees to be normal, with 250-260 overheating (well, that's as far as the gauge goes. I assume anything over 200 is overheating). Anyway, I changed the thermostat, did a flush and fill for the radiator, all that kind of stuff - nothing different. The gauge indicated hot (anywhere between 220 and 250 after I drove it a while), but it wouldn't actually boil over (do new vehicle's boil over anymore?).

I had it checked at a Dodge dealership, and they said they couldn't find anything wrong. They said even when the gauge was reading 220 to 250, the temperature on the manifold at the thermostat and on the thermostat outlet hose was 190 degrees (they measured with a laser gun). They said it was either a bad sending unit or bad gauge cluster - either way, nothing was actually wrong with the cooling system.

So I drove it all winter and now back to this summer (I didn't drive it alot last summer because I mostly drove my Samurai. However, my Samurai transfer case went out last fall and I have been trying to find a cheap one locally - no luck. I have finally ordered one online that should be here next week). Anyway, no problems all winter. Now this spring, there have been a couple of days when I get home from my commute of 11 miles from work, and the gauge is pegged and after the truck is shut off, in just a minute the coolant starts pouring out of the overflow tank. I thought this just might be because I had put too much coolant in it (more than halfway up the overflow tank). Yesterday, I got home, gauge was pegged, got out, popped the hood and looked. Water slowly was returning to the overflow tank and everything seemed normal. I walked in the house, changed clothes, came back out in about 2 minutes, and there was steam pouring from the grill of the truck. Popped the hood and apparently the radiator blew a hole in the drivers side.

Sooooooo...what is the problem? Does anybody have any ideas? Like I say, the gauge shows overheating, but I forgot to mention that I've been carrying around one of those laser heat guns and have checked the truck often...no matter what the gauge says, the manifold at the thermostat and the return hose always read 190. The hose going from the radiator into the engine I think reads around 140. Is there any other way to tell if the truck is actually overheating? Was the radiator a problem, a sympton, or just a coincidence that it went out? I appreciate any help anybody can give me. Thanks in advance.

 

[LarryRB]

I lost a radiator at 40K miles on a Dakota. For me, it was plowing snow and evidently getting a lot of road salt in the lower radiator area. It prematurely blew out.. Anyway, I had your problem on an older Dodge., They have a paper thin circuit board behind all the gauges. Pull your gauge cluster and you can see this thin circuit board. You have to remove all the small night lights (they pop in and out) then remove that circuit board. It can be cracked, shorted or? You should be able to tell by looking at it very closely.

 

[RobertN]

Check your hoses. If they are soft, they can collapse and cause poor coolant flow. If it is aleardy warm, and then you take away the cooling by shutting off the engine, the the water inside the engine will heat even more for some time, hence the blow out you see.

Check the fan and clutch. If the clutch is going, it may not cool properly. Also, if the clutch is going, the fan may not spin properly, and can cause wear on the waterpump bearings.

When you replaced the coolant, and topped the system off, you used a 50/50 mix? Too much water in the mix, and it might boil over when the engine shuts off and the water in the engine really heats up.

What about the belt, condition and adjustment?

 

[bgott]

First off, check your gauge. There is a gauge tester available that is basically a box with rheostats that you hook to the wire at the sender and a ground. You have to dig deep in the service manual to find out how many ohms you need to imput for low, medium and high readings on your gauge. Once you know that the gauge is reading right you need to install a new sender. You might not have the right thermistor for your application or the one you have can be bad. If you end up with the wrong one it will give you fits, I had a Chevy 454 powered motorhome give me fits one time because the sender for a pickup is NOT the same as the one in the MH. The pickup sender will read way too hot, the one for the MH is calibrated to read way cooler. I would also check the gauge panel and body grounds, bad grounds are the cause of most electrical problems. You also need to check and see if that model has an instrument panel voltage regulator, those wil also mess with your head. A wiring diagram will let you know exactly what you are dealing with as far as the type of system and what kind of goodies it has in it. Did the dealership check the temperature with a computer scan tool? I used to check that kind of stuff through the scan data, if the computer is seeing 190 degrees and the gauge reads 250 you know which way to look. On that model the computer should be the input for the gauge, I think. I'm a hair rusty. /forums/images/graemlins/tongue.gif In that case the sender is called a coolant temperature sensor and outputs to the computer. Once you are sure that the indicating system is right your problem should go away, unless the truck has leaking head gaskets or a cracked head. Other worse case coolant circulation problems include blockages from someone replacing freeze plugs and beating the old ones into the block or head instead of removing them and water pump impellers spinning on the shaft or having the fins rusted off. Since you keep getting a reading of 190 at the manifold every time you check it I'm going to presume you didn't install the thermostat backwards. You might, however, have gotten a bad thermostat right out of the box. Before I got out of bustin' wrenches for a living I was noticing more and more bad "new" parts. /forums/images/graemlins/mad.gif It really sucks when you install a new part and end up with the same problem, or worse, a different one. It was probably time for the radiator to blow, skip the dealer for that and go to Vatozone, they are a lot cheaper and the aftermarket radiators seem to at least equal OEM quality.

 

[Soundguy]

My 98 runs right at 200 on the gauge.. never gets hotter.. even when towing.. same 5.9l engine.

After some hard work, and aprking, I'll sometimes here a gurgle of water t/from the overflow.. but never any steam, or 'boiled-over' coolant.

I agree with the others.. something is wrong with the cooling system...

I was gonna say do a flow test on the radiator.. but looks like it is going to be repalced anyway now.. etc.

Soundguy

 

[rtimgray]

Here's an update on my story thus far (kind of Prince Valiant style, huh?):

Pulled the radiator yesterday. Took off the top and bottom hoses - noticed that the bottom hose had a spring in it. Actually, it was two springs - look like they are supposed to be there and wouldn't cause blockage. I'm planning on replacing both hoses anyway - they do feel a little soft. I replaced the sending unit for the gauge and conducted the test as outlined in the service hayne's manual. It just says, disconnect the wire and turn the ignition on. If the gauge rises to it's low setting, then the gauge is functional. Well, the needle moved a little, but not all the way to the low setting? So is the gauge or the sending unit bad-dunno. It has a new sending unit now, anyway. On this model, there are at least two water temp sending units. One (which I replaced) goes to the gauge. The other sends information to the computer so I guess they are parallel systems and don't necessarily get info from each other(?).

I'm also putting in a new thermostat - I'm getting that from the dealer. I had a real bad time with my 83 Nissan truck thermostat one time. Went through 2 from Autozone, 1 from NAPA and 1 from carquest and none of them worked (they always stayed open and truck wouldn't warm up. Went ahead and spent an extra $5 and bought one from the Nissan dealership and the problem went away (weird). I think that I have always installed them correctly (spring side on the inside, right?). I've got a new radiator coming from radiatorbarn.com - it's about $145.00 vs. $222.00 at Autozone.

Good tip about the too much water and boiling thing (I shoulda thought of that). I've had a little water leak (I think I found it at the thermostat - looks like it's been leaking there) and since it's warm, I've always just topped off with water. Maybe that's why it boiled over a few times. I'm still just curious if the truck is really overheating or not. I can't imagine that if it was really overheating (often the gauge shows to 240 or 250 and it doesn't boil over) and I've been driving it for most of the year that there are no ill effects. I'm sure you guys know that a hot engine usually seems to have a "smell" to it (at least to me it does), and this one, except when the coolant actually has boiled out of the overflow jug, hasn't smelled that way. Is there anyway that the coolant overheats put still reads 190 at the thermostat (that's not even boiling for water - but it is under pressure, sooo.....).

And by the way - I liked the idea about driving around the dealership til it starts to boil over and then grab the service manager - I wish I'd thought of that!

Plan from here - put on new sender, t-stat, hoses, radiator and fill with 50/50 coolant/water mix and see what happens. Thanks for the help and advice fellas. Take care.

 

[Egon]

The springs in the bottom hose are there to prevent the hose from collapsing.

Electronics may work well when cold but as they heat up problems can occur.

Egon

 

[rtimgray]

I figuered that's what the springs were for - it's just I've changed several hoses and never had seen that before. They pretty much had to be there on purpose though.

Good point about the hot/cold electronic thing. Thanks.

 

[Bird]

Those "springs" in radiator hoses used to be very common, but I don't think you see quite as many now as you used to. And of course, as has been said, they're just to keep the hose from collapsing.

 

[ByronBob]

Try running it first without a T-Stat. That will tell you a thing or 2 before going further on.

 

[bgott]

Yep, $145 beats $222! I pay around $130 but I get mine wholesale through a body shop. Don't get carried away with the antifreeze. Antifreeze will help with boil over but doesn't transfer heat as well as water. 50/50 max. Another thing that I didn't think of last night. If your radiator cap is getting weak it'll let the coolant boil over. The reason for a pressure cap is to raise the boiling point of the coolant. It also will not let the syphon action take place that sucks the coolant back into the radiator when the engine cools. The water expands when it gets hot, passes to the coolant recovery bottle and then won't return when the engine cools down. A few cycles like that you start pushing coolant out of the bottle onto the ground. Don't make the mistake of filling the recovery bottle to the top. If the radiator is full you'll just waste coolant because of the above and if you have a leak the system will just pull in outside air rather than suck from the bottle. Check your coolant at the radiator when the system is cold, preferably after it has sat all night, then fill the bottle to the low mark or a little above. If the radiator is low after it cold and it has been filled and burped right it usually means you have a leak. Warning to those of you that aren't experienced in servicing cooling systems. Do not remove the cap when the system is anything but dead cold!!! Pressurized coolant, when hot, will turn to steam when the pressure is released and blow out all over you and scald your hiney. You'll only do this once, twice if you're ate up with the dummies! That new radiator probably will come with a new cap, at least the ones I get do. Test it anyway. Good Luck! /forums/images/graemlins/smile.gif

 

[rtimgray]

If I run it without the thermostat, do you have any idea what temperature I should expect? The only reason I haven't done that before - well, for one thing it was winter and I needed some heat, but mostly because it's about an hour or two to take out the t-stat - it's just hard to get to - take off the belt, take off the alternator, disconnect a couple of cables and lines, etc. and then the t-stat housing is down in between some stuff. I might give it a shot seeing as how it is warm weather season. Thanks.

 

[bgott]

Running without a thermostat on a full time basis is not a good idea. The engine doesn't get up to temperature so the moisture and volatile stuff that ends up in the oil doesn't evaporate and get sucked out of the crankcase by the PCV system. Then you have to figure in that the computer sees that the engine is running cold and adds extra fuel. More stuff to go past the rings and form acids and sludge. Then, once you load it and it gets hot, you don't have anything slowing down the coolant circulating through the radiator so that it has time to transfer it's heat to the air. If you are going to run without a thermostat at least change the oil more often. The easiest way to change the thermostat on that Dodge is to pull the A/C compressor. You don't have to disconnect the lines, just pull the bolts and move it out of your way. You won't believe how easy a job it actually is. Change out your bypass hose while you're there and look for coolant lines along the front cover gasket. If it still has the constant tension hose clamps use them and don't junk them for the screw type. The constant tension type are a pain but they stay tensioned when the hose shrinks to fit and you don't have to go back and tighten them. Once you reinstall the compressor you stand a very good chance of not being able to get a socket or screwdriver on the screw type hose clamps and then you have to pull the compressor again when the hose starts leaking the day after you install it. /forums/images/graemlins/mad.gif The last one I did, 6 months ago, was a water pump job that turned into a thermostat, front cover, water pump, hoses and radiator job. Every time I changed a component I would pressure test it and blow something else out. 165,000 miles with no maintainance. I crossed my fingers and didn't have to do the freeze plugs in the back of the block. /forums/images/graemlins/tongue.gif

 

[Soundguy]

Speaking of leaks...When my dodge 1500 water pump started leaking, I pulle dit and when I got the replacement.. I had a hard time sealing the metal pipe to block connection.. it uses an oring.. but the service guy said to rub some black rtv on it.. just a thin film.. that made my leak stop.. guess the casting int he block is a tad too porous for the oring to seal? ?

Any other dodge owners see this problem on a water pump replacement?

Soundguy

 

[rtimgray]

Well - here's where I'm at now. I replaced the sending unit, thermostat, upper and lower hoses and radiator. Started it up last night, added 50-50 coolant mix and let it run for a while. Temp gauge got up to about 240. Checked it with a heat gun and the t-stat area was only about 140. Took it for a drive - no change - got back and let it cool and then topped of the coolant (needed about another 1/2 gallon). Drove it around this morning and the gauge reads about 240 but the hoses and such aren't even up to operating temp (haven't taken for a 10 minute road drive yet, though).

So I'm thinking that I've got a bad gauge. I'me thinking of adding an aftermarket temp gauge (sunpro or something). Since this truck has two sensors (one for the gauge and one for the computer), if I just replace the one for the gauge on the dash, do you think it will have any effect how the truck runs? It doesn't seem like the truck is really overheating, I would just like to have a functional gauge in case it ever does.

Thanks for all the help and advice.

 

[Moon]

Sounds like your onto it. Is that a laser heat gun your using? Where do you find them and how much do they run. Sounds like something I need in my tool box.

Thanks,
Moon of Ohio

 

[bgott]

Have someone hook a scan tool to it and see what temperature the computer is seeing. Have you tried aiming the heat gun at the base of the sender? That will give you a better idea of what temperature the thing is running. If the thermostat is stuck closed or in backwards it'll heat up to 240 and the outside of the housing and the hoses will still be cold. Take the last thermostat you pulled out of it and get a pan of water and your wife's candy thermometer and hang the T-stat in a pan of water on the stove. Watch the temp as you heat the water and see when the T- stat opens. The temperature that the T-stat is rated to open is usually stamped on the end of the bulb. That's the copper pellet looking thingy that is supposed to go in the engine. /forums/images/graemlins/smile.gif If this T-stat opens like it's supposed to, stick it back in. Test the new one while you have it apart. Push the T-stat that you finally use open with your finger and prop it open with an aspirin. That'll let you burp the cooling system without heating it up and hoping the T-stat opens and the aspirin will dissolve and let the T- stat work normally. There is a chance you're getting a run of bad T-stats. This happens more often than you think. I've run into, off the top of my head, two or three bad T-stats in a row, five rebuilt starters, four out of spec coolant temperature sensors, countless rebuilt water pumps, A/C compressors, etc. After the second one you start thinking it's you! /forums/images/graemlins/tongue.gif Of course, there is the countless times that I have blown the diagnosis in the first place. /forums/images/graemlins/crazy.gif You have my sympathy, I've gotten into these kind of PITA's before and they can really drive you nuts, especially if your paycheck is hinged on it going out the door. /forums/images/graemlins/mad.gif

Yes, you can install an aftermarket gauge in place of the factory gauge as long as you don't inadvertently pull the collant temperature sensor rather than the gauge sender. You'll know if you do that because the check engine light will come on and it will be stuck on base timing. That's how you set the base timing on a Chrysler with a computer.

 

[rtimgray]

I'll have to see if I can find somebody with a scanning tool and the knowledge to use it - that would be curious to find out what the computer is saying the temp is.

Also as an update - now that I have driven the truck for a few days, it appears as though the problem has stabilized - so to speak. Prior to my working on it, the gauge would read anywhere between normal operating temp and pegging the gauge - no consistency. Now, the truck warms up to about 240, goes slightly over, then drops down (I'm guessing this is the thermostat opening) to slightly below 240 (I'm interpolating the numbers - the gauge only has 130, 200, and 260 marks). It then stays dead at this position, whereas before it wandered. When I have checked it with the heat gun, the hose reads 190; all of the times that I've checked it, I get it aimed down to the sensor and the manifold where everything (the two sensors and the t-stat) is mounted, and it all reads around 190 - and the thermostat is technically supposed to be 192 degrees, so that's pretty close.

Bgott-do you think the actual water temp could be 240 in the manifold and only reading 190 just on the other side of the t-stat? I mean, the t-stat should open at 190, but then if the water is 240, wouldn't that show up on the other side of the t-stat as well (I'm asking cause I honestly don't know if it's possible or not).

I know I got the thermostat with the spring side toward the engine side - that's the same way it was in before. Is that the correct way or not?

The laser heat gun I got from Grainger. It is a Raytek ST60 Pro Plus and it ran about $350 (luckily, my employer bought it - I actually use it at work and just borrowed it for this). I have seen some cheapies in Harbor Freight for about $70 - might be the trick for the toolbox.

Thanks for all the help and advice.

 

[bgott]

Yep, the spring side is the engine side. If you look in the middle of the spring you'll see the copper pellet. The water in the hose on the radiator side of the thermostat can be a lot colder than the water directly behind the thermostat because the thermostat acts like a barrier. If it isn't opening the heat will be disappated quicker by the cooler water in the radiator. It's kind of hard to pin down exactly what temperature you're going to see in the hose because you never can be sure what state the t- stat is in, closed or in a partially open state. It starts opening at 190 and slowly opens all the way at a higher temperature, probably over 200.