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Thread: Help me diagnose a cooling problem.

  1. #1

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    Help me diagnose a cooling problem.

    My 1991 Ram50 has developed some cooling issues, or perhaps it has, I'll explain.

    I've been on a little bit of an effort to bring the truck up to date on some long overdue attention. My Brother-in-Law, who owned the truck the first 91K of it's life did oil changes, and that's about it. He did have a family friend change the timing belt, but I'll get back to that in a bit. I've owned it for about 4K miles now, and am starting to work my way through the truck.

    Over the past few weeks, I have done, or have had done, these things:


    • Replaced instrument cluster with one that has the volt, oil pressure, and tach. (the Sport gauges) (I did this)
    • Had the A/C checked and charged. Had been inoperative for over 4 years. Works now, only cost $150 for the service visit. I paid someone to do this.
    • I replaced the upper and lower radiator hoses, the thermostat, and the fan clutch. I also drained and flushed the coolant, and refilled with fresh 50/50 mix. The old coolant was pure rust color, and was way overdue to be changed.
    • I was going to replace the radiator, but when I removed it and flushed it with high pressure water, it flowed clear within 20 seconds or so, and when drained, it weighed almost exactly the same as the replacement radiator I had purchased. From this I surmised it was relatively free of sediment, and I re-used it, and returned the new radiator to the FLAPS for a refund.
    • I replaced the fan clutch with a new one. No indication the old one was failing, just trying to do some preventative maintenance.


    I still need to do the timing belt and water pump. The timing belt was installed one tooth off by the previous mechanic, so the timing is slightly off, even with the distributor cranked all the way over. I know that means my engine is working harder than it should have to, but it has been that way for a while, and never seemed to drive temps up before

    So, now it starts off fine, temperature rises as it should, both radiator hoses get hot, and it seems like all is good. Until I get it out on the road going 65 or so, and the needle starts to rise. So far I haven't let it hit the red, always stopping and letting it cool down, but I feel like it would hit the red if I kept going.

    So today I'm driving it, and the gauge starts to climb. I've got the A/C on, because it's freaking summer in GA, and I decide to try something. I turn off the A/C. Windows down. Temp gauge starts to fall. It was lamost to the red, and it falls back to about 3/4. Still not back to the middle, which used to be it's normal place.

    Is the A/C putting that much strain on my engine, or is it something else I've changed?

    It's a brand new fan clutch, but maybe it's bad?

    I know thermostats are notorious for being bad out of the box, could that be it?

    Tomorrow I'm going to drive it with no A/C for the whole trip, and see what the temp gauge does. I know I'll be sweating. Literally!!

  2. #2

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    Hey LF6!

    You might do well to conduct a thorough radiator/cooling system flush. It is a bother, doing it properly, but probably will give you good results.

    Another idea is to hose off the radiators from the engine compartment outward (back through the grill) to dislodge dust, insects, and Jimmy Hoffa particulate. All that stuff can get compacted in there pretty bad, and with the truck's minimal maintenance, probably a good idea.

    The radiator flush I recomment is where you drain the coolant, add Peak radiator flush and water, then run the engine for a while. Flush the Peak, fill with just water, run to operating temperature, then drain again (after engine cools). You're now ready for antifreeze.

    The timing issue is a contributing factor, but a lot of sediment and crud-inski is the likely cause for most of the over heating, in my view. Note my array: 1990 4G64.

  3. #3

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    I have an industrial technique for removing calcification/oxidisation/corrosion but it will do the trick. Go to your local supermarket and search for "citric acid powder" in the baking aisle. Buy 2 of the small shaker things full of this stuff, dissolve it in a bucket of warm water then dump it into the radiator and drive for a day (normal day to day driving should be enough). Make sure you run it with the heaters on full so it circulates through the heater core and then drain everything out of the cooling system - and flush it like your life depends on it. You may feel a little unwell when you see what comes out of the radiator. Be warned - if there are any breaches in the cooling system anywhere that have been plugged up with crud, the citric acid bath will eat through the garbage. This stuff will also dissolve rust so there might be a chance that any large flakes in the block that have been oxidising quietly in there will make a guest appearance. I've used citric acid bathing to remove rust and power flush a heater core and it works really well.

  4. #4

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    Hey guys, I'm more than willing to flush again, if that's what I need to do, but I did flush the radiator both ways while I had it out. It flowed clear. I also, although I forgot to list it above, flushed the block out using high pressure water flow. Flushed from above through the upper radiator hose, then from below using the lower radiator hose.

    The thing is, it was cooling perfectly fine until I made the changes listed above. Even with the rusty old coolant it worked fine. I have a feeling this is more than just needing a flush, know what I mean?
    Last edited by leftfield6; 08-07-2014 at 01:30 PM.

  5. #5

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    Have you checked to make sure it's really overheating? My wife's car acted similarly -- temp read in the middle of the gauge around town, but when it got up to freeway speeds, the needle would start creeping up and just keep going. I chased it around and around. Finally got a remote temp gun and found out it wasn't overheating at all. The temp gauge was bad. For some unknown reason it would go out of whack only on the freeway. If the problem started when you installed the new cluster, that's what I would suspect.

  6. #6

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    Quote Originally Posted by Lem Forder View Post
    Have you checked to make sure it's really overheating? My wife's car acted similarly -- temp read in the middle of the gauge around town, but when it got up to freeway speeds, the needle would start creeping up and just keep going. I chased it around and around. Finally got a remote temp gun and found out it wasn't overheating at all. The temp gauge was bad. For some unknown reason it would go out of whack only on the freeway. If the problem started when you installed the new cluster, that's what I would suspect.
    Yep, I was wondering the same thing. I'll run by the gadget store on the way home from work tomorrow and get an IR temp gun.

  7. #7

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    Guys here get caught out when doing engine swaps by forgetting the temp senders have different load ratings on them. When they get the thing up and running, the temp gauge looks like it's going into melt down mode. Might be the instrument cluster is reading the sender differently. Hunt down the temp sender from the same truck you pulled the instrument cluster from, and it might solve your gauge reading woes.

  8. #8

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    Okay, so I got a cool little infrared thermometer on the way home. Drove TO the store (about 5 miles) and the gauge was almost on the white line near the upper end, just before the red. Took me about 10 minutes in the store, so when I came out i started the truck up and checked out the temp gauge. It had cooled a little, but was still closer to the top than the middle.

    I opened the hood, engine still running, and aimed the laser at the thermostat housing. 230 degrees, and was rising slowly.

    I drove home, and the dash gauge got TO the white line, still not in the red. I pulled in the driveway, popped the hood, aimed my new toy, and got a reading 0f 248 degrees.

    Yikes, that's high, isn't it?

    To be clear, the truck has not once puked coolant. So, I guess technically it hasn't overheated, but it's got to be getting close.

    Unless someone has a better idea, tomorrow I'm pulling the thermostat and swapping it for a different brand.

    By the way, the drive TO the store was with A/C on, the drive back was with it off, so I'm eliminating the extra load of the A/C as a factor here.

    Geezer101, your idea makes perfect sense, but I can only find one part number for the temp sensor, with no mention of different sensors for regular gauge package vs. sport gauge package. The truck the cluster came from is long gone from the salvage yard.

  9. #9

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    ...the coolant temperature sensor sits low in the thermostat housing. The thermostat has an off-center positioning...sort of like a fried egg...and the housing has a beveled bottom. I figured that the thermostat needs to open on the lower end or it will hit the sensor prong, preventing the thermostat from fully opening. Not sure this is true, but if it is, this would cause the engine to run hotter than necessary. There is a little "air valve" at the 'top' of the thermostat (as it should be placed when installing) that indicates to me the proper positioning of the whole unit.
    http://www.mightyram50.net/vbulletin...ll=1#post26505

  10. #10

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    Your temperature is about right. Most electric thermo fan set ups don't trigger until 220-230 degrees F. Speaking of which, are you running an electric thermo fan or 'off the water pump'? Might be time to upgrade to the electric thermo if you're still running the water pump driven fan. Way more efficient, plenty of bonuses to using the electric fan set up.

  11. #11

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    I'm still running the stock fan and fan clutch. Is there a recommended set-up? Certain electric fan size? How are you guys wiring it to a temp sensor?

    Drove the truck some today, just babied it around a little. Never let the gauge climb too high.

    I'm 99.99% sure I installed the thermostat with the air bleed valve up, I knew that was the correct orientation.

  12. #12

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    Measure the height of the radiator core to figure out what is the biggest fan you can install. An 11" or 12" aftermarket thermo fan will be sufficient to cool the engine down but the bigger the area you can force air through the better. The temp sender can go in the bottom radiator tank or in the thermostat base in the manifold somewhere. Sometimes there's provisions for a temp sender already in place (some thermostat housing top covers for Mitsubishis have one in them). There are also adapters that allow a sender to be installed mid hose. Look up water temp sensor joint pipe adapter on ebay - all the gear you need to set it up can be bought new for cheaps.

  13. #13

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    It could be your water pump. You said that you haven't replaced it yet. Some of the fins could be messed up and when you put a extra load on the truck(a/c or highway) it can't move the coolant enough. Also the timing being off needs to be fixed cause that can cause a issue also.

  14. #14

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    Here's a link to a previous thread on this topic: http://www.mightyram50.net/vbulletin...light=electric

    I think it answers most of your questions...

  15. #15

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    I wanted to come back in and update this thread with a resolution. Since I've been having the overheating issues, I just stopped driving the truck except on really short runs to the mulch place or Home Despot and the like. Finally got around to working on it over the weekend. here is what I knocked out in one weekend of wrenching:


    • Took off the old radiator and took it into a local radiator repair shop (Sims Radiator in Lawrencevillle GA) This was on Friday at about 2PM. they said it would be ready on Monday around noon. Okay, that's acceptable turnaround time. Turns out, I got a call Saturday morning at 10AM saying it was ready! Deluxe. $65 and it's been chemically cleaned out and refinished. Tech said it was loaded up with rust particles. He estimated 50% blocked.
    • Replaced the timing belt, and more importantly corrected the "one tooth off" mistake made by the last guy to do the belt. I had never been able to correctly time the truck due to that one tooth. Also replaced the smaller silent shaft belt, the small belt tensioner, the main timing belt tensioner, and the crank oil seal.
    • Replaced the water pump
    • New drive belts
    • filled and burped with fresh coolant 50/50 mix
    • Used timing light to set timing.


    Well, it's like a different truck! Temp gauge rises exactly to the middle, and stays there!! Idling, full throttle, AC on, AC off, puttering around town or 70MPH on the highway the temp gauge is rock solid, straying only slightly from midpoint.

    Also, getting the timing back in spec shows up in much better power, and I'll bet the next emissions test will show much cleaner burning. Should see my MPGs go up too I would expect.

    I suspect the radiator was my big culprit in the overheating. I had removed it from the truck before, and gave it the driveway flush with a garden hose, but that obviously did not do the trick. In retrospect, I wonder if it dislodged some of the particles, and then when they resettled, they actually made it worse!

    I'm loving my truck again!!

  16. #16

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    We always love to read these success stories, Leftfield.

    Take it easy on that accellerator and you'll get 30 MPG.

    Congrats!!
    The greatest gift you have to give to the world is that of your own self~transformation.

  17. #17

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    30 mpg? Pffft, where's the fun in that...

  18. #18

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    Quote Originally Posted by leftfield6 View Post
    I wanted to come back in and update this thread with a resolution. Since I've been having the overheating issues, I just stopped driving the truck except on really short runs to the mulch place or Home Despot and the like. Finally got around to working on it over the weekend. here is what I knocked out in one weekend of wrenching:


    • Took off the old radiator and took it into a local radiator repair shop (Sims Radiator in Lawrencevillle GA) This was on Friday at about 2PM. they said it would be ready on Monday around noon. Okay, that's acceptable turnaround time. Turns out, I got a call Saturday morning at 10AM saying it was ready! Deluxe. $65 and it's been chemically cleaned out and refinished. Tech said it was loaded up with rust particles. He estimated 50% blocked.
    • Replaced the timing belt, and more importantly corrected the "one tooth off" mistake made by the last guy to do the belt. I had never been able to correctly time the truck due to that one tooth. Also replaced the smaller silent shaft belt, the small belt tensioner, the main timing belt tensioner, and the crank oil seal.
    • Replaced the water pump
    • New drive belts
    • filled and burped with fresh coolant 50/50 mix
    • Used timing light to set timing.


    Well, it's like a different truck! Temp gauge rises exactly to the middle, and stays there!! Idling, full throttle, AC on, AC off, puttering around town or 70MPH on the highway the temp gauge is rock solid, straying only slightly from midpoint.

    Also, getting the timing back in spec shows up in much better power, and I'll bet the next emissions test will show much cleaner burning. Should see my MPGs go up too I would expect.

    I suspect the radiator was my big culprit in the overheating. I had removed it from the truck before, and gave it the driveway flush with a garden hose, but that obviously did not do the trick. In retrospect, I wonder if it dislodged some of the particles, and then when they resettled, they actually made it worse!

    I'm loving my truck again!!
    Other readers of this thread take note-

    Most DIYers will will throw parts at their truck hoping they will hit the bullseye with a cure. I haven't been here in a while and was going to suggest taking the radiator to a radiator shop. The worse case scenario is that they have to remove the tanks and "rod out the core". This is done for radiators that have had massive neglect. Sometimes the core tubes will disintegrate when you do this if the radiator if it is in a REALLY bad state of neglect.

    Because the system is neglected, rust and chemical crud build up in the tubes and block them. When you remove the cap to see if the coolant is flowing you are fooled into thinking it is. It is flowing, BUT ONLY AT THE TOP. The bottom of the radiator has blockage, in most cases severe blockage.

    He that hath ears, let him hear.

    The garden hose operation at home just not do the job as well as a cleaning of the tubes by a radiator shop.

    Glad for you that you got the truck fixed.

    On a truck that's had minimal maintenance like yours, it's the first thing that should be done. Most guys will buy a bunch of parts first and the problem will go unfixed until they elicit a radiator shop.

  19. #19

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    I have performed my own chemical core flush by mixing up a concentrated batch of citric acid powder in warm water and circulating it through the radiator (I pumped it through my heater core by using a pressure cleaner with a faulty pressure regulator I've repurposed). The stuff will dissolve calcified build up in the cores, rust and any dirt or broken down coolant to the point where it will pass through the internals - and will even remove oxidisation off the cores. The side effect to this is, if the core is compromised in any way, the citric acid solution will expose it fairly quickly.

  20. #20



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    or use dawn dishwashing detergent - just add into the radiator and run for 20 to 30 minutes then flush clean and refill. Won't help with severe rust buildup, but will clean out most else.
    Pennyman1
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  21. #21

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    Chiming in here guys...my temp was creeping up past halfway and thought I'd drain the radiator and add some coolant to get me through to the weekend. Topped off the radiator and off to work I went. On the way to work, the temp needle flirted with the white line on the Hot side. This continued for 2 weeks even AFTER refilling the radiator. The coolant would overflow in to the reservoir and the radiator would be almost empty. I thought the vanes on the water pump had worn out so I put on a new pump for $30 which did nothing to remedy the problem. Autozone told me to run the engine for up to an hour with the heater full blast because I had air in the system. After doing that 3 times and refilling the radiator with coolant due to it overflowing, I dropped $40 for a purge kit from NAPA. That STILL didn't do squat to lower the temp. After I shut the engine off I would hear popping coming from the lower radiator hose for about 15 minutes until the engine cooled down. The last thing I did was to change out the $8.00 thermostat. I went with lower temp option (160, I think, down from the OEM 190). I installed the thermostat, topped off the radiator and THE TEMP RAN AT AND STAYS AT THE LOWEST I'VE EVER SEEN IT. When the old girl is running she stays about 2/5 of the way between cold and hot. This was during the summer but I don't have A/C but did do a lot of driving on side streets and the freeway. Sorry for being long winded but I like to include as many details as I can and hope this helps!

  22. #22

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    The thermostat is a good starting point to check if you have a temperature fluctuation issue but it doesn't over heat. It 'should' be the first thing to check before doing a radiator swap or something more extensive (or expensive) like that. Now there are high flow thermostats on the market but I'm not 100% sure if they are really worth the extra coin...

  23. #23

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    Yep, thermostat was the first thing I tried. Swapped with a new one, but no change. I tested the old one using the water in a pan test, it opened and closed just like it should, so I knew the tstat was not the issue. Nothing helped until I had the professionals have a go at the radiator

    By the way, before having the radiator chemically cleaned out, I had looked into buying a new radiator, but I could not find one. My FLAPS listed two sizes for my 91 2WD with the 2.4L, but one had a 15 inch core, and the other had a 21 inch core. Problem is my radiator has a 19.5 inch core. They even shipped in the one with the 21 inch core to see if the mounting holes lined up, and they did not.

    Never did find anyone listing a 19.5 inch radiator, thus I had my old one cleaned out.

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