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  #1  
Old July 25th, 2013, 11:06 PM
javelinadave
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Running Hot

When I drive 40ish mph the temp gauge points straight up (mid way).
When I drive 55ish mph the temp gauge points 3/4 of the way towards the red.
The oil temp shows hotter than 1/2 way.

I laser temped the radiator and the bottom was 64c and the top was 75c.

How accurate is the temp gauge?
Radiator issue?
Where should I start?
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  #2  
Old July 25th, 2013, 11:08 PM
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Radiator. Flush, recore or replace.
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  #3  
Old July 26th, 2013, 12:33 AM
javelinadave
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That's kind of what I was thinking. Anybody have any luck with any DIY flush kits or are they a waste of time? Sounds like the best place to start.
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  #4  
Old July 26th, 2013, 08:05 AM
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Have the radiator cleaned and "rodded", hows that fan clutch.
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  #5  
Old July 26th, 2013, 09:14 AM
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Steve Maietta
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75c at the top of the radiator sounds 100% fine. Isn't it a 74c thermostat? I'd say your temp sender or wiring is messed up.

When you shoot a temp, make sure you get that sucker close to the surface (2-3 inches) you want to read, it will be more pinpoint accurate.
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  #6  
Old July 26th, 2013, 09:46 AM
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Don't just go replacing stuff willy-nilly. You obviously have some cooling going on in the radiator so it may or may not be up to your cooling but the radiator temperatures don't send a red signal yet---those temps (64=147F, 75=167F) are not even close to danger zones. Quite a number of folks have replaced their temp gauge/sender with a VDO (vision series drops right in, there are great write ups on this site) and that will give you some accurate engine temps. When you are in the hot, check the temp at the thermostat housing--that should give you at least a more accurate reading--I would say anything under 200F (93C) is not cause for concern as your thermostat opens around 180F. I am not sure from your signature what engine is in your truck, so that may vary.

But right now, you may or may not even be overheating--you need to double check that before swapping parts that could just be a money drain without solving your problem.

There are several things that can cause overheating. One is definitely a clogged radiator. Other things that can cause it are a stuck thermostat, a bad viscous coupling on your fan blade, a bad radiator cap, incorrect timing, or engine problems. For engine problems, it could be a vacuum leak either from one of the hoses such as the brake boost, or from one of the engine components such as the unions of the top end components of the air intake. It could also be caused by a blown head gasket, a porous block, or a slipped liner.

So don't just guess and if you have to resort to guessing, guess with less expensive components first.

I have had overheating before (I have had a blown gasket on my DII, a slipped liner, a porous block, a clogged radiator, a bad aftermarket reservoir cap...yeah, I have been unlucky but also used untested used components in the past when I built my truck) so I have been around the block. If I was in your shoes, here is what I would do:

1) Install a VDO temp gauge. Getting accurate engine temps is huge--you should do this regardless.
2) Take temp readings of the top hose (and feel it---is it soft or "pressurized"/hot?) and at the thermostat housing and, just like you did, at the radiator. You have a 20F change from top to bottom of your radiator, so you know it is cooling--your readings are pretty low, however--I would expect the top to be in the 180-200 or above if you were really overheating (at least on a 3.5/3.9/4.0/4.2/4.6 V8---I'm not sure what engine you have). The fact that you have a 20 degree differential means it is working--just not sure if it is working enough. Typically a 40F drop is more in line, so it could be your radiator. It is just the temps that you got are really low--not even close to overheating, so they are suspect.
3) Check your timing and pull some plugs to look if you are running lean. There are some great sites on how to read plugs by looking at their tips. Google how to read plugs--you will find great information and it is a fantastic "tool" knowing how to read plugs.
4) Check your viscous coupler on your fan. There are many threads here on exactly how to do that.
5) Get a block tester--it is a fantastic tool. Mine, from Napa, cost about $50 and it consists of a glass tube with a rubber bottom that you fill with blue fluid and you put it on the reservoir and suck engine air through the fluid for about 1 minute--if the fluid turns green, you have an exhaust leak into the cooling system. This will at least give you good information on a head gasket/porous block/slipped liner issue---it is not 100%, but if it does turn yellow, then you know it is one of those.
6) (particularly if your plugs look like you are running lean) get a can of choke cleaner and spray around the top end of the engine and vacuum lines---listen if your idle changes. If it does, you have a vacuum leak which could make you run hotter.
After all these things, then I might start replacing a couple components. I would start with the reservoir cap, it is cheap. Then I would remove the thermostat and put it in some water bringing it to a boil. It should open about 180F typically (for the engines I mentioned--it might/should be stamped on the cap) and see if it is fully open (you can also measure the water temp to see what temp it opens). THis would at least rule it out. When reinstalling, make sure that it has the vent hole at the top. When doing this, first drain some radiator fluid into a clean bucket so that you don't have a spill when you take it off. When you refill, make sure you bleed any air out of the coolant line--this will rule out an air pocket too.

Only after all this do I pull my radiator. And it might be your radiator--they do go bad and it could easily be that. But a recore is about $500-700 depending and it takes more time and is a PITA (at least if you have oil cooler lines in your model). Getting it cleaned and pressure tested is good to do every 5-7 years anyways...

Good luck--hope it is a simple thing!
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  #7  
Old July 26th, 2013, 10:03 AM
javelinadave
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Thanks Chris, that's why I love this board. I have a 2.5 liter NA diesel. Guess I'll order a new gauge today and take some new temps.
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  #8  
Old July 26th, 2013, 12:39 PM
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The radiator should drop the temperature about 40 degrees Fahrenheit, so that would likely be your issue, but the fan clutch could also be the issue. Check the temp on the actual radiator, and not on the hoses. Does it run warm if you have the heat on?
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  #9  
Old July 26th, 2013, 06:27 PM
javelinadave
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Here is an update of whats going on.
Thermostat housing is 83c
Top of radiator is 75c
Bottom I cant accurately measure due to the hose being pulled flush with the radiator itself.
The top hose is firm when things are running.

The oil filter and housing is 175c
The oil cooler is 153c

I'm going to install a VDO gauge and sensor when they arrive and swap out the thermostat for a 74 degree unit.
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  #10  
Old July 27th, 2013, 06:50 AM
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better make sure its frenchy units
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  #11  
Old July 27th, 2013, 11:07 AM
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Oui, it is.
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  #12  
Old July 27th, 2013, 07:04 PM
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Dave-

Something to quickly check before you start ordering stuff. I just drove my "new to me" '87 D110 300Tdi from New York to N.Carolina, then straight west on I-40 back home to Alpine, Az. a month ago. I had "overheat" problems, or what I had to honor as an overheat condition just north of Charlotte. A little longer story and fix than I have time right now to write here. I agree with Chris Davis above in many areas. What I would suggest first is to check the resistance of the engine temp sensor when it's stone cold, and then note the resistance as the engine heats up- 5- 10 minutes after running, etc. My old one started out at about 455 ohms when cold, and within 10 minutes of running, was at 220ohms- which put the needle into the danger zone on the gage. False reading, as the engine was still cold as well, and the thermostat doesn't open up until 80c or so anyway....Mine temp sender turned out to be bad- a $10 fix from RN for the single pole variety, after I got home. I was away from home, and ended up buying tools that I have duplicates of here, etc. I was pretty sure I had an indicator problem- I installed a $17 mechanical coolant sensor gage bought at PepBoys, and tapped into the filler plug on top of the engine block, using the several different adaptor fittings included with the kit. Pipe fittings are universal- used by everybody- SAE or Metric. I tie-wrapped the gage to my snorkel, taped up the back of the gage as I knew I'd be running through rain, and off west I headed. At 70mph, the engine ran at 192F most of the time, and reached 200F across New Mexico in the heat, as the gage read into the explosion range.... BTW for everybody, a $40-50 Digital Pyrometer from Harbor freight is a great diagnostic tool to have. Dave, if you want to call me, I can tell you in greater detail all the stuff I did. 928-339-1181 home.

Tim
Alpine, Az.

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  #13  
Old July 27th, 2013, 09:48 PM
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Chris Davis
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That's a great suggestion-- to test your temp sender!
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  #14  
Old August 3rd, 2013, 01:34 PM
javelinadave
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What is the normal resistance at the sensor?
Mine is 490 ohms cold and I still need to test it hot.
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  #15  
Old August 3rd, 2013, 05:54 PM
skrufy
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Hi Dave-

You have a former MOD 90, so what engine do you have and how many poles on the temp sender? My '87 110 has the 300 Tdi in it with the single pole or electrical contact point for the positive out put, and it grounds thru the block. If you have the later type twin connector, one goes to ground someplace, the other to the gage. I don't know if there are any published resistance figures published anywhere, but I
assume there would be a need to have those figures. I have the factory manuals for both the Discoveries (Series 1) and the 90/110s up through '93 or so. I will do some research to see if any are published and get back to you.

I still have my mechanical pickup temp gage installed, so I will also do a check of the gage vs the resistance of the temp. sender and report those numbers. I'll also cross check the mechanical pickup temperature with my digital pyrometer... that will be interesting to see, as the DP has a laser so you can be sure of the exact point of the temp reading....

Tim
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  #16  
Old August 3rd, 2013, 06:17 PM
javelinadave
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I have a 2.5l NA diesel.
The sensor has one pole.

I'll call Trevor or George on Monday and see if either has a sending unit. The VDO kit is on back order from JEGS.
Thanks,
Dave
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  #17  
Old August 3rd, 2013, 06:22 PM
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One is normal. One temp sensor I had fail gave me no reading.
Turning on the ignition and grounding the wire on the block gave me a reading on the gauge.
Wonder if yours is just a little wonky.
Dirt cheap those temp sensors. Or at least they were.
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  #18  
Old August 3rd, 2013, 10:31 PM
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Quote:
Originally Posted by javelinadave View Post
I have a 2.5l NA diesel.
The sensor has one pole.

I'll call Trevor or George on Monday and see if either has a sending unit. The VDO kit is on back order from JEGS.
Thanks,
Dave
Try www.Egauges.com
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  #19  
Old August 3rd, 2013, 11:44 PM
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Chris Solis
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I highly suggest getting the mechanical VDO gauge as there are no electrics involved. I had issues getting temp senders to work, hours spent testing resistance etc and went with the mechanical gauge, same price as non-mech, viola... No more issues reads true.
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  #20  
Old August 4th, 2013, 12:01 AM
javelinadave
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Good advise. I just ordered a new sending unit from Trevor for $8. If that doesn't fix things I'll go with that.
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