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Discussion Starter #1
My turbo 1000 is running a bit hotter than it used to even in the same ambient tempuratures. It all started one day when it was raining and I figured the loose fan belt tensioner was the prob. Fixed that and it's better but not what it used to be. Idle or low load temps are fine but any real street driving and it goes up to about 100ish on the guage. Before it stayed right at 80 maybe climb a little on a steep grade. I did a full flush. Changed the thermostat and spent over an hour straightening fins on the rad. It also seems to have to cycle a bit before it gets hot. It's fine for the first few minutes of running at temp. I have a couple theories but they may not make sense. First one is radiator cap releasing pressure too early and not allowing air back in creating a slight vacuum that might make the lower hose collapse. Second one is fuel quality. This condition started within minutes of getting fuel and I'm still on that tank. Is that even possible? My third theory is obviously the radiator (what's left!) After I return from the run most of the radiator is warm but not the lower half for about 6 rows in the middle. Clog? Just seems strange that a radiator would clog all of a sudden. I read about the vanes rotting off the water pump. How common is that? Is there a way to check water pump flow without pulling the pump? What is the pressure rating of the stock radiator cap? I'm going to change that and the lower hose along with have the radiator flow tested tomorrow.
 

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4Sale: 230G, U1200 Ag, 1017A, lots of MB cars, Volvo c303, 416 raildoka, LR D110 TDi
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Adam,

It never dawned on me when I was talking to you on the phone about this a couple weeks ago, but it might not actually be running hot... I have seen the temp gauge get a bad connection and show hotter than the truck is on a few diesel mogs. It is usually something that just happens one day, then continues on a regular basis. Try getting the temp up to 100 and tapping on the gauge face with a screwdriver handle... A couple Mogs I had with gauge problems would drop back to normal if you tapped on the gauge. It might be worth getting an actual read with an infired temp gauge or moving the connections around on the temp gauge once the temp is up and see if the reading drops.

Once the flow rate is confirmed, that should rule or confirm the water pump and/or radiator. There should not be a cold spot in the radiator, but that should not just cause the heat to go up all of a sudden, more of a gradual type thing.

I think the radiator cap is a 16 psi unit, but i will check my manuals and let you know.

Cheers,
Ben
 

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Discussion Starter #3
That is one thing I was thinking too but forgot to mention. I did notice on the guage that the reading is dependent on electrical load. When I switch on the headlights or other consumer the reading goes up a bit. Basically less voltage on that circuit. I have a spare autometer coolant guage from my VW and was thinking of a temporary hookup to see if the temp actually is going up. Any insight on the idea of fuel quality. Unless it's just a coincidence the truck has only done this on this one tank of fuel.
 

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Discussion Starter #4
just did a bit more tinkering today. I had the pressure washer out for the boat and the mog was right there so I gave the rad a blast. Put some actual coolant in instead of the water I've been running the past couple days for testing. Went for a drive and filled up the tank with fresh fuel from a different station. (6 cents more than my normal station!) No change. While driving I gave the guage thing a thought but I really don't think thats an issue. While driving around town in traffic the temp reads normal. Straight horizontal gauge. Once I get it onto open road and start cruizing is when the temp goes up. Slow back down at lights and if I'm there long enough the temp comes back down. While cruising at high temp I pulled over and pulled off the grille to feel around. I underestimated the cold spot on the rad. About 20 percent of the middle bottom of the rad is cold. Upper tank is HOT lower tank is warm. The truck isn't really running that hot but it's just different behavior than it used to do. The temp never goes abouve the line that is the 3/4 mark which I think is 100. But right now the temps are mild and the mog is unloaded. I plan to tow on hot days and would like some head room. I think a re-core is in my future. Or at least a rodding out but the core shows some signs of seepage so I think I should just do it for the peace of mind.
 

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1975 Unimog 406
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My 406 ran hot after a radiator recore. I replaced the t-stat (drilled a 1/16" hole in it for air to escape), flushed the heat circuit, drained the radiator, filtered the removed coolant (was new when I replaced radiator) and added water wetter to coolant and refilled. Temps went from 95-100c to 80-85c (where it used to be). Also check the surge tank lines (even inside the tank) for obstructions. Also, make sure the entire system is purged of air.
 

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mogless, except for my friends MB4-94. And a bunch of other diesel junk.
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My 406 ran hot after a radiator recore. I replaced the t-stat (drilled a 1/16" hole in it for air to escape), flushed the heat circuit, drained the radiator, filtered the removed coolant (was new when I replaced radiator) and added water wetter to coolant and refilled. Temps went from 95-100c to 80-85c (where it used to be). Also check the surge tank lines (even inside the tank) for obstructions. Also, make sure the entire system is purged of air.
All excellent advice. I had a big v8 in an old Landcruiser years ago, and found that redline water wetter was good for 10 degrees less on the gauge, as the stock rad wasn't realy big enough. Use some quality coolant flush and you'll probably be amazed at the amount of crusties that get washed out.
 

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Discussion Starter #7
Due to the big cold spot I just pulled the radiator today. There was over a liter of water that would not drain out the bottom. I had to tip it over to fully drain it and the stuff that came out was pretty murky considering I've flushed the truck with the heater hose T and a garden hose about 3 total times. I'm pretty sure there was no air in the system. I will toss in some water wetter as it helped me in other cars. Right now I'm trying to decide between a re-core of this one or a custom aluminum. Preliminary investigation seems that an aluminum might be cheaper due to the price of just the raw metal required to make the core for the original. On another note after looking closely at the fan shroud it appears that it was slightly altered for a larger radiator at some point. It looks about 3" taller than original. If anyone wants pictures of an SBU without a radiator or fan assembly now is the time. I'll snap some if theres interest.
 

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Discussion Starter #8
A bit of an update. I got the new radiator in yesterday. Man is this thing beautiful! It really is a piece of art. I'm very impressed with the craftsmanship. The guys at Tapp inc. built it for me. It is a 2 row. The rows are I think each 1.25" the total core is about an inch thicker than the old one and has more fins also. It's a tad taller but clears the hood by about half an inch. I'm quite confident in it's cooling capacity. The total was 610 with shipping which I thought was very reasonable.

While the radiator was out I ran a garden hose through all available ports but didn't get much crud out. I had already flushed a lot before. But it still runs hot.:D Not as hot but still more than when I got the truck. I'm not sore about replacing the radiator because it needed to be done anyway. I was just hoping it would cure the issue.
I have still not put a real gauge on it (I had the wrong sender) I did check the connections to the stock gauge and they seem good. I cleaned the contacts for the fuse which powers it. I guess the only things left (if indeed it is running hot and it's not just the gauge) are that I'm making too much heat or not moving enough water with the pump.
The EGT gauge is mostly installed. I just have to drill in the probe and its done. That will tell me if I'm overfueled. I just don't see how all of a sudden it would be overfueling?
It's not that I'm lazy (well maybe) but is there a way to see if I the pump is good without pulling it? I get good heat in the cab and both the upper and lower hoses of the rad are hot.
Thanks to whoever has the attention span to read all that and also for any further insight. I know I should have done the gauge first but I'm a slacker. :thumbsup:
 

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1986 U1200 / 424
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Over the winter I flushed my radiator several times using the Prestone super flush [citrus based similar to the MB treatment], replaced the thermostat, replaced all hoses, now running new coolant @ 50% mix, etc. My radiator is clean and visual inspection of the observable rows when changing hoses lead me to think the core is ok – not clogged. The drain coolant when flushing was rusty but I flushed with distilled water many times and the system was draining clear when I went to antifreeze.

I have only owned / run my Mog in winter conditions and with the warmer temps of recent I have noticed what I believe may be new worrisome engine temp behavior on the gauge.

While driving around on level country roads [no stops] with ambient temp around 60 deg F, my temp gauge reads normal, or what I assume to be normal -- a straight horizontal indicator. If I begin running wide open in top gear or hit extended grades while staying in the upper gears at 2000+rpms, my temp goes up, generally to the upper indicator line [the unlabeled one, not the 120 c top mark]. At this point I chicken out / pull back on the throttle as I don’t want to find out if the mog stabilizes here or keeps creeping up for a fun-filled surprise.

As mogstick described, if I hit level terrain or slow down / run in some lower gears the temp comes back down. Downhill running at this point can even cause the gauge to drop below the straight horizontal to a fair degree.

When the mog is idling and the gauge is horizontal, I used an IR meter and see that my upper tank is generally hotter [150 F] then the lower tank [75 f].

I have not run uphill and followed up with an IR reading on the thermostat housing. I am wary of doing this.

My question is, are the gauge readings I am experiencing ‘normal’ or might I have an issue such as a clogged radiator? I used the IR meter along the front radiator rows but could not draw any conclusions as the readings varied more vertically than horizontally. My radiator has vertical rows so I suspect the radiator is flowing well enough [when I measure it] in that the vertical temp drop would seem sufficient to control engine temps and does not vary to widely across the horizontally [therefore no plugged rows – at least for the front most core?]

I’m looking into getting a manual temp gauge, fitting to the plug on the coolant rail near the thermostat housing or the one nearer the firewall. I am interested in knowing what coolant temps measure at these locations would be considered normal under such conditions.
 

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1977 416 Danish Cargo Truck
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Maybe put a multimeter on the temp sensor? If it's got the wrong resistance for a known temperature, that would give you a bad reading on the gauge. That's a standard diagnostic procedure fore VAG products anyway.
 

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U1300L Turbo x 3
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It's entirely possible you have something like your engine timing off, so under load at max rated speed you have high EGT and the engine temp reflecting that temporarily.

My first hunch is a clogged radiator. Is the temp out of the heater super hot when you're doing that climb of doom?

Many cheap multimeters come packaged with a thermocouple probe. You could zip-tie or tape the probe to the radiator or appropriate location to get an independent temperature reading while operating. (http://www.sears.com/craftsman-digital-multimeter-with-auto-ranging-11-function/p-03482334000P?prdNo=1&blockNo=1&blockType=G1)

Another possibility is to climb your grade, get the temp high like you've been experiencing, then pull over and keep the truck at a fast idle and measure the radiator tank ends.

You could have a bad water pump too.


Over the winter I flushed my radiator several times using the Prestone super flush [citrus based similar to the MB treatment], replaced the thermostat, replaced all hoses, now running new coolant @ 50% mix, etc. My radiator is clean and visual inspection of the observable rows when changing hoses lead me to think the core is ok – not clogged. The drain coolant when flushing was rusty but I flushed with distilled water many times and the system was draining clear when I went to antifreeze.

I have only owned / run my Mog in winter conditions and with the warmer temps of recent I have noticed what I believe may be new worrisome engine temp behavior on the gauge.

While driving around on level country roads [no stops] with ambient temp around 60 deg F, my temp gauge reads normal, or what I assume to be normal -- a straight horizontal indicator. If I begin running wide open in top gear or hit extended grades while staying in the upper gears at 2000+rpms, my temp goes up, generally to the upper indicator line [the unlabeled one, not the 120 c top mark]. At this point I chicken out / pull back on the throttle as I don’t want to find out if the mog stabilizes here or keeps creeping up for a fun-filled surprise.

As mogstick described, if I hit level terrain or slow down / run in some lower gears the temp comes back down. Downhill running at this point can even cause the gauge to drop below the straight horizontal to a fair degree.

When the mog is idling and the gauge is horizontal, I used an IR meter and see that my upper tank is generally hotter [150 F] then the lower tank [75 f].

I have not run uphill and followed up with an IR reading on the thermostat housing. I am wary of doing this.

My question is, are the gauge readings I am experiencing ‘normal’ or might I have an issue such as a clogged radiator? I used the IR meter along the front radiator rows but could not draw any conclusions as the readings varied more vertically than horizontally. My radiator has vertical rows so I suspect the radiator is flowing well enough [when I measure it] in that the vertical temp drop would seem sufficient to control engine temps and does not vary to widely across the horizontally [therefore no plugged rows – at least for the front most core?]

I’m looking into getting a manual temp gauge, fitting to the plug on the coolant rail near the thermostat housing or the one nearer the firewall. I am interested in knowing what coolant temps measure at these locations would be considered normal under such conditions.
 

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1986 U1200 / 424
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To my knowledge a bad water pump is an issue if it leaks coolant or the bearings go and it locks up altogether. I’ve dealt with open loop water pumps on the outdrives of boats that are made of rubber and seal tightly in a pump housing allowing them to pull water up from below the level of the motor into a heat exchanger or the engine block itself. But on a mog, would the water pump be considered good as long as it’s not locked up or leaking?

Also the heater output does not feel extra hot when hitting the high gauge readings.
 

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'76 1300L,HE351CW,H15P Winches,Konis,Hydraulics,All Gears,10mm Plungers,Aftercooler,Lots of Littles
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Adam,

It never dawned on me when I was talking to you on the phone about this a couple weeks ago, but it might not actually be running hot... I have seen the temp gauge get a bad connection and show hotter than the truck is on a few diesel mogs. It is usually something that just happens one day, then continues on a regular basis. Try getting the temp up to 100 and tapping on the gauge face with a screwdriver handle... A couple Mogs I had with gauge problems would drop back to normal if you tapped on the gauge. It might be worth getting an actual read with an infired temp gauge or moving the connections around on the temp gauge once the temp is up and see if the reading drops.

Once the flow rate is confirmed, that should rule or confirm the water pump and/or radiator. There should not be a cold spot in the radiator, but that should not just cause the heat to go up all of a sudden, more of a gradual type thing.

I think the radiator cap is a 16 psi unit, but i will check my manuals and let you know.

Cheers,
Ben
This is my vote as well. My truck did this. Just replace the gauge with an Auberins RTD and be done with it. Those gauges are flaky as crap.

C.
 

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85' U1300L Holset Turbo VA A/C, 66' Propane 404.1 rock mog, 1975 416 Doka, G500, Volvo C303
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Do not trust the stock gauge. It is wrong!!

Water pumps can fail in several different ways depending on the design of the pump. Some failures may not be visible from the exterior.
 

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1986 U1200 / 424
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I’m going to risk a series of tests tonight and report back. I’m eyeing the VDO manual temp gauge – I’ve had one some years ago and it was very helpful – no electrical power needed whatsoever, seemed very accurate. I suppose it’s possible that my water pump is eroded from rust – my flush water was not really looking very healthy in the beginning, or in the middle of the process… yea it was actually pretty bad.
 

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85' U1300L Holset Turbo VA A/C, 66' Propane 404.1 rock mog, 1975 416 Doka, G500, Volvo C303
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The auber gauge is accurate to +\- 1 degree and comes in 24V. It also has an alarm.

Best buy you can make for price and use ability.
 

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1987 u1300L Ambo
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190 Posts
This is my vote as well. My truck did this. Just replace the gauge with an Auberins RTD and be done with it. Those gauges are flaky as crap.

C.
I had the same issue last week. Driving home from XP camper, 65mph steady speed (CLAAS), few hills. Everything seemed totally normal, and I was humming smoothly at 2200 rpm.

Noticed my Temp guage was up near 100 and kinda 'jumpy', whereas previously it moved up the temp spectrum smoothly, now it was kinda erratic between 95-100. Previously I ran 82c pretty much all the time, occasionally close to 90 on a long hill climb. But the temp change was slow and gradual.

After the initial incident, I pulled over, checked everything out. Let er cool down then started back. After that, with sustained 2200, or any hill climb, it quickly climbed to 95-100, and would come back down quickly when I let it idle.

I flushed the radiator, no crusties at all. Thinking its probably the guage, and was going to get the Auberins. I really dont know how the temp monitering guage works, any advice on installing one of these?
 

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U1450L DOKA
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If you don't have an EGT gauge yet, I'd suggest getting one installed first. While you are in
The gauge installing mode, you can install a water temp gauge as well. The easiest way is to use the original sender location, updating it with the sender that comes with the new
Gauge. Your original temp gauge goes dead, but if it wasn't accurate, then no loss. There
Are ways to add a gauge and keep the original working, but it requires a little more work.
 

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1987 u1300L Ambo
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190 Posts
If you don't have an EGT gauge yet, I'd suggest getting one installed first. While you are in
The gauge installing mode, you can install a water temp gauge as well. The easiest way is to use the original sender location, updating it with the sender that comes with the new
Gauge. Your original temp gauge goes dead, but if it wasn't accurate, then no loss. There
Are ways to add a gauge and keep the original working, but it requires a little more work.
The EGT was my next order of business! ;) Would you recommend an Auberins on that as well?

Where is the original sender location on the coolant temp guage? Total newb question, its just a system I havent gotten into yet.

Starting to feel the pressure, I'd planned to have opened everything before we go, but that date is fast approaching.
 

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U1450L DOKA
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I don't have any experience with the Auberins Gauge,but if the two gentlemen above vouch
For it, I would trust their opinion.
The sender for the stock water temp gauge is up front, next to the Thermostat housing on the front, top, driver's side of the engine. It is really the only wire in that area.
There is a thread on here regarding the installation of the EGT gauge. I did it before the turbo, which is recommended as being more accurate than after the turbo.... I drilled and tapped it without the engine running, used grease on the tap, and drill, and then snuck a small flexible tube hooked up to a shop vac down the manifold to patrol for any shavings that got away. I used Autometer gauges, but as long as the gauge is from a reputable manufacturer, you should be good to go.
Once you get the EGT gauge installed, I think you'll find your eyes going to that one first and always.
 
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