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  #1  
Old October 19th, 2015, 09:55 AM
LR Max
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Thomason, Max
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Oil temp issue

So I was cruising down the interstate yesterday, doing about ~60ish mpg. The 2.25 gasser is running at operating temp. Suddenly, the oil temp starts dropping and drops from 85C down to 30C. I'm still hauling on the interstate, but ambient is high 50F. Coolant temp drops a little bit.

I come to stop and go traffic, and the coolant temp drops significantly (normally when I come to a stop, the coolant temp raises just a bit before falling).

What would cause my oil temp to drop like that, but keep the coolant near the operating temp? This is an Ex-mod 109. The oil temp is capillary and the water temp is electric. I do have the air-to-oil oil cooler installed as well.

Any thoughts on what would cause my oil temp to drop?

Thanks guys!
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  #2  
Old October 19th, 2015, 04:15 PM
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Keith Armstrong
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Ahh, the rest of the story

There's a thermostat in the original MoD oil cooler circuit...I have no idea if the fail-safe is open or closed...if it's "open", well that might be your answer.
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Old October 19th, 2015, 04:18 PM
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Yes, maybe the oil cooler thermostat got stuck open.
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  #4  
Old October 19th, 2015, 04:50 PM
LR Max
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So I'm looking at a drawing of said oil cooler system:



I assume part 624095 is the t-stat? I hope its full of crap or something and just needs a good cleaning. I bet there isn't one on a shelf anywhere in the US and if it is, then its worth its weight in gold.
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  #5  
Old October 19th, 2015, 06:40 PM
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That drawing does not show a thermostat per say, 624094 is a relief valve, so unless there's a differant system the relief valve could spill at higher pressures to allow cooling, should be able to clean that no problem.

Edit, looking at the position of that valve in the drawing is it backwards?? Or I'm I seeing tings
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  #6  
Old October 21st, 2015, 04:57 PM
LR Max
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On the series trucks, the oil cooler replaces the oil pressure relief valve. So any "over pressure" (for a lack of a better term) oil, instead of getting dumped back into the crankcase, gets pushed through the oil cooler.

I have a feeling has failed/stuck and is causing the issue.
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  #7  
Old October 21st, 2015, 06:04 PM
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The 109 Military setup does not have an oil cooler thermostat.
It is a bypass oil cooler as well, meaning it cools some of the oil all the time and all the oil some of the time, but does not cool all the oil all the time.
Also the oil that flows through the oil cooler bypasses the oil filter.
My guess is that your gauge reading is faulty which you can verify with a thermo-laser temp gun.
The 624095 is part of a check valve assembly.
The oil pump in you engine has the same relief valve as any 2.25 and is not oil cooler dependent in any way.

Your cooling temp rising and then falling is the normal cycle for the cooling system thermostat.
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Old October 22nd, 2015, 10:55 AM
LR Max
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Question: The gauge is capillary. What would be partial-failure mode for this?

The gauge still provided a reading. So what would cause a partial failure?

Also the coolant temp, I agree it does rise and fall, but this was lower than usual.

Stupid unreliable rover gauges. Can't decide if its telling the truth or not!

My plan is to look at the check-valve assembly, see if it is stuck open and thus, flowing too much. Also I'm due for an oil change so I'll change the oil. Possibly a partially blocked oil filter would raise the oil pressure? Dunno, just a thought. BTW I'm running a spin-on oil filter conversion. Its got a Purolator spin on oil filter on it right now.
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Old October 22nd, 2015, 11:35 AM
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Quote:
Originally Posted by LR Max View Post
Question: The gauge is capillary. What would be partial-failure mode for this? The gauge still provided a reading. So what would cause a partial failure?
According to the diagram in post 4, the gauge is electric, but you should know.
Assuming the capillary tube has no leaks, then not sure why the oil temp reading is low.
Where is your capillary tube bulb located?
There were 2 different locations, in the oil pan, in an adapter connected to the oil flow lines.
If the bulb is located in the oil pan, you have a low oil level, or your gauge is failing.

Quote:
Originally Posted by LR Max View Post
Also the coolant temp, I agree it does rise and fall, but this was lower than usual.

Stupid unreliable rover gauges. Can't decide if its telling the truth or not!

My plan is to look at the check-valve assembly, see if it is stuck open and thus, flowing too much. Also I'm due for an oil change so I'll change the oil. Possibly a partially blocked oil filter would raise the oil pressure? Dunno, just a thought. BTW I'm running a spin-on oil filter conversion. Its got a Purolator spin on oil filter on it right now.
You could replace the gauges... PM me for some options, can hook you up with some of the suppliers I use.
The bypass oil cooler has a lot of restrictions, so too much flow is probably impossible.
The check valve does NOT regulate flow, it prevents drain down.
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  #10  
Old October 23rd, 2015, 10:04 AM
Tom109
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Tom P.
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Quote:
Originally Posted by rdavisinva View Post
The oil pump in you engine has the same relief valve as any 2.25 and is not oil cooler dependent in any way.
Is this correct?

From what I have read and inquired on the Series 2 Club forum, the oil pump relief valve plunger and its helical compression spring are the same - both military and civilian applications. But the hex plug that secures the relief valve assembly differs dimensionally, resulting in different spring compression (rate) and therefore different oil pressure and flow.

This came from discussion many years ago when I fitted a 2.5d spin-on filter housing to my 2.25p and considered switching to the 2.5d's thermal control valve to feed the oil cooler.

Tom P.
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  #11  
Old October 23rd, 2015, 02:15 PM
LR Max
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Rob,

Interesting ideas. Here is the feedback I can give you:

Yes it is capillary (common on ex-MOD trucks). I did a brief inspection of the capillary tube, but I'll double check again. The bulb is located in the bottom of the oil pan. And no, the oil is not low (assuming the dipstick has no changed somehow, but I doubt that).

I agree, the cooler has a lot of restrictions and I'm sure it would have to flow A LOT of oil through it to have a significant change in temp. However that is why I am wondering if my oil filter might be clogged, because that would cause the oil pressure to rise and to seek out other "paths of lesser resistance".

My plan is to borrow a few thermocouples from work and start taking some measurements. See how accurate the gauges are. The stupid electrical coolant temp gauge has actually proven to be pretty good...somehow. I'll run it up here to the office, get to a good operating temp, then stick a thermocouple down the dipstick hole and measure the oil temp, see if I actually have an issue. Crude but should validate/invalidate the oil temp gauge.
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  #12  
Old February 11th, 2016, 03:11 PM
jcoleman
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LRMax--Did you ever come to a conclusion as to what caused the drastic oil temp swing?
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