Branson 3510i, new thermostat, still runs cold

[thistlemagnate]

This Branson 3510i used to run as expected, even at an idle the temp gauge went up into the normal range after a few minutes and stayed there. Starting a month ago, for no apparent reason, it stays cold, occasionally see it go to normal but then pretty much immediately heads back down. Monitored temps around the top of the engine (including around base of the thermostat) with an infrared thermometer, typically around 120F even after an hour of light work. Worked it hard yesterday with a 3 bottom plow at 2000 rpm, took better part of an hour to get up to the normal range, but then it mostly stayed there. Tried replacing the thermostat (with one bought through Branson) two weeks ago, had been previously replaced by dealer a couple years ago during a blown headgasket repair. No change with new thermostat in place, and old thermostat opens up around 180-190F in a pot of hot water. I'm about to run this thing to the dealer, but that's a major operation out here in the boonies, and we need it to get a cover crop in. Any hints?

 

[davesl708]

The temp sensor maybe coated in deposits preventing an accurate reading. Temp on the block will be lower than the actual do to convection of the metal.
Just a thought.

 

[thistlemagnate]

The temp sensor maybe coated in deposits preventing an accurate reading. Temp on the block will be lower than the actual do to convection of the metal.
Just a thought.

Thanks for the reply. I'll take a look at the temp sensor, but I don't think that will be it.
It does occasionally get up to a correct temp reading and might mostly stay there if working it hard, or soon pops back down to nothing if I am not. I read 150F at the base of the thermostat when working it hard, considerably under the ~190F rated temp of the thermostat, so your comment is largely correct. But still see 120F at the base of the thermostat after working the engine with a light load for an hour. I know this tractor well enough to know the smell and rush of warm air when it is at temperature, and it seldom gets there now.

When it does warm up towards normal it never gets any hotter than what I remember as normal. So I suspect the thermostat is opening up when it hits that normal temp as it should, and the temp gauge is reading correctly.

I think I have some minor leakage past that headgasket, in that after running the engine for a minute I will have a minor puff of compressed something if I then shut it down and take the radiator cap off. Prior to having the headgasket replaced, the headgasket leak was sufficient to pop the radiator pressure cap and blow out the water. Perhaps the head is warped a bit. The headgasket blew about 3 years ago when somebody else was rotovating on a dry dusty day, temp gauge covered with dust, and radiator got plugged with dust as well. Almost got hot enough to freeze the engine, but not quite.

I can't imagine how the engine could be running cold with a good thermostat in place, and I'm pretty sure it is correctly installed. The dealer installed the old thermostat (my hot water test suggests it is still servicable) and I installed the new thermostat, both behave the same.

 

[Stimw]

I had to replace the temp gauge sending unit on my 10 year old 3510 about a year ago. It quit reading all together.
My guess is yours crapped out and is working off and on.
Overheating probably didn't help it.

 

[thistlemagnate]

Didn't use it much over the winter, finally got back to this and figured it out.

From my post of 10-11-2015:
> I'll take a look at the temp sensor, but I don't think that will be it ...
> I read 150F at the base of the thermostat when working it hard ...
> I know this tractor well enough to know the smell and rush of warm air when it is at temperature ...

Replacing the temp sensor fixed it.
No deposits to speak of on the old one.

It's real easy to delude yourself into thinking you know what's going on.
Unlike some fields of endeavor, tractor repair insists that you come to terms with objective reality.

This temp sensor for the panel gauge is mounted near the top of the thermostat housing,
on drivers left side at the front of the engine. Easy to swap out with a 17mm end wrench.
When I snapped the wire connector on to the new sensor, it felt loose. So pulled it off and
squeezed the connector with a pair of pliers so it would grip better, maybe that's all it was.
Too bad, now I can't throw out the old sensor, thinking I might need it 20 years down the road.
If I have further trouble with this stock round one, I might solder in a flat lug connector of some sort.

There's a second temp sensor nearby, a bit below and to the right.
It has a flat lug wire connector on it. (Why two different temp sensors?)
My dealer recommends pulling that wire off of the sensor,
then the timer for the glow plugs thinks the engine is always very cold
and gives you the maximum of around 20 seconds with the glow plugs before timing out.
So once familiar with the tractor, you can better control how long the glow plugs work
before turning the key all the way to start.

 

[rasorbackq]

Didn't use it much over the winter, finally got back to this and figured it out.

From my post of 10-11-2015:
> I'll take a look at the temp sensor, but I don't think that will be it ...
> I read 150F at the base of the thermostat when working it hard ...
> I know this tractor well enough to know the smell and rush of warm air when it is at temperature ...

Replacing the temp sensor fixed it.
No deposits to speak of on the old one.

It's real easy to delude yourself into thinking you know what's going on.
Unlike some fields of endeavor, tractor repair insists that you come to terms with objective reality.

This temp sensor for the panel gauge is mounted near the top of the thermostat housing,
on drivers left side at the front of the engine. Easy to swap out with a 17mm end wrench.
When I snapped the wire connector on to the new sensor, it felt loose. So pulled it off and
squeezed the connector with a pair of pliers so it would grip better, maybe that's all it was.
Too bad, now I can't throw out the old sensor, thinking I might need it 20 years down the road.
If I have further trouble with this stock round one, I might solder in a flat lug connector of some sort.

There's a second temp sensor nearby, a bit below and to the right.
It has a flat lug wire connector on it. (Why two different temp sensors?)
My dealer recommends pulling that wire off of the sensor,
then the timer for the glow plugs thinks the engine is always very cold
and gives you the maximum of around 20 seconds with the glow plugs before timing out.
So once familiar with the tractor, you can better control how long the glow plugs work
before turning the key all the way to start.

My Branson temp gauge has never moved . I bought it with 100 hr and never really noticed it was always hard to the left.
What did the sensor cost?

 

[thistlemagnate]

My Branson temp gauge has never moved . I bought it with 100 hr and never really noticed it was always hard to the left.
What did the sensor cost?

About $30 as I recall. Could have been $40.
Good idea to have it work, you want to know if it's running hot due to dust in the radiator
or a pinhole leak in one of the hoses.

Using my trusty $1 HF digital volt meter on the old sensor, I see around 1040 ohms when at 64F,
and 120 ohms at 200F. Seems to be working. My guess is I just had a bad connection
from the wire into the top of the sensor. You might put a 100 ohm resistor from that wire to
ground (the engine block) to simulate having a hot sensor in there, see if the meter budges.

 

[Zork]

...There's a second temp sensor nearby, a bit below and to the right.
It has a flat lug wire connector on it. (Why two different temp sensors?)
My dealer recommends pulling that wire off of the sensor,
then the timer for the glow plugs thinks the engine is always very cold
and gives you the maximum of around 20 seconds with the glow plugs before timing out.
So once familiar with the tractor, you can better control how long the glow plugs work
before turning the key all the way to start.

I'd be careful with that one unless you know where the glow plug is installed in the cylinder, the glow plug's fail rate, and the type of failure (burns out, swells, or disintegrates?) of that brand of glow plug. Some glow plugs fail differently and just do not heat up and others swell or break off. Depending on the design and placement in the cylinder, when they break off it could mean catastrophic engine failure, or if they swell, you sometimes break them off when you attempt to remove them, then you have to remove the head to remove the debris.

Let us know if you find out.