350SD Running cool, but is it too cool? - PeachParts Mercedes-Benz Forum

Blevinsax · #1 10-29-2006, 02:27 AM

I've taken these two quotes from another current thread (Got_The_Benz's thread "Thermostat.... @ Thermostat...) in an effort to avoid hijacking that thread.

Quote:

Originally Posted by t walgamuth

if your car is routinely running significantly under 80 then you need a stat.

Quote:

Originally Posted by ncof300d

Temperature has an effect on fuel economy. I ran my '85 300D last winter with it never reaching 60C. Fuel economy was 22-23mpg. I put in a new thermostat and the temperature stays between 85-90C. My worst case has been a 2.5mpg improvement.

I'm trying to come up with the best solution to a possible similar issue in my 350SD. I am happy to report that the temperature problems I had earlier this summer (upwards of 115CC) are gone, but now the car is running so cool that I am wondering if it is TOO cool. It will usually make it up to 80C eventually with some extended driving, but often it tops out at just 75C on my regular daily drives. It typically runs smooth, even moreso on WVO (the subject of another of my recent threads @ Smooth idle on WVO / Vibration at idle on B20... Why?) so I am wondering if I have a thermostat problem since it is running so cool.

Since the car is running so cool, should I just be thankful and let it go - or should I be concerned about it running too cool? I have read some of the possible consequences of running cool - fuel economy, carbon build-up, etc.

I am not too concerned about fuel economy because I am running on WVO, but that is also part of this equation - I need to be sure my WVO is hot enough, and my WVO is heated by coolant in my GreaseCar system. I am, however, concerned about carbon bulid-up, particularly after reading sixto's recent thread on 3.5 bent rods (3.5 bent rod?) in which he concluded that caron build-up might have contributed to the bent rod in his 3.5L. I have already removed my EGR and had the intake manifold cleaned out, so hopefully I will not be building more carbon from the EGR. I also want to be reasonably confident that I am not building more carbon from under-heated WVO.

Here are two possible ideas - please tell me what you think, particularly if you have another idea:

1. New thermostat allowing my engine temps up to 90C. Then coolant would be hot enough to sufficiently heat WVO, but this means my engine is running 90C consistently.

2. A VegTherm to electrically heat WVO. This way the WVO is up to sufficient temps, but the engine is still running lower temps.

The ultimate goal for me is the long term health of this motor combined with the ability to run WVO. I appreciate everyone's input, advice, experience, and opinion!

1985 300SD Sady · #2 10-29-2006, 08:34 AM

Quote:

Originally Posted by Blevinsax

I've taken these two quotes from another current thread (Got_The_Benz's thread "Thermostat.... @ Thermostat...) in an effort to avoid hijacking that thread.

I'm trying to come up with the best solution to a possible similar issue in my 350SD. I am happy to report that the temperature problems I had earlier this summer (upwards of 115CC) are gone, but now the car is running so cool that I am wondering if it is TOO cool. It will usually make it up to 80C eventually with some extended driving, but often it tops out at just 75C on my regular daily drives. It typically runs smooth, even moreso on WVO (the subject of another of my recent threads @ Smooth idle on WVO / Vibration at idle on B20... Why?) so I am wondering if I have a thermostat problem since it is running so cool.

Since the car is running so cool, should I just be thankful and let it go - or should I be concerned about it running too cool? I have read some of the possible consequences of running cool - fuel economy, carbon build-up, etc.

I am not too concerned about fuel economy because I am running on WVO, but that is also part of this equation - I need to be sure my WVO is hot enough, and my WVO is heated by coolant in my GreaseCar system. I am, however, concerned about carbon bulid-up, particularly after reading sixto's recent thread on 3.5 bent rods (3.5 bent rod?) in which he concluded that caron build-up might have contributed to the bent rod in his 3.5L. I have already removed my EGR and had the intake manifold cleaned out, so hopefully I will not be building more carbon from the EGR. I also want to be reasonably confident that I am not building more carbon from under-heated WVO.

Here are two possible ideas - please tell me what you think, particularly if you have another idea:

1. New thermostat allowing my engine temps up to 90C. Then coolant would be hot enough to sufficiently heat WVO, but this means my engine is running 90C consistently.

2. A VegTherm to electrically heat WVO. This way the WVO is up to sufficient temps, but the engine is still running lower temps.

The ultimate goal for me is the long term health of this motor combined with the ability to run WVO. I appreciate everyone's input, advice, experience, and opinion!

My vote is for #1. What t-stat is in the car currently?

I always thought that 90*C was the normal operating temp... that is what my car runs at most of the time.

Plus, thermostats are a cinch to replace.

Brian Carlton · #3 10-29-2006, 09:13 AM

My vote is for #3.

#3 says that you should get a non-contacting thermometer and shoot the cylinder head to see what the temp. actually is.

The calibration of the sending unit/gauge is usually the culprit when the discrepancy is a few degrees one way or the other.

AFAIK, the thermostat is rated at 80C., so, anything near this figure is perfectly acceptable.

BenzDiesel · #4 10-29-2006, 11:16 AM

I would consider that "perfect" range, not too hot AT ALL and not too cool, since 80 C, which is normal operating range for most Mercedes cars, will never contribute to a head problem, in terms of overheating or cracking or head gasket blowing, or any other heat related issue, in my opinion.

BenzDiesel

Blevinsax · #5 10-29-2006, 12:39 PM

Quote:

Originally Posted by Brian Carlton

My vote is for #3.

#3 says that you should get a non-contacting thermometer and shoot the cylinder head to see what the temp. actually is.

Brian, you're right - the first step would obviously be to confirm that what I am seeing on the temp gauge is in fact accurate. I remember now - process of elimination - eliminate obvious/simple issues first - like bad information (i.e. incorrect gauge readings.)

Quote:

Originally Posted by BenzDiesel

I would consider that "perfect" range, not too hot AT ALL and not too cool, since 80 C, which is normal operating range for most Mercedes cars, will never contribute to a head problem, in terms of overheating or cracking or head gasket blowing, or any other heat related issue, in my opinion.

Assuming the temps on my gauge are correct (which I will determine ASAP) that is the reasoning behind the VegTherm electric heat idea - I know that heat is dangerous for these motors, so if mine will run this cool and help prevent the problems associated with high temps, I would be happy to leave it as is. The only concern that presents is the temperature of my WVO since it is heated by coolant - I don't want carbon build-up as a result of running WVO that is not up to temp. If I could bring the WVO up to at least 70C with a VegTherm, then I could let the motor continue to run cool where it is - once I confirm that the temps I am seeing on my gauge are accurate with a non-contacting thermometer as Brian suggested above.

So, I have never been on the market for a non-contacting thermometer before - where should I start looking, and how much should I anticipate paying for one? It seems like a good tool to have around for lots of various reasons, so I wouldn't mind having one.

Brian Carlton · #6 10-29-2006, 12:45 PM

Quote:

Originally Posted by Blevinsax

So, I have never been on the market for a non-contacting thermometer before - where should I start looking, and how much should I anticipate paying for one? It seems like a good tool to have around for lots of various reasons, so I wouldn't mind having one.

I got a decent deal at the Tool Warehouse. IIRC, the unit was about $110 or so. There are lower cost versions without the infrared light that are down close to $60.......possibly less.

E-bay also has some good deals on them.

greasybenz · #7 10-29-2006, 04:04 PM

why dont you just go for the injector line heaters from fattywagon. Then you wouldnt have to worry about carbon build up due to the lack of coolent heat. The injector line heaters warm up to 200F in 2mins!

http://fattywagons.com/fwproducts.htm

Blevinsax · #8 10-29-2006, 07:30 PM

Quote:

Originally Posted by greasybenz

why dont you just go for the injector line heaters from fattywagon. Then you wouldnt have to worry about carbon build up due to the lack of coolent heat. The injector line heaters warm up to 200F in 2mins!

http://fattywagons.com/fwproducts.htm

This is why I can't just go for the injector heaters from fattywagon - copied from Fattywagon's site that is linked above... (See attached)

The only other option of which I am aware for electric heat would be the VegTherm - other than a DIY heater, but I'm definitely not into that.

Anyone have experience with the VegTherm to share?

greasybenz · #9 10-29-2006, 09:28 PM

WOW! didnt know that, maybe if i drive over to sacramento ill see whats going on. Maybe if they are open after i go to the meet on the 4th.

rg2098 · #10 10-30-2006, 07:00 AM

Quote:

Originally Posted by Brian Carlton

.....AFAIK, the thermostat is rated at 80C., so, anything near this figure is perfectly acceptable.

I could have sworn the spec for normal operating temp was 83C.

Ara T. · #11 10-30-2006, 07:16 AM

The amount of money you spend on one of those thermo-gun dealies you can get like 6 thermostats. So just get a new Behr and pop that sucker in. It will be better for the engine. Another thing it helps is the amount of time it takes for the engine to warm up. It will be drastically shorter, at least for me it was. My old stat would keep my engine at 65 degrees or so and wouln't go much higher unless it was a hot summer day with AC on. I don't know how bad your stat is though. Does it take a long time to get to 75 degrees?

MattBelliveau · #12 10-30-2006, 08:06 AM

Quote:

This is why I can't just go for the injector heaters from fattywagon - copied from Fattywagon's site that is linked above... (See attached)

I wish they would have posted that BEFORE I dropped $200 with them a few months back

(issue resolved of course).

Blevinsax · #13 10-30-2006, 12:32 PM

Quote:

Originally Posted by Ara T.

The amount of money you spend on one of those thermo-gun dealies you can get like 6 thermostats. So just get a new Behr and pop that sucker in. It will be better for the engine. Another thing it helps is the amount of time it takes for the engine to warm up. It will be drastically shorter, at least for me it was. My old stat would keep my engine at 65 degrees or so and wouln't go much higher unless it was a hot summer day with AC on. I don't know how bad your stat is though. Does it take a long time to get to 75 degrees?

Yesterday in an approx 100 mile freeway drive it was cruising along right at 80C after about 15 minutes warm up - even went up to 90C on an incline (driving up a mountain at 80mph

) Last night on the drive home from a gig, my temp gauge never topped 70C all the way home. However, it was about a 5 miles drive - total of only 10 minutes. How long should it take for the engine to come up to 80C?

gsxr · #14 10-30-2006, 03:30 PM

Temp should NEVER be under 80°C. If a new t-stat doesn't cure it, replace the sender for the gauge... I've found more than one that read lower than actual. A new sender is about $10 and IMO, it really isn't worth trying to prove the old one good or bad - it's 20 years old, just replace it. If it's still under 80 after a new t-stat AND sender, then it's time for further troubleshooting... IMNSHO.

Blevinsax · #15 10-31-2006, 02:57 AM

Again today I drove the 350SD around all day and it sat pretty consistently at about 83C - with no A/C or anything, of course...

Quote:

Originally Posted by Ara T.

Does it take a long time to get to 75 degrees?

...then tonight after my gig (and after cooling down while sitting in a parking garage for about three hours) it barely made it to 70C for the drive home. When I pulled into the garage I noticed that it finally got up to just under 80C, but it was still low.

Besides this little temp issue/concern/curiosity, the car was a total pleasure to drive all day!

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