L28T runs too cold? (SDS users please look)

[Nigel]

I searched the archives, and found lots of posts on overheating, but not much with regards to "under" heating. I have 240Z with an L28 Turbo engine and SDS EM3-6F system. Watching the engine temperature on the display, I see the following:

 

62C (143F) - highway cruising in the fall

70C (158F) - highway cruising in summer

75C (167F) - idling in traffic

80C (176F) - after hot restart (never seen hotter and it quickly goes back to 75C)

 

Those temperatures seem to be on the cool side, and from what I picked up from the posts I read in the archives, hotter is better. I wondered if perhaps I had installed a 72C (160F) thermostat way back when, and not a 82C (180F) thermostat like I thought. Now that my Z is off the road for the winter, I pulled the thermostat out, and I do have a 82C thermostat in there (genuine Nissan, if that means anything).

 

Now I'm confused. I thought that the temp rating on a thermostat is it's opening temp, so 180F would be the lowest temp I would expect see, not the highest right? So, why is the engine apparently running so cool (20C cooler than thermostat rating)? And the thermostat is not stuck open. For the SDS users reading this, what are the typical ET's you see on the display, and what thermostat are you using?

 

Thanks!

 

Nigel

'73 240ZT

[Kennysgreen280zt]

My SDS reads just about the same way. Ive also got an autometer water temp gauge which reads a little higher. The E-type we SDS'd at work does the same thing. I think with the 180 T-stat you should be fine. Later

 

Kenny

[Drax240z]

My temp on the SDS and my autometer gauge read the same. Your temps do look a bit low to me. Where did you install the sensor? I put mine in the lower thermostat housing.

 

Are you using a large radiator? What kind of coolant fluid mixture?

[Nigel]

Thanks guys...

 

I have the sensor in the lower thermostat housing. I'm using the 1/8 NPT Dale sensors, not the GM ones. The rad is a recored 280ZXT unit, with a 50/50 mix of coolant and water. I have a 280ZX fan and fan clutch. I also have an RX-7 thermostaticaly controlled oil cooler. No oil temp gauge in the car yet though (winter project).

 

I guess it could just be that the readings on the SDS display are not all that accurate. I guess they don't really have to be. But to be out by 20C or 40F seems excessive. Today, I'm going to put the thermostat in a pot of water on the stove and measure the opening temperature with a digital cooking thermometer.

 

Nigel

'73 240ZT

[savageskaterkid]

Mayb u have a bad thermostat, they do crap out eventually-my frends toyota supra just had the same problem, it would run too cold-turns out that his thermostat broke and stayed in the open position-wich let the cool coolant get in the engine, b4 it was hot-he put a new thermo in-gave it about 3-5 minuts, and the temperature went up in no time

BUT, i did NOT overheat

[Nigel]

I just tested the thermostat in a pot of water on the stove. I monitored the water temp with a digital cooking thermometer, and the thermostat opens around 85C. I continued to heat it up to ~100C and then let it cool down to see the closing temp and it closed at 80C. So, the thermostat operates as one would expect. Based on this, I would expect that my ET reading would be 80C minimum, not maximum. This leads me to believe that the ET reading is is not accurate. However, when the engine is cold, the ET reading is pretty close to atmospheric temp, and it matches the air temp. Perhaps the sensor is somehow being cooled? The SDS Dale temp sensor is just a thermistor glued inside a 1/8 NPT plug with a hole drilled partway through it.

 

Hmmmm.....

 

Nigel

'73 240ZT

[jkube]

Hi Nigel,

 

Is there something with the SDS that requires a correction factor to be put in place if you dont use the prescribed sensor?

 

I have the Megasquirt installed using the 280zx coolant sensor ( Megasquirt defualt is GM sensors), and I definately had to put in a correction factor for this.

 

Made the car run much better.

[Nigel]

jkube:

 

The 1/8 NPT Dale (no idea why they're called that) sensors were supplied with the unit, and the ECU is configured specifically for them before the ECU ships. The engine runs fine. It just concerns me that if the display is going to show engine temperature, it should be accurate.

 

Nigel

'73 240ZT

[Tony D]

It probably is accurate, but watching a test pot is a lot different than the actual flowing temperatures you might encounter during running the vehcile.

 

My Megasquirt shows my engine running at 160 at idle, and it WILL NOT get any hotter unless I am driving the vehicle under a load! Now I have a 160F thermostat, but as soon as some load goes on it, the thing goes right to 170 where the 160 thermostat is fully open. But only if it's good and hot outside. During cold weather, the thing will fight to get to 160---which is why I usually flush and rethermostat in the winter... As long as your oil temperature is above 180 (and should be as it normally runs a delta above water temperature of at least 20 to 25 degrees) you should be fine for proper lubrican action.

 

I wouldn't sweat it, people will say it should run "Hotter" but if you change your oil regularly "sludge" should not be a problem as you get near enough to 180 watertemp (meaning 200, 215 oil temp). Oil temperature is the real thing to worry about.

I made sure all my warmup bins were satisfied by 155 degrees, so they are definately no in play while I'm driving. That would be more of a concern to me than the actual runnigntemperature of the engine. My oil temperature rarely if ever gets below 180 even at idle, so that is proper for lubricant action. And prevention of water buildup and contaminant cookoff at that temperature is acceptable. Ideally during a highway run you would probably get closer to 225, to 240 degrees, and boil out all the water, and flash off the gas. They want at least 180 oil temp to flash gasoline and alcohols out of the oil. Water, well it will slow boil at that temp, and make a nice brown pudding...

 

Now if you can check your oil temps---THAT would make an interesting discussion!

[Nigel]

Maybe I'm just making a big deal out of nothing. But I really like to understand these things, especially when they seem counter-intuitive. The temp sensor is right next to the thermostat. How could the temp at the thermostat be any different? I don't have any background in thermodynamics, but my inuition tells me that two things in such close proximity should be the same temperature. Assuming that the display is correct, and the temperature of the water at the sensor never goes above 80C in normal driving, then the thermostat would never open, or at the most, open just a tiny crack.

 

If this is the case, then that would mean that in everyday driving, the radiator isn't even necessary to cool the engine. This leaves air cooling of the block, and/or oil cooling. As I mentioned, I do have an RX-7 oil cooler which is quite large. It's thermostaticaly controlled, but I don't know the opening temp off hand. I did test the thermostat before installing the cooler and it worked ok then. Unfortunately, I don't have the oil temp gauge installed yet, so I don't know if the oil temps are ok or not.

 

I wish I could remember what my ET's were at the track day I ran at this past summer. I remember my Air Temps averaged around 50C. I seem to recall that the stock water temp gauge was slightly above half way (it's usually at half or slightly below).

 

Interesting... I wonder if I can figure out a way of verifying the SDS display temp without running the engine (I've got a bunch of stuff pulled apart to install an electric rad fan - Christmas Present).

 

Nigel

'73 240ZT

[stagefumer11]

my l20et runs only just on the low cold mark, and moves up to 1/4 the gauge when thrashing it. would this mean it runs to cold. i do notice when its warmer outside and it sits on the 1/4 mark i get much better low down torque, how can that change that ?