DC controller question, temp seems high

[navyflyer72]

ok, I have a 327 (bored .060 over). An aluminum be-cool radiator, a MKVIII fan and a DC controller. I have an autometer temp gauge that takes its reading from the top intake temp probe port and the gauge is grounded to an underdash common ground. I have a 180 degree thermostat. The DC controller has jumper pins set at 16, (jumping pins 7-9). When idling the temp gauge will rise to about 200-210 before the fan comes on, I've even seen it go slightly over 210, in traffic it hovers between 190-205 and cruising on the hwy (remember outside air temp in MD right now is about 40 degrees), it will decrease to about 180. This seems high to me, can anyone explain what might be wrong, or why it is doing this? Thanks.

-George

[CAMAROBOY69]

That seems high to me too. Get ahold of Jabin (gmachinz). I will be doing this install too as soon as I finish my exhaust so I want to make sure I do it right. I have basically the same set up as you do too.

[gmachinz]

Remember that the sensor probe measures coolant temp via ambient temp. (+/-3 degrees) at the inlet-which is coolant going in through the lower hose. I suspect you have a circulation problem maybe. Your scenario tells me initially that your engine is not getting rid of the hot coolant fast enough. Is your water pump new? What kind is it? Try grounding your gauge to another source. Email me if these things don't help. Does your motor seem to heat up unusually fast given 40-degree temps outside? If so, I'd bet you have a bad water pump. -Jabin

[navyflyer72]

It does seem to heat up pretty quickly even in the cooler ouside temps. I have an aluminum stewart water pump from Vintage air that comes with the front runner system. That would really suck if that were bad, I would have to pull everything (including the radiator) out of the front again because you have to remove the entire front runner to get the water pump off... wouldn't you know it though, my freakin brand new starter was bad also, I wonder if anybody sells brand new stuff that works! As these bills get higher and higher, this is getting old. I'm gonna go take a breather for awhile before I blow a gasket.

Jabin thanks for the input, I let you know what I find out, I will sart with the ground for the gauge, oh and the relay box and surge protector showed up yesterday, thanks.

-George

[CarlC]

Don't trust the gauge. I've seen too many of them that are inaccurate. An infrared temp gun or temperature crayon will help, but a quick check would be to monitor the upper radiator hose temp as the car warms up. It will suddenly get hot when the thermostat opens. If the thermostat is opening correctly, it should be approx 180*, and your gauge should read the same.

If the temperature reading is too high you can build a resistor pack to reduce the input voltage to the gauge, but you will need an accurate method to read engine temperature, i.e. IR gun, crayon, etc.

[72nova]

I had an autometer temp gauge that was showing very high temps. I replaced it with a new one from a friend of mine. Turns out it wasn't the gauge but the cable. It was kinked at more than 90 deg. coming out of the intake. I straightened the cable and everything was fine. Maybe just a fluke but it worked for me.

[gmachinz]

George, here's another thing I just though of. Make sure the temp. sender probe isn't bottoming out inside the intake manifold-that'll give you odd readings as well. Not that this could be your problem but this is a longshot. Get an infrared heat gun as was suggested and once your engine warms up, also take a reading at the four corners of the intake or if you can, take a reading of the exhaust on each side-all of header runnrs and look for wide discrepancies. Only once have I seen a situation where with aluminum heads (brand new Edelbrock RPM's no less...) had excess slag inside the coolant passage and one head would get twice as hot as the other and the motor would only misfire on the driver's side! Edelbrock did not believe this could happen and wanted me to ship the heads back for inspection. After three weeks, I got the call that they were indeed at fault and they paid for an entire motor overhaul for the customer for the aggrevation! It was the first set they ever seen do this! Weird. -Jabin

[navyflyer72]

Thanks guys, for the input. As soon as she gets back from the shop I will try out these suggestions and see what the deal is. Some of the guys at the shop that installed the exhaust said that these engines (sbc) should run high around 190-200 to burn something off... that sounded very suspect to me. I have always heard that on the highway 180 was optimum and in the city and traffic you should strive to keep it under 200. So is there any truth to what they said?

-George

[gmachinz]

Here's the deal on running a SB at 200 degrees or so: It is primarily to burn more of the fuel contaminations (reducing harmful hydrocarbons) into the combustion process to lower emissions. The hotter the combustion chamber to a point, the more complete the burn so to speak. That does not always relate to more power, but it serves to give a more complete burn. The tighter the emissions, the leaner the fuel mixture. One way to cheat a little is by running the motor hotter. However, todays LS series motors, especially-are designed with that in mind. What motor are you building again? If you have emission checks, this might be why your shop said that. Even if that is the case, you can tune the controller for that, too. George, feel free to email me outside of the board if you need help identifying the cooling problem. You've been a great customer and I'm more than happy to help you out! -Jabin

[Damn True]

The "run it hotter" thing is something that came out of smog testing. If you had a motor that was slighty modified, or a bit long in the tooth BUT you were still subject to smog check the tip was to block off a portion of the radiator and/or install a really high-temp t-stat for the test. Get the motor hotter and the HC output would be lower. Not a way to run the car on a normal basis, but a way to skirt the smog inspectors (before they had all the high-zoot equipment they have now). Sounds like your mech may have been taught that at some point.

[baskin]

The engine temperature is usually utilized to trade off between CO and Nox. Generally, the hotter the engine, the lower the CO, but the higher the Nox. On the newer motors, the NOx is then regulated by the EGR valve, which cools the combustion.

I noticed in your original post that the temperature overshoots and then drops back down. If that’s the case, it’s probably one of four things, either your thermostat is opening later than it’s speced for, the gauge is off, you’re generating more than a normal amount of heat, or the sensor isn’t getting a good thermal contact.

If you’re using a down flow radiator, measure the engine outlet temperature with a candy thermometer and check to see what temperature the thermostat opens, this will also work on a cross flow (filler on the outlet in lieu of the inlet) as long as the fan isn’t running and a minute or two of stabilization is allowed. You can also measure byway of the fins and allow about 5 degrees for the temperature drop from the coolant to the fins.The gauge can be calibrated at the same time.

Most gauges are regulated to 5V in order to eliminate any variance from the battery voltage. The problem is that the regulator ground reference and the sensor reference can be way off if the gauge is grounded anywhere other than the engine. To verify that this isn’t a problem, let things stabilize with all of the accessories off, then turn the headlights, heater fan, and any other high current loads on and watch the gauge over the next ten seconds. If it rises any significant amount, then there’s a problem. The difference in voltage between the engine and frame can also be measured. Approximately 2 ½ volts typically sweeps the gauge, so the error will be proportional to the voltage difference divided by 2 ½ V.

If the gauge and thermostat are fine, check to see that the sensor is secure, mounted on the engine side of the radiator, and that the coolant tubes where the sensor is mounted run some reasonable distance to where they’re directly cooled by the fan.

Finally, if the fan is running at any substantial speed in order to keep the car at 190 in cool weather, there’s an abnormal amount of heat being generated. You can measure the engine inlet to outlet temperature difference. A difference of 12 degrees from inlet to outlet is typical. This could be something as simple as ignition timing, it could also be a coolant flow problem, or a leaking head gasket.

[navyflyer72]

Thanks for all the input, I will hopefully be able to narrow this down now. I will let you all know what I find out. Thanks Jabin for the compliments also, I would just hate to start bothering you solely with all the small problems I come across as I get this beast up and running smoothly.

-George

[gmachinz]

No problem, George-just let me know if you need any help. -Jabin

[CAMAROBOY69]

George,
Did you get your problem figured out? I have the EXACT same problem. Mine runs at 210. I am going to try and relocate the temp probe. Just wondering what you did or if you are just leaving it the way it is.