Engine pre-heater?

[folivier]

Well since we've been down in the 20's I thought this would be a good time to see if the pre-heater works. I'd tried it previously when temps got down in the 30's but couldn't tell if it made any difference when starting the 8v92. Yesterday I booted up the laptop, started VMSPC and turned on the ignition. The engine temp showed 58, hmmm, it was about 28 outside. Rebooted the laptop, still showed 58. Figured maybe a sensor might be bad. Today I tried again, engine temp showed 60, outside temp was about 32. Engine fired right up. Thought maybe the preheat light was burnt, nope that works. Maybe the solenoid is stuck on to the receptacle where the Kimstart is plugged in. Nope, no power there. Makes me think that maybe there is another pre-heater that has a thermostat to only turn on when temp is below freezing? Guess I'll have to look around more to try and find it. I do have the 3 electric heaters in the coach and the 1 in the water compartment running.
Any ideas? Guess I shouldn't worry when something seems to work right, but I just like to know.

[fulltiming]

Do you have either a Aqua-Hot or Primus system in use? If so, you may be heating your engine off of the diesel/propane system.

[folivier]

No aquahot or primus, just the electric heaters and raritan water heater going.

[fulltiming]

Unless someone has added an additional form of pre-heat, I would tend to go with your first guess, that the temperature sensor is wrong. How does the dash engine temp gauge compare with the VMSPC when the engine temp starts to get up around 100 degrees? The dash gauge and the VMSPC are feed off of separate sending units, one on each side of the engine. Trouble is the dash gauge bottom number, at least on my coach, is 100 degrees.

[Bill N.Y.]

If you plug your coach in, you might have an electric block heater wired in that you are not aware of.

If you are plugged in, unplug your coach for 24 hours and recheck to see if it is still reading higher temps than ambient.

60'ish sounds about right for an electric block heater at 28 degrees.

[fulltiming]

Also remember that temp senders are calibrated over a specific range. You want your temps to be most accurate at about 200-210 degrees. However, that said, a 25-30 degree error at 32 is more than I would expect.

It is also possible that the engine heat transfer manifold for you water heater is having some affect but again, it shouldn't be 25-30 degrees.

[chockwald]

You must be getting heat from a source other than the pre-heater. I've only got one source, and that is the block heater. Without my blockheater, my 6V92 will not start at sustained temps under 40 degrees. Had to use it a lot on our Pacific Northwest trip between Thanksgiving and Christmas. Typically, if I left it on all night, the dash gauge would read just over 100 degrees. I don't have VMSPC, so the analog gauge is all I have. One thing I learned the hard way is that if the block heater has been on, or is on, don't loosen the radiator cap....the heat, obviously, creates some pressure. You can guess the rest....

[encantotom]

i have spent a lot of time on calculating thermistor curves as i calibrated my dash mounted digital engine coolant/engine temp gauge.

the spec's on the panasonic thermistor that i put one each of on each side of the block has spec's that go from 40 degrees C to 125 Degrees C. so, the low side of the spec is about 100 degrees F. however they use a baseline calibration temperature of 25 degrees C for a resistance of 1000 ohms.

a thermistor is inside the temp senders and it is a resistor that varies in resistance with temperature. the resistance goes down with an increase in temperature. the relationship is very nonlinear. the resistance below 25 degrees C (75ish F) is very inaccurate on mine and i assume most of them.

here is a general scale for the thermistor for the senders i have put in.

Resistance Reading F

1000 ohm 74-78
100 175-179
50 215-219
30 248-252

so, in other words, i wouldnt use the temp senders as a gauge for actual temp. could be accurate i guess for lower outside temps, but certainly not on mine.

would be much easier to use a temp gun and shoot it...

btw, because the temp senders i got were off in calibration, i built a resistive network of variable adjustable resistors and have had darlene tuning them with a microscrewdriver as i drive. i have one zeroed in and the other one almost there. they are wayyyy not accurate at temps when the engine isnt running.

i have the acutal thermistor part number of the senders i put in if anyone wants it and or the temp curves and charts.

it ends up the way i calibrated (i have a single digital gauge on my center console and i use a rocker switch to move between temp senders on the left and right bank of the 8v92) is that i used the DDEC2 temp as the reference temp as i have compared it to everyone elses as i have driven with them and i believe it to be accurate. then i just at a steady temp, adjust the ones i have (try to do it at 180-185) to match it.

not very scientific, but the only thing i could figure to do.

the digital guage basically is an ohmeter that measures the resistance, then has a memory chip inside the gauge that has a lookup table of all the temps vs resistance and it looks up the resistance, and puts that temp number on the gauge. it has about a 10-15 sec delay so it isnt in actuality instantaneous.

i just quickly checked my digital gauge (not the vmspc) and with an outside air temp of 58 degrees, the gauge read 80 degrees.

so, in other words, i would guess that your vmspc is not showing the actual temperature. so i would also guess that actually you are not heating anything up. the starting right up thing i cant comment on. i could also be wrong, but can only guess based on my experience with these thermistors.

not sure you wanted all that, but you got it. take it for what you paid for it.

later

tom

[Richard and Rhonda]

Uh what Tom said. Put your hand on the block and see if it's warm. That will tell you if something is providing heat or it's a sensor calibration issue

[folivier]

Guess I'll have to buy a fancy infrared thermometer (Santa musta missed that one on his list). Cranked it up today and it cranked up quick, watched the temp on VMSPC come up to operating temp. Can't see where there might be another pre-heater (no wires visible). Guess I need to block it up and crawl underneath.
Thanks to everyone for the suggestions.

[encantotom]

the block heater on mine is clearly visible from the passenger side engine compartment door. just follow the electric cord that is plugged in the outlet on the firewall.

if you had one on, it would be drawing some serious amps on the ampmeter you have up front.

tom

[folivier]

Well there is only one pre-heater a Kim Hotstart and I got it working today. The thermostat was bad so I just bypassed it. They sell the same models with or without a thermostat. After reading on Kim's webpage it seems the thermostat is only needed when an engine is on stand-by and needs to be available to start anytime. I figure I'll only use the pre-heater once or twice a year. I like these cheap fixes.