eugene Posted September 3, 2001 Share Posted September 3, 2001 Pursuing an idea regarding temperature senders and would like opinions. Especially interested in PParaska's opinion after looking at his website. I took resistance measurements of both Datsun and Chevy temp sending units from 120 to 200 degrees. They are both Negative coeficient (As temp increases, resistance decreases); however, the resistance decreases at different rates. Unfortunately, the chevy sending unit has higher resistance than the datsun unit, so simply adding a resistor would not work. But, by adding a resistor in parallel, the circuit resistance could be lowered. I worked some numbers and found that, theoretically, if a 62 ohm resistor is added in parallel to the sending unit circuit using the stock chevy sending unit(78 truck 350), then the gauge should be extremely accurate from about 180 to 190 deg. F. and right on the money at 185. Due to the different rate of change in the chevy sending unit, the gauge would read hotter than actual temp at 190 and above, and lower than actual temp at 180 and below, which is I believe not bad since the gauge would be accurate where it counts and at the same time would catch your attention quicker if things started to heat up. The basic idea is that you want to drop the resistance in a series circuit. By adding a resistor in parallel you split the amperage and effectively lower the total circuit resistance. Another benefit of this could be that resistors could be easily used to tune your gauge: Accurate temp. measurements could be taken with a known good piece of equipment like an infared pyrometer, and the correct resistor could be selected to precisely reflect this temperature on your gauge. Any ideas, has anyone tried something similar? Quote Link to comment Share on other sites More sharing options...
Guest empracing Posted September 3, 2001 Share Posted September 3, 2001 nice idea that sparky training may just come in use after all gotta love that Quote Link to comment Share on other sites More sharing options...
Dan Juday Posted September 3, 2001 Share Posted September 3, 2001 I appreciate your work on this Jason. I'm in a predicament right now over this very issue. I installed my motor before addressing where I would install the sending unit. Now I'm stuck. I have no other good place to put it but in the side of the head where GM put it. But, on later motors, (mine is a '91) the hole is 3/8 npt. I made the adapter per JTR, but I can't find a 45/64" drill bit short enough with a 3/8" reduced shank that will fit between the head and the shock tower. This motor came out of a well running wreck and I don't want to pull the head to do this. Plus, I'm lazy. That's a lot of work! Lets get the brain trust on this board working on this problem. There must be an easy way to put a thermister in that circuit that would work. Or, If anyone knows where I can get drill bits made to order, cheap? Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 3, 2001 Share Posted September 3, 2001 How about this... A small piece of steel tubing the size of the radiator hose. Weld a bung on the tubing for a temperature sender to screw into. Cut the radiator hose, install the temperature sender tube between and clamp it up, add water and serve. It would seem to work anyway. Perhaps not as quickly as in the engine block though, but then again I watch my gauges ALOT (maybe paranoia...) Regards, Lone PS: If you were to use tubing, giving the edge a tap with a hammer over the edge of a vise or anvil will flare it a bit so the hoses won't pop off. I made my own exhaust collector pipe doing just that. A bead roller does this the best, but not many have those at home. (I will someday...) [ September 03, 2001: Message edited by: lonehdrider ] Quote Link to comment Share on other sites More sharing options...
Mike C Posted September 4, 2001 Share Posted September 4, 2001 I guess that could be done in the lower hose, but I don't think it would be very accurate. Regardless, I think the sender needs to be before the thermostat. Otherwise a defective t-stat could cause the engine to overheat but not register high on the gauge? Anyone? If you are willing to assusme that the thermostat is working (reasonable assumption) then you can get a t-stat housing that is tapped for senders. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 4, 2001 Share Posted September 4, 2001 I had the same prob - needed a non-Datsun sender but wanted to keep the original gauge. I simply went to an auto electrician that specialized in instruments & he had a specification book on senders. He looked up the std. Z one, looked at the thread/diameter I needed & was able to find one that had near as dammit resistance ratings with the correct thread. I plugged it all together, no probs she works. I also had a 0-120 deg. C bulb thermometer, so I (carefully!) checked the water temp. in the radiator at the radiator cap. This then gave me confidence with what I was seeing on the gauge. Not super accurate I agree, but I believe I'm getting consistent readings, and I know when the car's getting too hot. The needle also normally sits just under half-way across the gauge. Quote Link to comment Share on other sites More sharing options...
pparaska Posted September 4, 2001 Share Posted September 4, 2001 Jason, it sounds like you figured it out and know where the down falls are and that you can live with them. Dan, I didn't have holes in my head ( ), so I put my temp sender in the intake manifold, in a hole already provided. Quote Link to comment Share on other sites More sharing options...
eugene Posted September 4, 2001 Author Share Posted September 4, 2001 I guess I'll keep toying around with it. Hopefully I'll have it running in a month or so and will let everyone know if it works. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 5, 2001 Share Posted September 5, 2001 My heads are 1994 Corvette aluminum D ports. I used the 3/8" adaptor from a Stewart Warner direct read capillary type water temp gauge. All I had to do was drill out the center slightly to accomodate the OEM Nissan temp sender and the OEM jam nut from a Z screwed right in. These types of capillary gauge adaptors use a tapered seat compression seal just like the OEM Nissan temp unit uses. Small world huh. Hasn't leaked a drop in six years. The adaptor kit is available seperately from NAPA. You will get a lot of parts you don't need, but the kit doesn't cost much, and plus you don't have to drill on the head. Remember that both the bullet and male spade connector type sending units will work. I prefer the bullet style. I simply put a good quality high temp silicone spark plug boot over the wire to protect it from the #8 cylinders header pipe. Accuracy is as good as it gets. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 5, 2001 Share Posted September 5, 2001 The specific adaptor kit I used was manufactured by a company called "EQUUS" Part no. C730-400-57 SKU no. 0-47923-06851 The kit contains four adaptors of various sizes. Idaho Z Car. Quote Link to comment Share on other sites More sharing options...
Dan Juday Posted September 6, 2001 Share Posted September 6, 2001 Idaho, please don't be offended for me asking this, if you are sure about this the adapter must look like a helicoil. The Datsun coller almost screws into 3/8 npt. Are you sure it's not 1/2 npt? I'm taking those part #'s to Napa tomarrow. I hope you're right. You'll save me a ton of work! Quote Link to comment Share on other sites More sharing options...
Dan Juday Posted September 7, 2001 Share Posted September 7, 2001 Idaho, Sorry for doubting you. I bought it today at Napa! $5. After looking at it I now understand. Yes I did have to make some minor adjustments, easily done on the drill press. Thank you, thank you, thank you. You saved me work and money. That's important to me because, as I've said before, I'm cheap and lazy. Quote Link to comment Share on other sites More sharing options...
Mike Mileski Posted September 7, 2001 Share Posted September 7, 2001 Jason, I just did the parallel resistor thing on my early Ford Bronco, 1969, that I put a SEFI '91 Mustang motor into. Even using the stock Bronco sending unit, I couldn't get the stock gauge to show the proper normal running temperature, about 190 degrees. I wired in a 20 ohm resistor in parallel, and now it reads where it should. I know its not as accurate at lower temperatures but, who cares? Mike Mileski Tucson, AZ Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 9, 2001 Share Posted September 9, 2001 Why couldn't you drill and tap the runners on the intake manifold on either of the two sides of the thermostat housing? Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 10, 2001 Share Posted September 10, 2001 Some manifolds have an undrilled "raised" area on the coolant runner to allow you to do just that. If your manifold doesn't have such a raised pad, the wall thickness may not lend itself to good purchase for the threads which means poor sealing and coolant leaks. It the attempt fails, you have no way except welding to repair the damage. Keep in mind that temp sensor units MUST be constantly bathed in the coolant in order to read accurately. The heat transfer from air is not the same. Sensors located high up on the manifold will read cold if the coolant level drops below them. You literally could be completely out of coolant and the gauge/sensor will not show an overheat situation until it is way too late. The ideal position for coolant sensing in my opinion is as high in the heads as you can get without running the risk of uncovering the sensor in the event of even a minor coolant loss. I have a rotary switch which allows me to use one gauge to sense temps in both heads and at the top of the radiator. I merely switch between the gauge and ground (sensor) points. I did this because consistency in the drag car is dependent on consistent engine temps from run to run. When I began paying attention to details like this at the track, my car's predictability went way up, as did my win/loss ratio. Each motor responds differently to temp as far as HP output. With a little experimenting you can find valuable HP increases. Quote Link to comment Share on other sites More sharing options...
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