Engine coolant temp good proxy for oil cooler fan switch?

[Joel Heinke]

This is the related question to the other thread about best location for oil temp sensor.

Given the mid-engine location in my Miura and that there's no real external air intakes close to where the oil cooler/radiator will be located, I've elected to use an electric fan to enhance the oil cooling. One of the disadvantages I've heard about remote oil coolers is that in cold weather oil temps can remain below optimal and/or it can take a long time for oil temps to come up to the desired range. So ideally the fan should only come on when oil temps are up in the "goldilocks zone".

The ideal answer would be to add a temperature sensor in the oil system that would trigger the oil cooler fan. Alternatively, there's an output from the Holley Terminator X ECU being used in the car that's meant for controlling engine coolant fans. It's programmable so the fan can be triggered for different coolant temperatures. I know that engine coolant temperatures and oil temperature are only somewhat related but my question is if they are closely enough related that a common sense answer for controlling the oil cooler fan could be to use engine coolant temp as a proxy? For example, when the engine coolant as measured for EFI control reaches 185 degrees will the oil temperature likely be high enough that the oil cooler fan won't be keeping the oil from warming enough?

I'm asking as where possible it's nice to take advantage of in place items and not add additional potential points of failure. Not that an additional sensor is all that risky but there's the additional wiring that needs to run by hot things like headers that could be avoided by using the existing ECU wiring. There will be a oil temp gauge in the car so I could try it and if oil temps stay too low put in a specific sensor for the oil cooling fan.

I'm curious as to other peoples thoughts on this topic so specific reasoning is appreciated in responses.

 

[Brian]

If you can boolean the water temp with high RPM and throttle position and have it stay on 5 minutes that might work. I know megasquirt can do this, but don't know about your Holley. Otherwise, it'll either run all the time or not at all. Water temp stays pretty well regulated by the thermostat, and it's fluctuations are not that well correlated with oil temp.

I know you don't want this answer, but best practice would be a thermostatic switch that turned the fan on when oil got over 225 or so in the sump. A probe tied to the pipe going into the cooler, insulated from ambient air would be second best.

 

[Joel Heinke]

So here's another bit of information about the Miura. It is equipped with a Davies Craig electric water pump (EWP) controlled by a dedicated coolant sensor and their controller. There is no thermostat in the coolant system but the controller is suppose to keep the coolant temperature steady to the programmed settings by varying EWP speed from off to full speed. I anticipate it will take longer for the engine coolant to come up to temp versus a standard thermostat controlled system as there is a lot more coolant to warm up given the 1.5 inch pipes from engine to radiator at the front of the car. If this turns out to be the case, I'd anticipate the time between cold start up and when the ECU thinks it needs to turn on a coolant fan to be a decent amount of time and maybe enough to have the oil fully warmed up by then.

As is probably evident, there's several "newer things" at play here and thus why I'm trying to solicit input. I'm anxious to get the project to a point of engine startup and trial as a "go-kart". I'm working on getting wheels to make it a roller to get to that stage.

 

[Fred W Ballinger]

Do you not have space for an oil thermostat rather than trying to control a fan?

oil thermostats

 

[JP Verweij]

So here's another bit of information about the Miura. It is equipped with a Davies Craig electric water pump (EWP) controlled by a dedicated coolant sensor and their controller. There is no thermostat in the coolant system but the controller is suppose to keep the coolant temperature steady to the programmed settings by varying EWP speed from off to full speed. I anticipate it will take longer for the engine coolant to come up to temp versus a standard thermostat controlled system

With the Davies Craig system & no factory thermostat it actualy takes less time for the coolant to come up temp. The DC ECU controls the EWP flow temp related.

 

[Brian]

Here's another thing to consider.

With no belt driven waterpump to circulate the water, it's critical to sense the temp where it will get a good read without flowing water, like in a head instead of at the water in the front of the engine. (I seem to remember you having an LS)

Otherwise, when the engine and water are stone cold, the off engine temp sensor will remain stone cold, and until the pump kicks on and that's all it will ever see, even as the engine is boiling down.

Chevys with heater deletes like Mopar and Ford can do cause boil over problems because they rely on the heater circuit rather than a bypass hose to move warming water around the block of a cold engine, and the heat never makes it to the thermostat, so it never opens.

 

[Joel Heinke]

Do you not have space for an oil thermostat rather than trying to control a fan?

oil thermostats

I have thought about using an oil thermostat (and likely can find the room for one) but I'm more concerned about the high heat side versus the warm up side. In other words, I think a oil cooling fan will be needed even if an oil thermostat is used because of how tight everything is in the engine compartment. So I don't think it's one or the other on these two items. Given the cost of an oil thermostat, I think I'll wait to go there until it's clear that one is needed in order to keep the oil temps up in the desired temp range.

 

[Joel Heinke]

With the Davies Craig system & no factory thermostat it actualy takes less time for the coolant to come up temp. The DC ECU controls the EWP flow temp related.

That's good to know. The engine is a Gen2 Coyote and the water pump has been completely removed and replaced with the DC EWP system.

 

[Joel Heinke]

Here's another thing to consider.

With no belt driven waterpump to circulate the water, it's critical to sense the temp where it will get a good read without flowing water, like in a head instead of at the water in the front of the engine. (I seem to remember you having an LS)

Otherwise, when the engine and water are stone cold, the off engine temp sensor will remain stone cold, and until the pump kicks on and that's all it will ever see, even as the engine is boiling down.

Chevys with heater deletes like Mopar and Ford can do cause boil over problems because they rely on the heater circuit rather than a bypass hose to move warming water around the block of a cold engine, and the heat never makes it to the thermostat, so it never opens.

The coolant sensor for the electric water pump is installed in the coolant neck on the outflow from Coyote engine:

I was told by the Davies Craig folks that their EWP controller pulses the EWP on cold startups such that the warming coolant is cycled out of the block and thus to where the sensor is located. I don't have first hand experience with this yet (still working to get to initial startup) but in theory it should avoid the situation you've described.

 

[Brian]

That should work. Even without the EWP pulsing, just the tiniest bit of bubbling should create enough movement to get hot water to the sensor. Especially without a thermostat blocking the path. Some old tractors relied on the percolation rather than a water pump.

 

[Joel Heinke]

I'm leaning toward using this item, Derale Part Number 35022 (just over $40), installed upstream of oil radiator for fan control. Nice compact unit, -10AN fittings, handles up to 15 amps, turns on at 180 degrees and off at 165. The fan I have draws just under 7 amps so it shouldn't require a relay. It might turn out to be even simpler than using the coolant fan signal from the ECU which would require adding a relay.

Has anyone used one of these for oil cooler fan control? Did it work without any issues?

 

[Howard Jones]

Two things:

The first thing is I have the same EWP system as you and a mid-engined car with a radiator up in the nose. Engine output is 430-450HPish. Put the coolant temp sensor used to control the EWP controller at the hottest point in the coolant system. This will usually be high up on one of the heads or on a crossover point between the heads. The engine will heat up at a rate that would be the same as a closed thermostat if the pump does not come on. Without circulation, the water in the heads gets hot very fast, so wire the pump so that when the engine is on the pump is powered up. With the pump off the water temp in the radiator and nearly all of the rest of the coolant circuit will remain at ambient while the water in the heads goes well above 250F and turns to steam. It's all about the coolant temp at the location of the sensor as it relates to what the controller is doing as well as the target temp you set. It will not turn on and cool the engine if it doesn't see coolant temps above the target temp. At least that is how my DC EWP controller works. Maybe the newer models do work as you describe but I would not rely on that because it still needs an accurate real-time coolant temp to CONTROL coolant temp.

Second. I like this kind of sensor housing better. You can select oil temp on/off and there are a lot of options for both hose sizes as well as on/off temps. I would use the an10 with 210F on and 195F off. Your temp sensor above is too cold IMHO. My target temp for oil is 210-220F and constant with no spikes above 230F which will keep the oil in good condition and not damage it. This is basically what I made to avoid all the adapting and save a little money for my oil temp gauge sensor housing. Mine is 1-inch diameter pipe with AN10 weld on male fittings on each end and a hole in the side threaded for the sensor.

https://www.amazon.com/dp/B085VR831D/ref=sspa_dk_detail_1?pd_rd_i=B085VLMD5B&pd_rd_w=7pzHb&content-id=amzn1.sym.dd2c6db7-6626-466d-bf04-9570e69a7df0&pf_rd_p=dd2c6db7-6626-466d-bf04-9570e69a7df0&pf_rd_r=C6XRF0YWSK49D86WFXCN&pd_rd_wg=hJdOw&pd_rd_r=255617f8-afa8-461c-831e-1a38ddb64965&s=automotive&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWxfdGhlbWF0aWM&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExN0RVRDc4Nk5XRTMwJmVuY3J5cHRlZElkPUEwOTg1MTk5MzQ1SkIySklMTDZJOCZlbmNyeXB0ZWRBZElkPUEwODE4MjIwNjY0WVlPVVlHMzJaJndpZGdldE5hbWU9c3BfZGV0YWlsX3RoZW1hdGljJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ&th=1

Yours will work but I would be sure the sensor probe does not restrict oil flow through the fitting. AN 10 is a minimum oil line size IMHO. I think I would use the AN12 sensor port and adapt the ends to AN10 with something like these just to be sure not to restrict flow. Or use AN12 oil lines if you like.

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Do you intend to install a oil temp gauge? I would. You could also consider adding a temp sensor bypass/fan manual on switch just because its easy and a good backup for cheap/offshore sensors. I would also use a relay for the fan motor. I don't think these sensors like the current spikes associated with dc motors turning on.

I can't wait to see how your car comes out. It is very interesting and a great build. Good luck.