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Diablo Coolant Temp


Dave M.
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Hi All,

 

My Diablo has always been "hot-blooded" on the coolant side of things in ambient temps much beyond 75 F (basically half the year here).

 

The symptoms persist in that, while it will stay between 95-105 C is light throttle applications, and stop/go traffic, any kind of "sporting" use of the loud pedal will get a swift and rather disconcerting reaction from the coolant temp gauge. I took her out the other day for some local canyon driving and at 85 F I saw here go from 95 C to 115 C in about 45 seconds of 3000-5000 rpm 2nd gear switchbacks, no significant elevation changes (Live Oak Canyon for you South OC people). I was part throttle, never went to redline or camped high rpms and had my eye on the gauge the whole time, basically conducting an expirement after having done the following:

 

Thermostat checks (opens/closes properly)

All new coolant lines

New coolant with high temp weather mix + water wetter

New coolant temp sensor

No apparent leaks

Many burps to clear air out of coolant system

Both fans run and seem to be pushing a strong radiator exhaust flow (no rpm or cfm data to be objective though, but given these symptoms come on at 40-60mph pulls I would think the fans are marginal at that speed range?)

Radiators *appear* to be OK from exterior

 

None of the above has changed the behavior in warmer temps (80-85 F, low-mid humidity, I will not even take the car out at 90+ right now). Now a 70 F it takes a while to really manifest this same behavior and it comes back under control much quicker, so ambient temp is definitely a factor.

 

Interestingly, oil temp never broke 85-90C, and seemed rock solid the entire time once warm. Meanwhile the damn coolant gauge appeared to be directly connected to the throttle on the way up, and then needed a good amount of light throttle application / low rpm high speed cruise to go from 115 back to 90-95.

 

I was first thinking, maybe the coolant gauge isn't calibrated properly, but with how the damn thing moves I just don't see that being the ultimate answer.

 

I am starting to think: Radiators. Either there are issues I can't see with them (corrosion inside or bent fins I didn't see), or the car is woefully inefficient if everything is indeed in full working order, in which case I would love to hear if anyone has done an aftermarket radiator install? I realize without front-mounted radiators that the Diablo isn't going to be a (modern) Porsche in terms of coolant temp stability/performance in demanding conditions, but I am expecting at 80-85 F that the car isn't going to run to near red-line coolant temps in under 60 seconds of part throttle fun either.

 

Thoughts before I go off and buy a pair of radiators of some sort?

 

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Hi All,

 

My Diablo has always been "hot-blooded" on the coolant side of things in ambient temps much beyond 75 F (basically half the year here).

 

I recommend replacing the thermostat. It may appear to be working but it may not be opening 100%. Get a new thermostat ($$$) and compare the two side by side. When I first got my car I did this test and found the old thermostat was only opening about 75%. My symptoms were not as bad as yours. I was seeing coolant temperature creep towards 100C in stop and go traffic.

 

One way to test the efficiency of the cooling system is to start the car with a cold engine, turn off the A/C (econ mode) and let it come up to temperature. When the coolant temp goes above 85C the fans should turn on. The temp should start to climb down again and the fans should turn off. The temps should cycle between 80-90C. If the fans go on and stay on your system isn't working right. This test will also show if your gauge is working right as the fans are set to turn on at 85C.

 

Another test is to cruise in 5th gear at 70mph. The temps should stay near 80C. Even on hot days. I do see the temp rise quickly on hard throttle. But never above 100C.

 

In last year's Italian Stampede temperatures where near 100F in the central valley. My coolant was below 90C with the A/C blowing cold. So there's nothing wrong with the design of the Diablo's cooling system.

 

 

 

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Get a laser temp reader and check the temps on the upper and lower coolant pipes by the engine and see if it matches your gauge. If your temp coolant temp is staying that high for real, your oil temp will get hot too. If you're oil temps are staying fine, then I'm not trusting the coolant temp.

 

Could also be a bad ground to the coolant gauge. Could try jumping the coolant gauge ground with another ground.

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I have seen many thermostat issues with Diablos over the years. This would be first thing do.

 

You can remove the inner portion of the thermostat so it will flow water all the time and use it for a test. It will take longer for the engine to warm up but then you can see where temp runs at.

 

Do not just remove the thermostat as this can let the coolant flow to fast just remove the portion of the thermostat that opens and closes. Will not be able to reinstall after removal you will need a new one.

 

Or get a new thermostat and test the new one. drop is in a pan of water that is 200 deg. F and make sure it opens all the way.

 

At the dealer ship we can use LDAS to read what the coolant temp reading to the LIE ECUs is and compare to what the reading for the gauge is. The LIEs and gauge have different temp sensors. 3 sensors.

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Thanks all for the suggestions! Will take a close look at everything mentioned.

 

Jeff I will be in touch, I've been meaning to swing by to meet you. I also should probably check if there are any outstanding campaigns on the car or software updates etc!

 

Have a great 4th everyone!

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