Weird Engine Coolant Temperature Readings

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disallow
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Weird Engine Coolant Temperature Readings

Postby disallow » Sat Jul 14, 2018 5:52 pm

Hey everyone!

So, its been bloody hot up here in the Winnipeg area. Bloody hot to me equals about 35C or 95F. As I've stated before, we do occasionally tow a 28 foot travel trailer. This week I towed it to a campground about 40 minutes from my house, so not far at all.

I have a Superchips tuner with Diagnostics that allows me to monitor inputs from selected OBD inputs, one of which is ECT or Engine Coolant Temperature.

Under normal conditions, I see the reading at 190F pretty much all the time. While towing the trailer home yesterday, I saw this value increase to 208-210F. It was hot out, I was going about 105kph (65MPH). It was a little windy. It never exceeded 210F. But I do not recall it ever having run this hot while towing before, it usually stayed under 200F. And for everyone's edification, no CEL codes and the temperature gauge on the dash never moved at all.

I did a quick check of the coolant level once it cooled off, and both the reservoir and the radiator are at the proper level.

Today, while not towing, and the outside temp being somewhere in the same range, 35-38C or 95-100F, I drove to Winnipeg. I noticed that on the highway my ECT reading was around 195F. Slow down for stopping, and it would jump to 198F and once we got into the city, I actually saw it get up to 205F at one point. Once again, no CEL, no movement on the dashboard temp gauge.

My question is, what is the normal operating temperature or ECT value for this truck? At my high mileage I begin to wonder if:

1. Thermostat sticking - I did replace with a Nissan Genuine thermostat and new coolant about 4-5 years ago. I am due for a coolant change, so maybe I will do the thermostat at the same time.

2. Water Pump impeller failure - Due to high mileage, the water pump may not be as efficient as it once was. I don't think its ever been changed. I got the vehicle with 100k kms on it, and I've never done it. Thoughts?

3. Pressure leak somewhere - I feel that if this was the case, it would be losing copious amounts of coolant, and it is not. Found a drippy hose clamp a few months ago, and every so often I add about 2 cups of coolant (once a year or so), so if its leaking, its not leaking very fast. Also the oil analysis I did last summer showed no coolant in the oil at all.

4. Cooling fan/Fan Clutch not working properly - I did replace the fan clutch about 3 years ago with a Nissan Genuine part. It seems to be working, so I don't think this is the problem. The aux fan also spins, usually with the AC system. I've never noticed it kick in due to high ECT reading, but I've heard other people talk about this. I do not recall the temperature threshold required for this to occur.

5. Hot air recirculation - I did replace the radiator a couple years ago. I recall stuffing the foam strips back around the rad that help it seal up to the shroud, but it definitely wasn't as well sealed as it was before. Maybe I should do a better job of sealing it...

Any other thoughts on this? Appreciate any input!


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smj999smj
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Postby smj999smj » Sun Jul 15, 2018 1:24 pm

I really don't see any problem at all. At temps near 100 degrees F., pulling a heavy load and against the wind, as well, 200-210 degree F. coolant temps aren't out of line. Keep in mind that the system is pressurized using a 16 PSI cap on the recovery tank. Every pound raises the boiling point 3 degrees F. So, the boiling point of your coolant will be around 260 degrees F., well above what your readings are. The thermostat is rated to open at 180 degrees F., so normal operating range should be in the 175-200 degree F. range.

If you are going to be replacing the coolant, replacing the thermostat isn't a bad idea, if it's original. I prefer to stick with the genuine Nissan part and the gasket is sold separately, IIRC, however, Rockauto does offer an Aisin brand t-stat, which makes a lot of the OE coolant parts for Nissan (Fuji and Sumitomo make a lot of the factory t-stats, as well). A lot of places are selling Pentosin anti-freeze, I've noticed, lately, like Autozone. Pentosin Pentafrost A2 (green) anti-freeze is what Nissan uses at the factory and what I use, mixed with a gallon of Walmart distilled water. Make sure there is no debris stuck between the radiator and condenser cores and also make sure your electric fan is working properly (I've run into a couple of Nissan electric fans, lately, that didn't work until I banged on the motor or electric fans that were turning too slowly).

As far as the radiator seals, I replaced mine when I did my radiators, but I'm sure that 99% of the people that have replaced their radiators didn't and I wouldn't think it would make that much of an issue. The VQ water pumps are, in general, very reliable. I did have a Maxima that had the shaft bearing fail and cause a lot of noise as the impeller fan hit the cover and I've seen and heard of a few that had the shaft seal fail and cause a coolant leak out of the drain hole on the side of the block, but, do to the improvements in anti-freeze over the years, you hardly ever hear about the impeller fans corroding away, anymore. Generally, if they are not making noise or leaking, I leave them alone unless I'm replacing the timing chains and have it easily accessible. If you do go that route, Hitachi makes the factory part; Rockauto offers Aisin in limited supply and I would probably go with that if I had to replace mine.

But, all in all, it really doesn't sound like you have a problem, IMO.


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