What’s “too hot” for a diesel?

[T-Cut]

The presence or absence of a bleed hole for in-line stats has a dramatic effect. In fact when the in-line system was in general discussion/adoption, it became clear that to achieve the desired improvement in running temperature, the stat should be completely watertight when closed. In fact the three or four recommended brands are stats shown to be watertight. The effect of small drillings was also investigated and the conclusion was that there should be no hole for maximum effect. The question really, is what do you wish to obtain? If an occasional rise to 100C scares the pants off you, then don't fit a higher temperature, watertight stat, use a different, less effective type or drill a 2 - 3mm hole.


TC

[75driver]

Originally Posted by T-Cut

The presence or absence of a bleed hole for in-line stats has a dramatic effect. In fact when the in-line system was in general discussion/adoption, it became clear that to achieve the desired improvement in running temperature, the stat should be completely watertight when closed. In fact the three or four recommended brands are stats shown to be watertight. The effect of small drillings was also investigated and the conclusion was that there should be no hole for maximum effect. The question really, is what do you wish to obtain? If an occasional rise to 100C scares the pants off you, then don't fit a higher temperature, watertight stat, use a different, less effective type or drill a 2 - 3mm hole.


TC

Thanks TC.
I guess I want it to operate to it’s specified operating temperature (88C), as quickly as possible, with consistency in operation.

The newly installed 88C firstline stat, with no hole drilled in it, seems to meet my expectations.

While an occasional rise to 100C wouldn’t scare the pants of me, the erratic nature of previous (also 88C) stat couldn’t be regarded as operating correctly.
Sometimes it would rise from 84 to 97 in under 10 seconds with no real engine load, sometimes stay at 87 for over 5 mins when I was pushing it on a bit.
Watching the temperature on the obd is distracting, and not something I would wish to do long term.😅


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[T-Cut]

Yes, reliability and predictability is important. Regarding 'specified' running temperature, I don't think the stat setting necessarily tells you that. Any engine can reach a running temperature somewhat higher than the stat's nominal opening point. Petrol engines do so as a matter of course. Once the stat's fully open, the radiator fan will moderate things when it goes higher. It's all a question of balance. As far as MGR was concerned, 'normal' running was up to 115C. I realise many of us would freak out well before that point, but if everything works as intended, it will cope fine. The engines have ample cooling capacity - providing the radiator fan works by the book.

In my opinion, the area that might limit the 'maximum' running temperature is the quality of the rubber hoses. Some MGR ones are on the decidedly flimsy side for running up to 22psi.

TC

[75driver]

Well, after just over a week, the firstline stat is no longer functioning correctly, with operating temp now topping out at 78 deg.
Disappointing😞


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[Heddy]

I fitted a First Line Renault 5 stat yesterday. I had to order it from a local motor factors (next day) so I specified 89 degrees. OBD temp shows 90-93 before falling to a minimum 85. This is a little more desirable than the previous 88 degree one. That cycled between 82-85.

[COLVERT]

If drilling a very small hole in the stat would you place it at high level or low level. If at high level could a bubble block it.

Would water flow through a 1 mm hole ?? How small a hole can you get away with if you just want to make sure the stat bulb gets hot water QUICKLY around it so that it opens at the correct temperature.---

[Avulon]

Originally Posted by COLVERT

If drilling a very small hole in the stat would you place it at high level or low level. If at high level could a bubble block it.

Would water flow through a 1 mm hole ?? How small a hole can you get away with if you just want to make sure the stat bulb gets hot water QUICKLY around it so that it opens at the correct temperature.---

Oh yes, water will flow through 1mm hole with ease. How much how fast

depends on the pressure in the system. Good point about possible air locks ... Except the air can pass through the hole and the water can rise to the hole if there is pressure behind it. But still a good thought to put the hole low to make it easier to flow.

[T-Cut]

Originally Posted by COLVERT

If drilling a very small hole in the stat would you place it at high level or low level. If at high level could a bubble block it.

Logic suggests at the highest point available, but it's probably irrelevant for increasing/providing a permanent flow-through of coolant. There doesn't seem to be a demonstrable reason to provide a bleed-through for air. The stat warms up through fluid turbulence and conduction of heat directly from the head.

Would water flow through a 1 mm hole?

Yes it will. But it's not 'water', it's coolant.. Coolant has a much lower surface tension than plain water so it will easily pass through small holes that standing water might not. Encouraged by the pump, there will be significant flow-through.

How small a hole can you get away with if you just want to make sure the stat bulb gets hot water QUICKLY around it so that it opens at the correct temperature.

The introduction of a bleed hole of any size negates the reason for fitting the in-line stat. It was demonstrated earlier that drilling a hole of any size decreases the running temperature while having minimal effect on warmup rate. So, the concensus is don't drill a hole in a watertight stat. The recommended brands are watertight when closed. I suspect a complicating factor is that some engines warm up more slowly than others and there's nothing you can do about it.



TC

[clf]

Originally Posted by 75driver

Well, after just over a week, the firstline stat is no longer functioning correctly, with operating temp now topping out at 78 deg.
Disappointing😞


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these two videos show the difference between one stat working effectively and one not. (the difference is small, but keep in mind there is no additional forces other than gravity. In the coolant system, there is a pump to drive the flow, as well as the additional pressure from the coolant system)

Leaking

not leaking

As TCut stated in a post previously regarding these videos, it would have been interesting to add some form of detergent to break any surface tension of the water (to simulate the effect of coolant more effectively). However I think it still illustrates the problem.

[75driver]

Well, seeing as the replacement dmgrs stat had started to fail open after only a week, I removed it and replaced with the motaquip stat (that was the reason for this thread in the 1st place).
However, this time I drilled a 1.5mm hole, as it was the smallest bit my drill would take.


For what it’s worth, I installed the stat with the bleed hole at the top of the pipe.
Bled the system, as I had done before.
- bled through the bleed screw above the fbh, by raising the tank, until a steady flow thru.
- ran engine at 2500 rpm with cap off until reached 70 deg.
- put cap on and watched temp rise
This time it only went to 87, before dropping to 86, and then rising again, at which point I took it for a spin. (Previously this stat, with no hole drilled went to 96 before dropping)
Now, having only done about 10 miles, stat is no longer operating erratically.
Cycles consistently between 84 -88, rising to 90 under an uphill load.
It will be interesting to see what warm up times are like in the morning.
Who knew you could have so much fun with stats 🤔🤔


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