"Motorad" high-flow thermostats

Sorry, Norm, but that’s simply not true.

In general the higher the flow rate of coolant the more ability to remove heat from the coolant into the air through the medium of the radiator. You also need air flow through the radiator to remove heat from the coolant. This probably involves a curve which is an asymptote, whereby at zero coolant flow you get zero heat transfer to the air and as the coolant flow increases you get decent transfer but the rate of that transfer increase falls off as the coolant flow keeps increasing. You get to stage that no matter how much faster the coolant flows, even if it is supersonic, the airflow will not be enough to remove any more heat.
The art of heat transfer is not my expertise, but I can see there is a sweet spot where the relative flows of air and coolant give best result. You cannot just add more rows of tubes to the radiator to get better cooling, since that restricts airflow and is counter productive.

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Correct! It’s an agitator/impeller in a housing. It creates a pressure differential not flow.

If someone can come up with the right type of flow sensors of the correct diameter, I’ll fit them and datalog that. Then we can observe how flow is correlated to rpm and what the split at the thermostats is under various conditions. You’ll also see whether the spring loaded foot has any bearing on the outcome, even if that is just for philosophical interest.

kind regards
Marek

There are a few “urban myths” floating around.
The jag water pump,is a centrifugal pump…it is not a positive displacement pump it is a centrifugal pump. It will have a characteristic curve which essentially is a plot of flow on the bottom axis versus pressure on the veritical axis…and it will flow different litres/second depending on the restriction on the outlet of the pump…which is the discharge pressure.You can block the outlet and it will not destroy itself like a positive displacement pump will…it will flow different amounts depending on the restriction . Most pumps are rated at a fixed speed…but the XJS pump will have a series of pressure vs flow curves at each 500 rpm so the designers can investigate the envelope of performance.
The rate of heat removal in all heat exchange systems is BETTER with increased velocity of fluid being exchanged. This is a function of a critical number called Reynolds Number…which is a function of velocity…so higher velocity equals higher heat transfer.
The most important factor is surface area and speed of fluid …whether is is coolant in the radiator or air thru the fins. Armed with this knowledge the behaviour of the Jag cooling system can be analysed and understood.

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More Info!
In the August 2019 JAGUAR WORLD Q &A is a question about a XJS starting to run hotter, the car had a refreshed radiator and newer water pump. The owner was requesting help, they turned to Craig Talbot of Canada to reply. After timing and fuel he stated that 42mm stats were required to insure the bypass was completely blocked so all the flow would go to the radiator. He tried eight different brands and none except the Gates opened that far, 43mm for that brand, all the others stoped at 38/39 mm which would allow for a 3/4mm gap to recycle hot water through the engine! In my test of the MOTORAD in boiling water it does only go to 38mm fully open. So to be sure that the bypass is closed the Gates is the only one that goes past 42mm.
Now it does not have the bigger opening like the MotoRad but all the flow should be directed to the radiator, So unless you make a piece like John to block the bypass it looks like only the Gates will actually assure it being blocked!


Gates in hot water and the part #.
Dan

Waaaay back in the day, didn’t these things come with a rubber seal wrapped around that disk? I guess that’d add a mm or two to its closing length. Or am I just imagining that? I swear it’s been too long…

Has anyone actually measured the depth to the bypass port? And where do we measure it from? The bottom of the thermostat flange, or the top of the thermostat flange?

38/42= 92%.

I think in most cases, that is plenty of cooling. Maybe if you had a racing engine, would you need to insure 100% cooling.

Re-reading this, I retract my calculation. It was quite idiotic. :slight_smile:

That’s not a valid calculation. Being 4mm open is pretty much fully open. You don’t have to pull the disc all the way back to level with the thermostat mounting flange to be fully open.

I used a pair of those in my '89. Part# 33188S, which according to Rockauto is the premium version of that Gates thermostat… whatever that means.

If memory serves, no jiggle pin, I had to drill a little hole in each one. That still true with the ones you have?

Paul

I’m amazed how this goes around in circles.

Has anyone measured this and bothered reporting? Yes.
Have people acted on this by either putting a foot on their thermostats or a thicker base on the housing? Yes
Do any of you read the archives? No.
That includes the old photo albums… Oh does it?
Where do you suppose 42mm comes from?
Shall we start another thread titled "my gauge shows just past “N blah blah blah”?

kind regards
Marek

Dear Greg,

That’s terrible logic.If the average thermostat moves about 8mm open to closed, then one which only goes far enough to be 4mm short leaves you a 50:50 split not the 92% of the way there, as you thought.

Even this is poor logic though, as the 50% to the bypass is a straight 6inches easy unobstructed route back to the engine, whilst the 50% to the radiator is several feet of travel before then going through a restriction - i.e.the radiator and then coming back. Put bluntly, not being able to close the bypass is massively throwing away potential radiator (and cooling fan) capacity and loading up the water flow bias towards the bypass.

kind regards
Marek

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Kirbert,

If you look at my earlier post you will see the housing and the bypass port, I measured with that ruler, where I got the 1 5/8’s length you need for the plate to close the bypass. The MotoRad is not even to 1 1/2 so it has a gap, so did the stock one in the picture. A rubber seal would be nice if it closed the gap, but it would have to be thick. I agree that 3-4mm is a significant leak since it probably is under greater suction being so near the pump. I do not know who Craig Talbot is (are you on this site?) but he seemed to feel that completely closing the port is important.
I will put in the Gates and see what happens, although I got the 180f stats so it will not be a straight comparison.
Dan
Also I did do a search, saw nothing about the reach of the stats. Also Craig implied that the wax stats might loose some of their reach over time, maybe like the AAV going bad over time.
,

Paul,
No jiggle pin! will have to drill. I hope John will offer up a small production run so you can have the bigger opening and full range in the same stat!
Dan

Nice to read everyones thoughts/opinions.

I have used the Gates thermos also ordered from Rock Auto and drilled hole with great results both verified by needle and infrared gun.

Shortly thereafter out of my cat-like curiosity I changed them to the Motorad high flow as described above-John gave me the part number several months ago and I installed those.

I didn’t notice any thermal variance. If I had, I surely would have recorded it. I was careful to test during similar ambient temperatures.

They both worked well but now I have a nice month-old set of Gates thermostats I am trying to figure out what to do with lol.

so with one set you got complete bypass closure but maybe less flow, the other set better flow with incomplete bypass closure! I wonder if that balanced out? was the changes better than before?

Not sure how long you have been on this list.
Those of us who have been here for 30 or more years will tell you that there are no new questions or problems. Every question has been asked many times before, is some cases is slightly different contexts.
I have learned to be patient, to keep giving new list members the benefit of my experience, (the choice to accept of ignore is always up to them) because someday they will be in a position to pass on their collective knowledge.
BTW the search functions are rarely used, and this applies to virtually all discussion lists.
Don’t let that prevent you from contributing. (Smile)

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That’s a hair over 41mm, so confirms the 42mm number.

I agree with that, even though if the upper 1/3 of the radiator is completely obstructed, the B bank thermostat opening fully would result in a complete halt to coolant flow in the B bank. I would hope that an owner had their radiator serviced before it got that far, when it was only partially obstructed.

Oh, yeah, I think that’s typical thermostat behavior.

John’s little extender is starting to look like a good idea. I’m thinking, though, that perhaps a better idea (other than buying Gates thermostats) might be to construct a seat on the bypass port that raises it perhaps 4mm, thereby allowing the use of commonly-available thermostats with jiggle pins off the shelf. Perhaps a press-in thing? John?

Marek already did that way before me :wink: I chose to mount a spacer on thermostat, because it was much easier to work on a thermostat then pressing a spacer into the housing on the car and I didn’t want to mess with removing the housing.

Yes, this would be much easier.
What did you use ?
Any photos ?

Best,
Aristides