Thermostat Housing Leak

Technical advice Q&A

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jemt1234
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#1 Thermostat Housing Leak

Post by jemt1234 » Thu Nov 28, 2019 1:58 pm

When I got my etype (65 s1 FHC) , it wasn't fitted with a thermostat, so I got a new one from SNG Barrat along with a new gasket. When I install them and tighten the housing and fill with water, the water pours from the bottom of the housing.
It seems like the issue is that the thermostat is bigger than the hole in the gasket, so that if the thermostat is fitted first and then the gasket, the gasket doesn't touch in manifold.
The thermostat doesn't go into the manifold enough to be a flush fit, nor into the housing.
I could just cut the gasket to the diameter of the thermostat, but I want to know what is wrong rather than just bodging it.
thanks in advance for your help

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Heuer
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#2 Re: Thermostat Housing Leak

Post by Heuer » Thu Nov 28, 2019 2:15 pm

I think that (Land Rover) thermostat requires the housing to be machined. Maybe more info here: viewtopic.php?p=65692#p65692

and here: https://www.coolcatcorp.com/thermostats ... ifold.html
David Jones
S1 OTS OSB; S1 FHC ODB

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#3 Re: Thermostat Housing Leak

Post by jemt1234 » Thu Nov 28, 2019 2:20 pm

as I ordered it from Barratts I was expecting an etype one. so is the thermostat the wrong one?

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#4 Re: Thermostat Housing Leak

Post by Heuer » Thu Nov 28, 2019 4:09 pm

The original Smiths thermostat has not been available for years. It was a fairly unique thing with a skirt that covers the by-pass slot. The Land Rover SIIa thermostat is similar and still available but requires the manifold to be machined. There is another version that has been produced that requires no machining, the details of which you can find in the threads I kinked to. It is a complex subject so you need to read up about our findings.

The correct Jaguar part number is C20766 but it now refers to after-market examples. The original LR thermostat is a cousin to Jaguar c20766. The diameter of the full bypass shutter is 48.5mm., however, on the widely available Chinese copies, the shutter is often just 47.5mm. Unfortunately, the LR thermostat will not fit in a 3.8 housing unless the car's thermostat neck is modified. It needs to be bored out to 54 mm for a depth of 9mm. Once the neck is machined, it will ONLY accommodate a Land Rover thermostat, so it's a permanent commitment. Full details at the Coolcat link.
David Jones
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#5 Re: Thermostat Housing Leak

Post by MarkRado » Fri Nov 29, 2019 6:16 am

I file down the rim carefully with a warding file and use a good quality sealer (dirko).
Mark
1963 OTS 880436

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#6 Re: Thermostat Housing Leak

Post by abowie » Fri Nov 29, 2019 6:58 am

I just use a generic 75*C thermostat that fits. Seems to work.
Andrew.
881824, 1E21538. 889457..oops
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#7 Re: Thermostat Housing Leak

Post by Heuer » Fri Nov 29, 2019 1:40 pm

it will fit but will not work as Jaguar intended. May as well run without one rather than mess with the poppet stat!
David Jones
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#8 Re: Thermostat Housing Leak

Post by abowie » Sat Nov 30, 2019 4:09 am

Heuer wrote:
Fri Nov 29, 2019 1:40 pm
it will fit but will not work as Jaguar intended. May as well run without one rather than mess with the poppet stat!
I read the CoolCat page with interest, but I'm not entirely sure I grasp the finer detail still.

Where I live I can't see much point in the small bypass circuit as it's never cold enough here to slow the engine warming up.

If a thermostat is restricting flow maybe I really am better off without one? Or if I do use a poppet one should I use a 7lb cap to up the boiling point?

Calorically Confused in the Colonies.
Andrew.
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Tom W
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#9 Re: Thermostat Housing Leak

Post by Tom W » Sat Nov 30, 2019 8:55 am

Firstly, unrestricted flow is bad. Don’t run without a thermostat, you’ll never get the car to warm up.

If you don’t want a thermostat, then you need to replace it with a bung with a hole drilled in. To size the hole will require some experimentation, and then you’ll only have the right cooling for the ambient conditions on the day you get it right. Race cars sometimes run this setup (presumably for reliability), but then racers do a lot that doesn’t work on a road car. So, for a road car, you want a thermostat.

The function of the thermostat and bypass seems very miss understood. It’s not an on/off switch that opens part way through warm up and stays open for ever more. It’s a feedback loop to maintain a steady engine temperature. It works as follows:

Imagine the engine is up to temperature. The thermostat is open, and water flows into the top hose and through the radiator. The water is cooled by the radiator. The amount of cooling is dependent on radiator efficiency, the amount of air flowing over it, and the temperature of the air flowing over it. So there is now cool(er) water entering the water pump from the bottom hose, ready to pass through the engine again. The engine has no control over how cool this water is, that’s down to radiator efficiency and ambient conditions. Imagine it’s very cool by the time it reaches the water pump. After it’s lap round the engine, it reaches the thermostat where it’s still not warmed to operating temperature. This cooler water causes the thermostat to close, shutting off the top hose and opening the bypass. The cool water now passes directly back to the water pump for a 2nd lap around the engine. This time round, it reaches the thermostat above operating temperature, so the thermostat opens again, and so the feedback loop continues. In reality it’s not so exaggerated, the temperature doesn’t fluctuate, and the thermostat adjusts as necessary to maintain a constant temperature.

Now, e types, and other old cars, suffer because the rad doesn’t always have the capacity to over cool the water, so the thermostat is pegged wide open and the temperature continues to climb.

If you fit a thermostat that doesn’t block the bypass when it opens, you’ll always get some water that doesn’t pass through the radiator and the car will be more likely to overheat.
Tom
1970 S2 FHC

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#10 Re: Thermostat Housing Leak

Post by steve3.8 » Mon Dec 02, 2019 11:16 pm

Jemt1234,

Yes i also bought a sleeved stat a while ago, even though i was advised against.
Nowadays it seems almost compulsory to have to check and inspect that goods can be fit for purpose.
My car ran too hot with the sleeved stat,so i ordered a replacement from Robey's.

Below is a comparison between a £25 :thumbdown: :thumbdown: sleeeved stat and a £6.77 + vat Robey supplied C27650 74 degree stat that comes in a Jaguar branded box, the gasket is £1.50.

Below is a photo of the test i did, both stats are fully open , the sleeved stat does not open as far and the main flow is further restricted by having to pass through the quadrant slots as per your second photo in post 1.
I drilled 2 x 5mm holes in the Robey base plate , positioning 1 @ 12 o clock when fitted.
The operating temperature is now correct.

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:wavegreatbritain: Steve3.8

64 3.8 fhc, 67 4.2 fhc

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#11 Re: Thermostat Housing Leak

Post by abowie » Tue Dec 03, 2019 12:03 am

OK. So if I understand correctly, I need to block off the bypass slot with a sleeve and use a regular thermostat with either a bypass or a couple of holes in it?
Andrew.
881824, 1E21538. 889457..oops
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#12 Re: Thermostat Housing Leak

Post by MarkRado » Tue Dec 03, 2019 4:47 am

I didnt experience any problems with the sleeved one.
Mark
1963 OTS 880436

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#13 Re: Thermostat Housing Leak

Post by steve3.8 » Tue Dec 03, 2019 9:19 am

abowie wrote:
Tue Dec 03, 2019 12:03 am
OK. So if I understand correctly, I need to block off the bypass slot with a sleeve and use a regular thermostat with either a bypass or a couple of holes in it?
I have'nt blocked the bypass slot , the Robey Jaguar stat is a blank base plate without a toggle bleed , the reason for the holes is to help air bleed and reduce the running temperature a couple of degrees,
The original factory rating was 70 degrees opening and 75 fully open .
The sleeved stat i tested was not fully open until 78 degrees ,combine that with its restricted flow .

Not good !
:wavegreatbritain: Steve3.8

64 3.8 fhc, 67 4.2 fhc

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#14 Re: Thermostat Housing Leak

Post by abowie » Tue Dec 03, 2019 10:39 pm

Andrew.
881824, 1E21538. 889457..oops
http://www.projectetype.com/index.php/the-blog.html
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#15 Re: Thermostat Housing Leak

Post by abowie » Tue Dec 03, 2019 10:45 pm

Just doing a little maths.

So if the bypass slot is 1/8" high and only 2" long then that's an area of 0.25 square inches. The Coolcat article above quotes an orifice area of between 0.78 and 1.0 square inches through an open thermostat. So if I use a non sleeved thermostat I'm potentially getting in of the order of 25 to 30% of my coolant bypassing my radiator.

Does that sound correct? If it is I really need to address it. Where I live I don't have any problem at all with the car warming up, but efficient cooling is an absolute must.
Andrew.
881824, 1E21538. 889457..oops
http://www.projectetype.com/index.php/the-blog.html
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