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Thermostat questions

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steveg

steveg

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I'm wondering how important the sleeved t-stat is overall - especially since no-else seems to use them. Moss sells the non-sleeved fail-open MotoRad which would seem to be a better bet in the event of failure.

Does anyone have an opinion on how important the sleeve & bypass setup is in temperate or hot weather driving? Does it even matter?
 
With the non-sleeved version, some coolant is recirculated and not sent through the radiator. With the tendency of Healeys to run hot, bypassing the radiator in hot weather doesn't help. For those of us who don't like the cost of a sleeved thermostat, I installed a thermostat bypass blanking sleeve and a modern thermostat.
 
No holes; there are small ones already. I've been running it that way for a couple of years, ever since a tech session at British Car Specialists where the importance of the sleeved thermostat was explained. There is a recessed ring in the head where the edge of the thermostat rests. It was only deep enough for the thermostat lip, so I had to deepen it a bit (I have an aluminum head) to allow both to fit in and be flush with the head surface. Hope that's clear. I recall the sleeve reduced the maximum temperature by about 10F. I would run 100F above the outside temperature. Now it's like 90F above, with a minimum of 165F.
 
I"m not entirely convinced about blanking off the bypass port unless overheating is regularly experienced or the ambient temp is always high. The problem is that near ambient-temp coolant is coming from the bottom of the radiator into the engine when driving fast in cold conditions or before fully warmed up and this is not a good thing. The bypass port allows hot water from the head to blend with the cold incoming water and even up the balance to extend engine life. With the bypass port blocked off then you get only cold water into the front of #1 cylinder. All engines wear more on the front of #1 cylinder due to colder running, even with everything working right. IMO it isn't a good idea to block the bypass port unless you really have a cooling problem as it will shorten the engine life.

Modern engines put the thermostat in the bottom hose to prevent cold water entering the engine. They recycle hot water underneath the thermostat to heat the bulb and it only opens a crack to let cold water in when required. If the water coming in is hot from idling in traffic then that causes the t stat to open up.
Andy.
 
John, I know we've had this discussion before but I'm becoming more and more interested in this whole thermostat options business. Am I right in understanding that your permanent blanking sleeve does have some small holes in it so that it does allow some water to bypass the radiator but not as much as would be the case if a normal thermostat was used. The point Andy makes about extra wear is valid as well. I guess, like most things, it's a trade off. If you live somewhere with very hot summers and your car runs a little hot it might for instance make sense to run without a thermostat at all, to get more flow. There might be marginally more engine wear but as most people only drive 2000-3000 miles a year this might not be such a problem.
 
Derek, Actually, I do live where temperatures exceed 100F during the summer. At that point, I'm the one that overheats. Yes, there are small (~1/8") holes in the blanking ring so there is some coolant flow in the bypass.
 
I have the BCS modified Robertshaw t-stat with the ring soldered to it. The ring is only 1/2" tall and is a very sloppy fit in the opening - maybe 1/8" gap all around between it and the wall of the opening. Can't see how it could be very effective - especially for > $100.00.

That being said, it seems to me the use of the blanking sleeve with a modern t-stat would make the system similar to all the other cars on the road which seem to do OK without the bypass port.

My takeaway using thermostat plus Moss blanking sleeve per John T: those of us who live in hotter climes would be trading a faster warmup (no big deal - still a warmup - we're keeping the t-stat) for an ongoing more efficient cooling system which where I live would be a good tradeoff indeed.
 
steveg said:
That being said, it seems to me the use of the blanking sleeve with a modern t-stat would make the system similar to all the other cars on the road which seem to do OK without the bypass port.
Click to expand...

In 20 years of wrenching I have yet to see a car that doesn't have a bypass port on the water pump. Do you know of any specifically?
 
57_BN4 said:
In 20 years of wrenching I have yet to see a car that doesn't have a bypass port on the water pump. Do you know of any specifically?
Click to expand...

I guess I was responding to what someone else said.
So do they all have a different design? - where are all the sleeved thermostats? Just asking...
 
steveg said:
where are all the sleeved thermostats?
Click to expand...

Rare to find a sleeved thermostat as it wasn't a very good design.

The 'modern' wax thermostats don't bother to block off the bypass as the general consideration in the 60s-70s designs was probably that the bypass flow was not significant enough to matter. By the 80s the 3-way thermostat was reasonably common except the sleeve was replaced by a disc on the bottom of the wax capsule. As the thermostat opens near full, the disc is pressed over the bypass port which is directly below the thermostat.

Below is a bypass (3 way) thermostat shown upside down on the right. That style should be fairly easy to convert to a sleeve type by soldering on the sleeve part of a bellows one.
bypass_thermostat.jpg


Andy.
 
57_BN4 said:
Rare to find a sleeved thermostat as it wasn't a very good design.

The 'modern' wax thermostats don't bother to block off the bypass as the general consideration in the 60s-70s designs was probably that the bypass flow was not significant enough to matter. By the 80s the 3-way thermostat was reasonably common except the sleeve was replaced by a disc on the bottom of the wax capsule. As the thermostat opens near full, the disc is pressed over the bypass port which is directly below the thermostat.

Below is a bypass (3 way) thermostat shown upside down on the right. That style should be fairly easy to convert to a sleeve type by soldering on the sleeve part of a bellows one.
bypass_thermostat.jpg


Andy.
Click to expand...

Point taken.
 
I think I have made progress in stabilizing the engine temperature in my BN7 following suggestions made on this forum. To recapitulate, my car's temp gauge moved above 200F at sustained speeds around 65 mph in 80 degree weather. This car is running a six-bladed fan (I think) with fiberglass blades. When I checked to see what thermostat was installed and found none present, I pulled the radiator and took it to a shop. It was recored with a core the proprietor said would flow a great deal more coolant. Still running without a thermostat, I soon found the car creeping above 200 degrees in 80-plus weather. I confirmed that temperature with a hand-held temperature gun (infrared laser?). The header tank read 203 degrees. That was pretty disappointing, as I was expecting the radiator upgrade would bring a much lower temperature. I have now purchased and installed the Moss thermostat blanking sleeve, part number 434-135, $15.95. This is simply a short brass tube with three or four small (bleed) holes drilled in its circumference. The top is slightly swelled to engage the grooves in the head normally occupied by the rim of a thermostat. Moss said this device was designed for Healey race engines, and the objective is to blank off a port in the head that allows some coolant to recirculate back through the engine without going going through the radiator. That port is visible inside the head with the thermostat removed. I then fabricated a four-inch-wide fan shroud from sheet aluminum that runs around the sides and top of the radiator perimeter--I actually made this out of two pieces that overlap under the red-painted protective guard on the fan side of the radiator. I don't own a sheet metal break, so I clamped my work piece between two straight boards to put a 1/4" roll on both edges of the 4"-wide side pieces to give them more strength and to eliminate raw edges. This took part of the afternoon. Yesterday I took the car for a good run with the temperature just above 90 degrees. Eventually the temp gauge reached 190 degrees and stabilized there. I think that is a good working temperature, and I think those two "upgrades" may resolve my engine temperature issue. In retrospect, I wish I had tried running the car with just one of the "fixes" to get a feel for which was most significant. I'm in Florida and my fellow Healey owners commonly run their cars without thermostats and and with the heaters valved off. If I were up north, I would probably do what another forum members recommended, cutting the thermostat rim's seat in the head s bit deeper so that I could mount a normal thermostat atop the Moss-sourced blanking sleeve. The alternative, of course, is purchasing the very pricey original-type thermostats that have a sleeve sround the bottom of the thermostat. Happy to offer this to the seemingly endless discussion of Healey engine temperature issues.
 
If you replaced the rad, thermostat and fan and you are still running high then your problem may be in the engine??? Check timing? Points? Plugs? Back flushed the engine? Valve gaps?
I run 170 normally and 190 to 195 when very hot ambient temps with original 4 blade fan and re-cored to original rad. I hit 220 when climbing on very steep grades on 90+ days but quickly returned to acceptable. (I am at higher altitude but spend a lot at sea level).
 
RD -
This is good information. Followup good! Thank you for posting!

I've ordered a sleeve and plan on installing it with a thermostat on top by either adding a gasket or making a thicker gasket.
 
There have been several temperature-related threads recently, and as a result I've been doing some informal reading (that's code for "stuff I found on the internet using Google) on the subject. One of the things that always puzzled me was why running without a thermostat is bad, and in some cases can actually make an engine run hotter. I'll offer a few tidbits that seem to emerge in "reliable" sources.

First, running without a thermostat means it takes longer for your engine to come to operating temperature. This is bad for lots of reasons, but probably isn't much of an issue if you live in a warm climate.

Second, the reason some engines run hotter without a thermostat is that the thermostat produces backpressure on the water pump. Some water pumps will cavitate without this backpressure, which dramatically decreases water flow rate and leads to higher temps.

Just some fuel for the fire, so to speak...

Keith
 
I run a 160 thermostat in SoCal - therefore I assume it's open all the time once the car's warmed up.

TstatTop.jpg

The OD on the raised lip around the center opening is 1-1/4", the ID of the hoses. Therefore it looks to be about 15-20% occluded at full open. Assuming the valve opens far enough that the lip and crossbar are the flow-limiting factor.

Will followup when I get my bypass sleeve with t-stat installed.
 
I have a NOS AC 187-deg. (F) sleeved thermostat that I purchased from a vendor/Healeys e-mail list participant in The Netherlands several years ago. I can't say that it alone had much effect on the stabilized coolant temperature of the engine, which was always higher than I thought it should be - especially in summer. The operation of the sleeve is visible on the temp gauge, though, with the needle going up and down a bit as the sleeve rises and falls during warmup.
My beef with the available sleeved thermostats now is that they seem to be available only in the 160-deg. persuasion. I tried a 160 at one time, but it had no discernible effect on the running temp in summer, but it did make the car run too cold in winter.
Oh yeah, the only thing that finally fixed my overtemp condition for good was re-coring the rad with a modern, more-efficient core; but I still have the sleeved thermostat, too.
 
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