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 Posted: May 24, 2015 11:35AM
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CA

HOT / Diddi's commnet about coolant taking the easy route and the possible overheating at cyl 4 and failure between cyls 3 and 4 reminded me of teh old Chrysler flathead 6's (1930's to 1950's). With the water pump up front on the engine and a long block, it needed an internal manifold to distribue coolant evenly along the block. When this manifold rusted out, the engine would boil in the back end.

.

"Hang on a minute lads....I've got a great idea."

 Posted: May 23, 2015 09:20AM
 Edited:  May 23, 2015 09:26AM
mur
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One of the most important parts of the cooling system is the expansion tank. Most 1300 engine equipped cars in the other parts of the world came with one. I like Volvo items far more than the BMC tanks. Here is one in a catalogue. They are fitted by a nice bracket that they clip out of, so hit the wrecking yards looking for this exact bottle!

//www.skandix.de/en/spare-parts/cooling-system/expansion-tank-engine-coolant/expansion-tank-coolant/1010844/

keep in mind an expansion tank is not an overflow bottle, it is part of the pressurized coolant system. A blanking cap style cap goes on the mini radiator and the pressure cap goes on the expansion tank.

//www.minimania.com/part/GRC126/Cap-Radiator-Non-Pressure-Blanking

 Posted: May 23, 2015 08:59AM
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CA
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Nodding...so like MUR I use a good 195 deg. thermostat common to V8 engines...but then I wander off based on my own long distance roamings in Minis with full loads where a wide range of ambient temperatures might be experienced and add both an auxilary radiator and the extra coolant volume that entails.  Simple, cheap has never let me down, easy to block off (same for oil cooler) in not so hot weather...and the aux. rad got Diddy Dave home from MMW in Arizona with both cracked head (between valve seats in #4 and in block between #3 & #4.  Sure we recrossed the Mojave desert leaving well before dawn to avoid the sun....

At Mid-Ohio last June, Dryk Bolger was having trouble with his ex-Miglia Mini apparently overheating...MUR ever the observant soul, though I might have the aux. rad in ROO the Aussie Van, so ROO loaned the aux. rad to Dryk's race Mini.  Finished the Can-Am Mini Challenge race...but ROO didn't get to keep the pretty silicon hoses!

 Posted: May 23, 2015 05:15AM
HOT
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At first something regarding the cooling issue of the thread starter.

A radiator will never cause an engine to run too cool. No matter how big it is. It´s allways the thermostat which allows  the amount of cool water to flow through the engine. If the radiator has more cooling capacity than needed, the thermostat will open less to controll the temperature.

So this is the area to check, if the engine is definitely running to cool. This has to be verified first, as also gauges can read wrong!!!

Regarding the bypass hose/system:

Dan is absolutely right regarding the above diagram. The arrow in hose #4 ist wrong. No matter if the thermostat or heater valve is closed or open, ther´s allways a constant flow through the engine to eliminate hot spots.

However, the above diagram shows the MPi with front mounted radiator , which was actually a step back regarding the bypass system as it is actually the "old" system with the hose between head and pump , only with a slightly relocated position.

The best bypass system was introduced with the `90s 1275 carburettor coopers and SPis.

To explain why: Water ist basically a "lazy" medium, which allways takes the way of the least resistance and likes to take "short cuts". The water flows from the pump into the block, then upwards into the head and out through the thermostat housing to the radiator and back to the pump.

When the thermostat is closed, there will be no flow through the radiator. But still, the water has to circulate somehow through the engine to eliminate hot spots.

This is realized by the bypass system:

On early 1275 engines and all small block engines via the bypass hose between head and pump. This "early" system has a downside!

There are several passages from the block, upwards into the head. 3ea larger ones between the cylinder bores at the manifold side and 8ea smaller bores at the "spark plug side".

As water is "lazy", most of the water will take the shortest way from the block upwards into the head. So the most upward flow is at the front (cylinder 1-2) and the least at the rear end (cylinder 3-4).

This leads to hotter running cylinders 3-4 with #4 being the hottest.

Just think about, where the most cylinder head gasket failures are experienced. Yes, between #3 and #4!

With the 1275 A+ Mini engines, Rover improved things dramatically as they invented a completely different "bypass" system. They connected the former heater valve port of the head (at the rear/hottest end) via a hose to the intake manifold and from there to the lower radiator hose. So, even with a closed thermostat, there´s allways flow from the pump, into the block, upwards into the head and out of the head at the far (hottest) end of the head. Even with the thermostat fully open, there´s still flow this way, as the pump also applies a suction to the lower radiator hose and in turn also to the rear end of the head.

The same system was used on the SPi engines.

On these engines, the sandwich plate underneath the thermostat only acts as a hot water takeoff for the heater. The heater return is connected to the heater valve and from there back to the lower radiator hose. The valve is in the "return" hose of the heater system!

The MPi basically went back to the system as it was used earlier on the Metros, with the front mounted radiator and no heater takeoff port at the rear end of the head...   ...a step back in time and development...   ...at least regarding the bypass system. And guess what? More head gasket failures between #3 and #4...Undecided

 

Cheers, Diddi 

 

 Posted: May 22, 2015 01:39PM
 Edited:  May 24, 2015 11:24AM
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CA

That item "4" in the diagram just looks weird -as if the directional arrow is wrong.  Both this and the heater return connect to the bottom rad hose, which the pump is drawing from. If item "3" is the heater control valve, and it was closed then the pump would draw down on item "4", providing a heater by-pass. even with the valve open, there is less resistance in "4" than going all the way through the heater (unless 4 is small diameter) so would short-circuit the heater. Even if flow in "4" is up. it would dilute heat available in the cabin.

(fixed stupic typos)

.

"Hang on a minute lads....I've got a great idea."

 Posted: May 22, 2015 12:20PM
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US

I believe the bypass is present on most Minis just in a different form.

Many later versions use a thermostat sandwich plate to provide this function.

Even the MPi with its unusual configuration has a bypass of sorts.

Sort of going off track, but it is important to verify the actual temp. I thought we had an overheating engine on a trip awhile back, but the gauge was off.

Terry

 Posted: May 22, 2015 11:47AM
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CA

Good point about the by-pass flow being from the head down into the pump. To the casual observer it may not be apparent.

The theory about drilled holes (I know it isn't necessarily yours, Mur) helping the thermostat may not be so well founded: Most heat is generated in a cylinder at the head. The coolant absorbs what it can, and with normal flow transfers heat to the rad for dissipation. Funny thing about the thermostat: the wax chamber which regulates it is supposed to be down into the head in a Mini engine. Unless there is an air pocket around it, the wax will be heated at the same rate as the coolant in the head. Hypothetically poking holes in the thermostat is supposed to permit circulation, which would only delay warming of the engine.

With a heater fitted (or at least a hose bypasssing a heater but providing the same circuit) the pump has something to draw on to generate a bit of circualtion in the engine to prevent hot-spots. Having the heater output hose conenctd to the head ensures that the collant pushed by the pump will flow up through the many cooling passages to the head, providing even distribution.

It would be itneresting to know why the by-pass hose was included and then omitted. I suspect that since early cars may not have had heaters, circulation was a problem. When we consider that the A-series engine was reputedly derived from a tractor engine, and no tractors of teh time had heaters, the by-pass may have been carried through from that earler design. Later cars got heaters, especially when it came to A+ cars of all sorts, so pehaps it was discovered that the bypass was redundant. Saving 4 parts ( hose, nipple and 2 clamps) and two drillings plus machining and labour would add up to sizeable economy.

Maybe.

.

"Hang on a minute lads....I've got a great idea."

 Posted: May 22, 2015 10:05AM
mur
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Water is pumped into the block by the water pump. It goes through the block, up into the head, and out the head either by the bypass, the thermostat or the heater take off. If it goes out the bypass, it is not cooled and it is pumped directly back into the block. If it goes out the heater take off, hopefully it is cooled, and it returns to the lower rad hose, and then the water pump. If it goes out the thermostat, it is cooled and returns via the lower rad hose and then the water pump.

If there is no by pass and no heater take off, the thermostat, if it is completely closed off, will be slightly slower to respond to the increase in temperature. However, this is in a fluid, a known coolant, it is mere inches from the heat sources, and I don't consider it a problem. Again, slightly slower. The drilled holes are there to make the thermostat more responsive by increasing flow past it when closed. There was some discussion of these holes being of help should the thermostat fail in a closed position. 

I am neither quoting nor arguing Keith's article. Again, I prefer a car with a proper functioning heater in any weather, and I drive in a huge temperature range, from -40°C to +40°C.

on my own race car, coolant flows from the heater take off to the upper tank of the rad At all times, but a proper thermostat is used and I don't have a by pass.

 Posted: May 22, 2015 08:54AM
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Interesting thread as I was going to post about bypass/no bypass at some point.

I will be running an MPi block in a Mk I body and it has no bypass. I have reread Calver's article on the hole drilling and still do not fully understand. I am trying to visualize the flow and I know that maybe the water passages in an MPi block have been modified, certainly the oilways have.

I have an A+ in a Mk I body now with no bypass and I have not noticed any issues. It does stay on the cooler side, but it does not get on the freeway or long trips too often.

Terry

 Posted: May 22, 2015 08:25AM
mur
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For a while there were thermostats with some sort of lock that would hold them open permanently if the engine overheated. Total gimmick. That is all I am referring to. Otherwise, when the wax leaks out of a thermostat they spring open. As for the hole drilling, I only suggested that the article be read and considered. If I had a non bypass A+ I would still use a proper thermostat, however I would never have a mini without a complete functioning heater system. I have used the defrost in LA and Atlanta, just as I would in any other car or truck.

 Posted: May 22, 2015 07:42AM
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CA

(Hunter2 is a man of few words today)

I have an 1275 engine with no bypass and tried Calver's hole suggsetion. Howeveer, I found that even with a good 195 deg, T'stat modified with the holes, my engine would not warm up properly in cool weather. I swapped it out for a new one with no holes and am very satisfied. It stays closed until the coolant in the head reaches the opening temperature. I get decent heat from the heater, and much improved driveability. I am not worried about the head overheating as to get anywhere close to hot enough for damage it would have to boil the coolant and the T'stat opens long before that. Contrary to one comment Mur made, I would recomment a "fail-open" thermostat - I think most common ones are made that way anyway. The reason is that if it does fail (the temperature sensitive part failing to operate) you want the thermostat to be open so that the engine does not overheat. The symptoms of this would be insufficient heat at the heater, engine runing poorly because it fails to reach optimum popeating temperature, and a top rad hose that warms gradually asns the engine warms. 

What should happen is that when you start your cold engine, the head gradually warms up, the T'stat housing heats more slowly (you can still touch it when the head below it becomes un comfortably hot) and the tpo rad hose stays cool. When the t'stat does open, its housing heats quicly, as does the top rad hose, and you may see flow in the neck of the rad. While this is happening, asuming your heater valve is open, the water pump will pull coolant from the head, through the heater (and through your alloy manifold if you bothered to plumb it in), and back to the block, providing some flow through the block and head. If during your drive, the rad gets too cool and the engine temperature begins to drop, the thermostat should close to sustain the engine temperature. No need for cardboard in the rad on cold days. Note, on really cold days the cardboard in the rad trick serves to keep the engine bay slightly warmer by restricting air flow from it.  Of course driving a Mini in realy cold weather is a bit insane - engine temp is the least of your problems. (Been there and done that down to -20 F or more, and yes maybe I was crazy.)

.

"Hang on a minute lads....I've got a great idea."

 Posted: May 22, 2015 07:40AM
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It's not good as the engine needs to be at operating temps for a variety of reasons. That being said, it should at a minium run the same temp as your t-stat. I'd replace it with a new one. It may be stuck open, removed, or has holes drilled in it. And as stated you should verify with a thermometer as a start.

 Posted: May 22, 2015 06:57AM
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 Posted: May 21, 2015 02:46PM
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Running too cool is bad because the engine never gets hot enough to burn the moisture out of the oil, which is really bad on a mini since most are subjected to short trips anyway.

 Posted: May 21, 2015 12:58PM
mur
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Always verify an issue. Use a thermometer that you have checked the calibration on and confirm you are running as cool as you think. After doing that, then fit a proper thermostat. I use 195°F units from a quality manufacturer. Minis take the same item as a small block chev. Do not fall for any gimmicks like larger valves, fail safe lock open items, floaty bleeder valves, etc. Some may suggest you use a lower opening temp thermostat but they don't get any more open in hot weather when the car does warm up and I have never embraced the various weak explanations for these.

If you have an A+ block without the bypass hose, and if you have no heater, then consider reading Calver's thoughts on thermostats and bypass holes in the articles section.

With a properly tuned 1275 on a warm day you should be able to see the temperature rise and fall as the thermostat opens and closes while you are driving at a steady speed.

 Posted: May 21, 2015 12:11PM
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US
Block some of the radiator and get the temps up and see if it affects it?

 Posted: May 21, 2015 12:11PM
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Sounds like you need to install or replace the thermostat.  Running too cool is a nice problem to have with a mini...

 Posted: May 21, 2015 12:02PM
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I had a four core radiator installed in my 63 and now I can't get the temperature past 140.  I was told that the only effect it will have is less gas mileage.  I have a 1275 engine and is getting about 25 miles a gallon.  Is that about average?