16 replies to this topic

[Petrol]

First of all, I know this has been done to death but I still can't find some definitive answers.
I've removed the bypass hose from my 998 road car and drilled some holes in the stat as suggested. This worked great in summer but now it's getting colder, it's taking too long to warm up which is not good. I'm planning on using the car right through winter so I need to sort it.
I understand the bypass hose is there to allow coolant to circulate around the block and head when the stat is shut. This circulation prevents hot spots during warm up and also allows heated water to reach the stat so it starts to open at the required temperature. I can't find any mention of what opening the heater valve does though. Am I right in thinking if I leave the heater valve open and fit a non drilled stat there will be sufficient circulation during warm up?

Thanks for looking and I would appreciate any comments

Pete
 

 

[nicklouse]

there was no need to drill holes the single hole with the wiggly thing is all that is needed as that allows air to pass when filling.

 

the extra holes are what is reducing the warn up time.

[Spider]

Holes or no holes, even when shut off, hot water will always rise to the top.

[imack]

I've experienced exactly the same symptoms as you have when drilling holes in the stat and I've only ever put one 3mm hole in it. I now run an undrilled stat and always run with the heater tap fully open to allow circulation - even in summer. Warm up is much quicker in autumn evening temperatures but I don't drive it in the winter so don't know about lower temps.
I'd never willing do away with the bypass hose again, never had a problem with it in the past 35 years.

[unburntfuelinthemorning]

Why was a bypass hose fitted if it wasn't needed?

[Deathrow]

I like to think of it as a circuit.

 

Heater valve closed, thermostat closed, with bypass.

This is the smallest circuit available, so you're heating the smallest amount of water.

water pump -> engine block -> cylinder head -> bypass hose -> water pump

Heater valve closed, thermostat open.

Normal operation, radiator provides cooling capacity.

water pump -> engine block -> cylinder head -> thermostat -> radiator -> water pump

The problem I see with removing the bypass and drilling the thermostat is that, while water can pass, it's now moving in to the radiator, which means the water being pushed in to the water pump (and subsequently the engine) is cold water. Additionally, it creates a high restriction in the waters path (the closed thermostat).

 

If you were to run with the heater valve open, I think you'd have improved warm up times just because of the smaller capacity of the heater matrix vs. the radiator. However, on the other side of the coin, the decreased flow offered by the closed thermostat might actually allow the water in the block to heat up faster, despite the water entering the loop being cold from the radiator.

I think you'd have to experiment. I don't suppose you have a thermal camera? It'd be very interesting to see the engine warm up from cold in the different configurations to see how heat spreads through the system.

[gazza82]

Why was a bypass hose fitted if it wasn't needed?

 

To drive us all nuts when it split!

[daenesh]

Why was a bypass hose fitted if it wasn't needed?

 

So the common man could go "Ahhh.. another nonsense fitted pipe I can remove!"

[Petrol]

I've run Minis for years and never had a problem with the hose. I always used proper heater hose not the concertina type but that said, hose quality is not what it was. It seems to me that the bypass hose removal mod hasn't been properly sorted but I fully understand why removing it has appeal.

With the bypass removed, the thermostat closed and heater valve shut off, the water pump is pumping a dead end. Not good!

Drilling holes in the thermostat doesn't work because water will pass through the radiator increasing warm up time. If it's cold the heater will need to be on making things worse.

Engine cold, stock setup, heater valve closed and stat shut.
The water pump pushes coolant into the block, it flows into the head and returns to the water pump via the bypass hose. The pump is flowing coolant through the block and head to prevent hot spots. This raises the question why is the bypass on the same side of the engine as the water pump? Coolant will take the easiest route meaning cylinders 3 & 4 will get hotter. The stat is on the same side too. Interesting.
With the heater valve open, it's a different situation. Coolant will flow across the block and into the head to cylinders 3 & 4 more easily reducing hot spots. Some of the coolant will of course return via the bypass hose.

The more I think about this bypass, the more I think there is a better way of plumbing the coolant system up. When it's cold you need the heater on, no bypass and no holes in the stat. This will give minimum hotspots in the block / head and maximum heat to the heater.

I'm going to fit a non drilled stat and run it with the heater valve open and see how it goes. My oil and water temp gauges are accurate because I calibrated them so it will be easy to see what happens. Don't forget that oil typically takes twice as long as the coolant to heat up. I'm sure there is a better way for a road car than drilling the stat. I have a few ideas but at the moment, I'm thinking of a bypass that goes from the heater valve take off point on the head, back to the pump. This will require a different type of heater shut off valve, a T piece and a restrictor. I'm surprised no one has got to the bottom of this bypass removal before.

Pete
 

 

[timmy850]

Perhaps a better way for the coolant to flow is through one of the dry deck kits. These blank off all the coolant passages between the head and block and force all the coolant through the block, then out the end, up into the head and then out the thermostat housing. Then you've got good flow all the way through the block and head

 

Kits like this use a special head gasket and don't require the ports to be blocked off

https://www.med-engi...ck-kit-complete

 

You can also buy 4 port heater taps. Theoretically if there was enough room you could turn on the bypass when cold and then turn it off or divert the coolant another way

[Petrol]

I don't think I can fit the dry deck due to lack of space. I'm running a pedal box servo but thanks for all the replies.
I've fitted a new stat and just cut off the wiggly thing. The heater valve is open, the car heats up in half the time and the heater works a treat now.
Great fix for winter but long term I'll fit a 4 way heater valve which is a simple mod and will be a proper solution.

 

Pete

[nicklouse]

the wiggly thing does not need to be removed. Try closing the heater tap. You will find everything still works as normal.

[croc7]

Pete mentioned that with no bypass, no holes drilled in the ‘stat that the pump would be pumping a dead end. My thinking on this is that, if so, you could end up with pump cavitation at best and at worst, blowing a hose. So am I correct in that there should be some sort of ‘pressure relief’ in the water circulation circuit, whether it be via a drilled‘stat, a bypass hose or open heater valve? Or OK with no bypass but with an undrilled ‘stat with the wiggly thingy?

Edited by croc7, 04 November 2019 - 02:40 AM.

[Spider]

Pete mentioned that with no bypass, no holes drilled in the ‘stat that the pump would be pumping a dead end. My thinking on this is that, if so, you could end up with pump cavitation at best and at worst, blowing a hose. So am I correct in that there should be some sort of ‘pressure relief’ in the water circulation circuit, whether it be via a drilled‘stat, a bypass hose or open heater valve? Or OK with no bypass but with an undrilled ‘stat with the wiggly thingy?

 

No.

 

The water Pump is a Centrifugal Pump design. The correct way to throttle or shut off flow from this type of Pump is in fact to 'valve' the Pump Outlet.

 

Look up 'using centrifugal pumps' and I'm sure you'll not only see the similarities between the pumps but also how they can be used.

 

A very long term client of mine is a Pump Designer and Manufacturer (among the world's biggest). Long time back, I had a chat and some follow up discussions with the Test Engineer (who I often worked with on special projects) about out pumps and the cooling system flow path in the A Series.

 

The very first item he asked about when looking at the Pump was the By-pass. He was highly critical of it as in his opinion, it would have bought the onset of cavitation on at a lower speed. He suggested if it was to be retained, to run the pump at a slower speed and increase the system pressure to around 24 PSI or higher, or do away with it. After his look at the cooling circuit flow path, the only value he could see in it was a slightly quicker warm up time, though, almost academically so, he also could see it aided with getting most of the air out on filling. The down side of running the pump slower though, was that the flow rate would be low along with low air flow (since the fan is also spinning on the same shaft). His opinion was that overall, there was next to no advantage in keeping it and that doing away with it would only be a plus in that for all practical purposes, cavitation would be a non-issue.

 

It's 'interesting' that Leyland it would also seem eventually cottoned on to the By-pass location an issue too, though, I don't know why but can have an educated guess.

 

My own findings over the last 35+ years is that I'm yet to find an issue by not running one. OK, yes, there is in fact one issue I have had without one, that is it takes a couple of 'bites' to fill the cooling system from dry, other than that, it's increased reliability and I'm sure also extended pump impeller life.

[KTS]

 I have a few ideas but at the moment, I'm thinking of a bypass that goes from the heater valve take off point on the head, back to the pump. This will require a different type of heater shut off valve, a T piece and a restrictor. I'm surprised no one has got to the bottom of this bypass removal before.

Pete
 

 

i've been looking into the same sort of thing as well, but it's a bit of a challenge to find a bypass valve that might be useful.  there seems to be plenty of 4 way bypass valves available and some of them cable operated, but not a great deal of choice if you only want a 3 way bypass

 

about the only thing that comes close is this one - might be possible to rig it up to work off a cable...

 

https://www.ebay.com...7-/281115826873

Edited by KTS, 04 November 2019 - 03:14 PM.