18 replies to this topic

[Tomfoolery]

I have a 93 Italian Job with a 1275 engine. I've taken off the water pump and as expected its at the end of its life. I was about to replace it and fit a new bypass hose but have seen some people getting rid of it. Can I do this on my engine and will there be any side effects?

 

If I can get the adaptor out of the cylinder head (which looks scary to try with the head in place in case it breaks) is this the part I need to seal it?

 

http://minispares.co...ting/Water.aspx

 

Thanks for the advice.

[dyshipfakta]

Just replace it for silicone you will never need to touch it again

[gazza82]

 

If I can get the adaptor out of the cylinder head (which looks scary to try with the head in place in case it breaks) is this the part I need to seal it?

 

 

It won't .. I had to destroy mine (it was snapped off anyway due to corrosion) and that was a pig of a job with it on the bench!!

[Tomfoolery]

Thanks. Safest option looks to be the long life hose.

[imack]

I'd stick with the bypass hose.
Unfortunately the blanking plug couldn't be removed from my head so I've had to resort to drilling a couple of 3mm holes in the thermostat to give some circulation with the stat closed, engine is very slow to warm up in colder conditions with the restricted but constant flow through the radiator caused by the holes in the thermostat.

[1984mini25]

The reason why the bypass hose is so wrongly accused of being so problematic and need removing, is because of the use of those horrid bellows type hoses. At the end of the day its a 2" section of inch a half inch diameter heater hose with 2 clips. Witch providing you don't fit the useless type mentioned, is no different than any of the other coolant hose on the car and no more likely to fail.

[Spider]

I've not had a by-pass on any of my cars going back over 30 years, not had any issues.

 

Apart from the potential for a leak, the location of them brings on cavitation and that's why they were done away with in the later cars.

 

It's removal also lets the Thermostat work as it should and get's the Heater working better.

Edited by Moke Spider, 13 November 2017 - 06:39 PM.

[nicklouse]

if you are not taking the head off i would fit a silicon version but get a water pump that has not been drilled for it. so you are taking the action of it away. or get a pump with take off and drill and tap and block it off.

[mikal]

I'm with Moke on this. Got rid of the bypass hose years ago, never had any overheating problems. That includes driving in 40 degrees C days in Australia and a year driving in Indonesia (Tropical, always hot and lots of traffic jams..)

(Modified 1293cc with Weber)

[ti666er]

"parts left out cost nothing and cause no problems". So why would a manufacturer install parts that were not needed?

[Spider]

"parts left out cost nothing and cause no problems". So why would a manufacturer install parts that were not needed?

 

That's a good question and in all fairness it needs to be followed up with the Question;- "Why was it later done away with?"

 

It was done at a time well before heaters were used on the A Series. With the take off on the head to the lower hose and then later, via a sandwich plate, there's well enough radiator 'by-pass' without adding to it. It was also felt that circulation was always needed, be it through the radiator or not. Having it does assist with filling the system too.

 

Also, these were designed at a time when coolants weren't in common use. This engine series was designed in the late 40 and first running in the early 50's.

 

Bear in mind, the By-pass doesn't By-pass the Thermostat, but the Radiator. Even when the Thermostat opens, a considerable flow of coolant flows via the By-pass and so goes un-cooled, continually dumping hot coolant directly in to the coolant inlet. Hardly conducive to trying to cool an warm or hot running engine.

[Pete649]

If abandoning the bypass hose do you need to do anything else apart from blanking off the ends where the hose would fit? Drilling holes in the thermostat for instance.

[Sprocket]

 

"parts left out cost nothing and cause no problems". So why would a manufacturer install parts that were not needed?

 

That's a good question and in all fairness it needs to be followed up with the Question;- "Why was it later done away with?"

 

It was done at a time well before heaters were used on the A Series. With the take off on the head to the lower hose and then later, via a sandwich plate, there's well enough radiator 'by-pass' without adding to it. It was also felt that circulation was always needed, be it through the radiator or not. Having it does assist with filling the system too.

 

Also, these were designed at a time when coolants weren't in common use. This engine series was designed in the late 40 and first running in the early 50's.

 

Bear in mind, the By-pass doesn't By-pass the Thermostat, but the Radiator. Even when the Thermostat opens, a considerable flow of coolant flows via the By-pass and so goes un-cooled, continually dumping hot coolant directly in to the coolant inlet. Hardly conducive to trying to cool an warm or hot running engine.

 

 

 

That's just it though, the bypass was never done away with on later cars, it was just done in a different way.

 

The 1992 onward 1275 carb engines retained the old type bypass hose between the cylinder head and the water pump. There was a sandwich plate under the thermostat housing which fed the heater circuit only, this did away with the heater take off on the cylinder head near cylinder 4. The bottom hose has one connection on it.

 

The 1992 onward SPi engines did away with the old style bypass hose. Again there was a sandwich plate under the thermostat housing which fed the heater circuit like the carb engine, but also fed the water jacket in the inlet manifold, which then returned to the bottom hose. The SPi bottom hose has has two connections on it. The coolant temp sensor is mounted in the bottom of the inlet manifold, so there must be a constant coolant flow, therefore, a bypass.

 

The 1996 onward MPi engines, much the same as the SPi engines fed the heater circuit from the sandwich plate, but on the MPi bottom hose, there is a direct connection from the heater circuit off the sandwich plate direct to the bottom hose. This is the 'T' section that can be seen on the bottom hose. There is a plastic restrictor in this connection into the bottom hose which is about 6 or 7mm in diameter. The bottom hose has three connections on it (the third for the expansion tank).

 

The purpose of the bypass is to allow some circulation of coolant across the thermostat wax element all the time. Without any sort of bypass, the coolant will stagnate, and the only way for hot coolant to reach the wax element of the thermostat is by convection, that is until the thermostat starts to open.

[Sprocket]

If abandoning the bypass hose do you need to do anything else apart from blanking off the ends where the hose would fit? Drilling holes in the thermostat for instance.

 

abandoning the bypass and drilling a hole in the side of the thermostat will work, but in very cold weather, the engine will struggle to achieve running temperature.

[Avtovaz]

you dont need to use silicone hoses although they are really good. you just need a good corrosion inhibitor in your rad [aka antifreeze]

 

>imho< flow around the stat with out a bypass hose wont be too much of an issue, its right by the pump.

Edited by Avtovaz, 21 December 2017 - 10:33 PM.