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Old 12-27-2014, 06:33 PM   #1
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Default inline electric coolant boost pump

Evening one and all, running a few ideas through my head re keeping a turbo charged mx5 1.8 turboed engine cool. There is a wealth off information on the coolant reroute to keep the flow through the block even and to avoid poor flow on cylinder 4 however I don't see anybody trying an in line electric "booster pump" installed on the heater line. This probably means it's not a good idea?.

I have an bosch electric coolant pump from a C class merc. The inlet and outlet are the same diameter as the heater hoses. I have no heater anyway, the engine is in a miata based kitcar.

There is a fairly substantial flow on the pump when I tested it in a bucket. This would certainly scavenge the coolant from the 4th cylinder, I understand the heater flows even with the thermostat closed ?. My concern is that it would then pressurise the system and may be even force coolant past the mechanical water pump. Does anybody have any experience of a similar setup or thoughts on such a setup?

Kind regards

Hec
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Old 12-27-2014, 11:36 PM   #2
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There is already adequate flow through the heater circuit either with or without a reroute.
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Old 12-28-2014, 12:18 AM   #3
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I'm thinking a reroute is a simpler solution. Plus, I'd be worried about cavitation in the rear cylinders.
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Old 12-28-2014, 02:59 AM   #4
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Simpler = Better . . . always.
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Old 12-28-2014, 02:46 PM   #5
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No you dont wan any extra flow through the heater circuit. If you were going to run an inline booster pump between the radiator and the water pump is the only approriate locaiton.
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Old 12-28-2014, 05:21 PM   #6
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Not a good idea
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Old 05-10-2015, 06:58 PM   #7
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Coolant pump idea now officially binned, thanks for the advice.

The coolant systems has me thinking though, I have read a lot about the reroute for the coolant to aid cooling on cylinder 4. A lot of people move the thermostat to the back of the engine and from there to the top radiator hose.
This in itself is a fairly simple concept to understand.

My question would be this though, the water pump is turning and therefore pumping when the engine is running. With the thermostat shut the water pump is still turning, I am assuming still " sucking" water from the lower radiator hose and into the waterpump then block. Where does this extra capacity into the block go until the thermostat opens. I know the heater hose and oil cooler have water fittings outwith the thermostat control, is it these that provide enough flow to prevent the water pump from stopping??
Or is there some kind of pressure based byass on the waterpump whilst the thermostat is shut?

I hope that makes sense,

Cheers
Hec
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Old 05-10-2015, 07:42 PM   #8
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It goes through the heater core, that's the reason the heater core returns to the water pump suction side. It does not draw from the radiator when the thermostat is closed.

It is important to keep this feature with a reroute.
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Old 05-10-2015, 07:53 PM   #9
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It goes through the heater core, that's the reason the heater core returns to the water pump suction side. It does not draw from the radiator when the thermostat is closed.

It is important to keep this feature with a reroute.
Thanks for the reply, this is kind of where my confusion is stemming from, the heater core return goes back to the same return as the bottom radiator hose, I believe its the mixing manifold . Am I correct in assuming if the thermostat is closed, the water cannot physically be pulled from radiator therefore the path of least resistance is to pull water from the heater core, providing a coolant loop in the block prior to the thermostat opening (which when open would then allow water to be " pulled" from the lower radiator hose into the mixing manifold.).

Cheers

Hec
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Old 05-10-2015, 08:14 PM   #10
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Yep, that's it. It keeps the block an even temperature and it allows the pump a place to flow during warmup.
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Old 05-10-2015, 08:39 PM   #11
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Quote:
Originally Posted by bighecmac View Post
Thanks for the reply, this is kind of where my confusion is stemming from, the heater core return goes back to the same return as the bottom radiator hose, I believe its the mixing manifold . Am I correct in assuming if the thermostat is closed, the water cannot physically be pulled from radiator therefore the path of least resistance is to pull water from the heater core, providing a coolant loop in the block prior to the thermostat opening (which when open would then allow water to be " pulled" from the lower radiator hose into the mixing manifold.).
When the thermostat is closed, the flow of water into the top of it is greatly restricted. Thus, the water pump will primarily draw water in from the heater return.

So when the thermostat is closed, the flow of water is from the pump into the front of the block, upward and rearward towards the outlet at the back, into the heater core, out of the heater core, into the mixing manifold at the front of the block, and back into the water pump.

When the thermostat opens, it provides a path of lesser resistance, thus, a large amount of coolant flows through it and into the radiator, bypassing the heater core. It's this phenomenon which creates problems when the thermostat is in the front. All of that water going out the thermostat isn't flowing though the majority of the block and head, which diminishes the ability of the cooling system to extract heat from the engine. Moving the thermostat to the back of the head forces all* of the coolant to flow all the way through the whole engine.

* = there are a very minor bypass to deliver water to the oil cooler and to the throttle body. The amount of water travelling through this path is relatively trivial and not of great concern to engine as a whole
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Old 05-10-2015, 08:47 PM   #12
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Yep, that's it. It keeps the block an even temperature and it allows the pump a place to flow during warmup.
Brilliant gents and thank you. Thats my head around that. Leads me nicely onto part two then. I have a housing That fits the rear of the cylinder head but only with the 32mm outlet for the radiator. Its a kitcar installl so no heater is necessary or desired. I have fed my turbo water from the port next to the oil feed on the exhaust side , its a 94 1.8 block.

Will this, coupled with the factory oil cooller / throttle body water feed, provide enough movement on terms of coolant in the "closed" loop to keep the system happy until the thermostat opens.?

Its an m12 banjo feeding coolant to turbo via 8mm hose

Alternatively a 2 or 3 mmm hole drilled through thermostat plate help to relieve the pressure . ??

Cheers , Hec
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Old 05-11-2015, 10:25 AM   #13
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Just throwing this out there. The water pump is a centrifugal type which by definition is not positive displacement. When the fluid being pumped has no where to go, the pump does not build pressure - the pump spins without actually doing any work on the medium.
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Old 05-11-2015, 10:57 AM   #14
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32mm may be enough for the radiator but you will need adequate flow through the engine to prevent localized hot spots and keep the temperature somewhat even across the engine. It will also require a reasonable volume of flow across the back side of the thermostat to allow it to respond well to fluctuating engine temperatures. You don't want the engine to get hot and the thermostat not have a good indication of that because there is little flow near it. A hole in the thermostat will help this.
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Old 05-12-2015, 10:43 AM   #15
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Thanks Gentlemen, I feel better informed and more confident that my rerouting plan is likely to be a worthwhile exercise.

In summary then my system would be as follows

1994 1.8 engine with TD04 WRX turbo


STAT removed from front housing and relocated to rear of the cylinder head inside the 1.6NA stat housing. This does away with hearer core connections altogether. The rear housing is plumbed to the top hose on the radiator running past exhaust manifold (well insulated). A 3mm hole bored in stat face to assist in flow whilst stat shut. The water feed to the oil cooler and TB remain in place and are still routed to front housing and onwards to the mixing manifold. THis again should assist with flow whilst the stat shut. The front housing has been drilled and tapped and the coolant temp sensor plumbed there for the megasquirt.

The turbo water feed is taken from the factory drilled hole in block / coolant channel below the exhaust manifold and next to the oil feed. (M12x1.5 for if it assists anybody in the future). From the turbo the water is returned to the mixing manifold via an 8mm coolant hose . (Mixing manifold has had a 3/8bsp bung welded in place, where the heater core returned previously, and then an 8mm hose tail screwed in).

I have no need for a heater in the kit car.

I hope the results of such a reroute would be a more evenly cooled engine/block which would also make tuning the engine easier and with more reliability.

Many thanks again,

Hec

Last edited by bighecmac; 05-12-2015 at 10:55 AM.
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