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v8 cooling 3.9 rover

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v8 cooling 3.9 rover
#1
  This topic is about my 1975 MG MGB GT V8 Conversion
Ricey30 Avatar
Ricey30 Phil R
Chessington, Surrey, UK   GBR
(25 posts)

Registered:
07/05/2017 02:19AM

Main British Car:
Mgb gt 1975 3.9 rover

v8 cooling 3.9 rover
Posted by: ricey
Date: August 26, 2018 06:49AM

Hi Guys

I have now sorted the build and nearly finished ready to post, but I am overheating just sitting still. its not even off the jack stands!

it is a 3.9 rover on a carb with performer manifold and later front timing cover so it has the higher mount range rover water pump. The plumbing is as follows:

the back of the inlet manifold goes direct to the right hand connection on the heater matrix

the left hand heater matrix comes back and plumbs to the right hand stub at the back of the water pump

the bypass from the thermostat housing at the front of the inlet manifold connects straight to the left hand stub at the back of the water pump.

the radiator is aluminium 2 core from supplier on ebay, dimensionally the same as a mgb v8 rad

it came with a 12 inch electric fan which I have mounted in front of the radiator against the slam panel. it is configured to push air into the engine bay

thermostat is 82 degree with 3 bypass holes drilled in for pre opening flow

i have a expansion tank with pressure cap which is on the inner wing about 2 inches below the top rad hose.

I am running RV8 headers through the inner wings

temp gauge is original smiths capillary attached to the inlet manifold.


so on start up it ticks over with timing circa 6 degrees btdc, it isnt tuned properly yet as cant run it long enough! Within 6 mins of starting the engine hits 90c degrees and thats with the fan running from the very start as I hard wired it to a switch temporarily. the temp will keep going up to over 95c before a bottle out and turn it off. this is with a ambient air temp of 70F and with the bonnet off.

I have pumped hoses to ensure airlocks out and I have an air tit on the top hose which I have bled and the expansion tank is 1/4 full when cold. ALL the hoses are hot with a slight dif between the top and bottom hose but not much. System is not pressured as in a blown head gasket as when running I can still compress hoses.

this is a new build engine and all components are brand new.

Have I got a cheap radiator that hasn't sufficient capacity?
Is the fan cheap and not powerful enough?
Do I need a second fan?

I understand these run hot but if the temp is at 90/95c with no bonnet, fan running, at idle, this cant be right?

any suggestions please

Phil

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mstemp Avatar
mstemp Silver Member Mike Stemp
Calgary, AB, Canada   CAN
If u can still compress the hoses, I would guess you have lots of air still in system, t stat not opening etc. They really can be that hard to bleed.

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Jim Stabe Avatar
San Diego, CA, USA   USA
Air in the system can be a problem but if you have bled it and are confident the air is out, I would look toward the fan. Pusher fans are never as good as pullers. 12" doesn't sound like enough, actually two 12" don't sound like enough. Do you have enough room to move the radiator forward and use a powerful puller like the 16" Ford Taurus or Volvo with a shroud that covers the entire core? The Volvo is especially nice because it has a built in mounting flange to attach it to the shroud. While you are at it you should ensure no air can get around the radiator into the engine compartment. This isn't an issue sitting still but it can cause the pressure behind the radiator to equal the pressure in front when moving preventing airflow through the core.



Jim

"If you want me to agree with you then we would both be wrong"

'66 MGB widened 11" with supercharged LT1 Chevy and 6 speed, C4 Corvette suspension
Pictures here Part 1 http://forum.britishv8.org/read.php?13,7581
Continued in Part 2 http://forum.britishv8.org/read.php?13,22422
Continued in Part 3 http://forum.britishv8.org/read.php?13,33108
Continued in Part 4 http://forum.britishv8.org/read.php?13,40751
Continued in Part 5 http://forum.britishv8.org/read.php?13,48698,48698#msg-48698
Continued in Part 6 http://forum.britishv8.org/read.php?13,61672

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mstemp Avatar
mstemp Silver Member Mike Stemp
Calgary, AB, Canada   CAN
At 70F ambient and only 6 min of running, doubt very much it’s fan, shrouding etc. Test the thermostat. Also, with the Rover V8 after filling radiators, it will take several cycles to get all the air out.

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ex-tyke Avatar
ex-tyke Graham Creswick
Chatham, ON, Canada   CAN
1976 MG MGB
Some new thermostats are toast from the get-go....I prefer to use a quality stat like Stant..
To eliminate that as a cause for your overheat issue, take the T'stat out and run a trial without.
The rad is probably capable but, as Jim states, low aiflow or insufficient recirc are usually the 2 major culprits for poor cooling performance.

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Ricey30 Avatar
Ricey30 Phil R
Chessington, Surrey, UK   GBR
Guys thanks fir that info, I’m going to see if I can get anymore air out and I’ll check thermostat in boiling water, as you say it’s pretty shocking that it heats up so quick

Due to the longer nose of the water pump the fan has to go in front of the rad between the slam panel. So in this position is it better to reverse it so it pulls air from the engine bay out to the front of the car rather than pushing cool air into the engine bay ?

I can fit a 14” on there with curved blades that moves 1500cfm, would that be worth considering as the 12” has the flat blades and I have no idea what the cfm rating is.

So is there an art to getting it to purge like leaving the top off the expansion tank?

Thanks

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Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
Phil I have a similar system with a 3,9 but for 2 by 10" pusher fans. It does warm up quick but never a problem on the road. It may pay to post a pic of your radiator connections. With pressure your still no wear near boiling. Mine gets to about 90*C quick, then stays there, never looks like boiling even in 45*C

Denis



68 B roadster, Daffodil yellow, supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine "3.9L Rover" early in 2016 with high comp pistons and a few other nice bits, plus a T5 ford trans. Started on the body late 2016 and complete late 2017, Did all the work myself, mechanical, body. paint etc.
Finished and going well, great to drive and quick. Now has a nice 3.23 LSD.

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Ricey30 Avatar
Ricey30 Phil R
Chessington, Surrey, UK   GBR
I’ll post a pic tomorrow ofvtge Hoses etc for clarity and approval as well as checking thermostat

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ex-tyke Avatar
ex-tyke Graham Creswick
Chatham, ON, Canada   CAN
1976 MG MGB
Quote: ...is it better to reverse it so it pulls air from the engine bay out to the front of the car rather than pushing cool air into the engine bay ?
Absolutely NOT!

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Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
I have found that with the RV8 style headers through the inner guards there is very little under bonnet heat. My stainless manifolds have stayed shiny with just a hint if bronze. I missed that bit about reversing the fan. That would be a backwards step. Denis



68 B roadster, Daffodil yellow, supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine "3.9L Rover" early in 2016 with high comp pistons and a few other nice bits, plus a T5 ford trans. Started on the body late 2016 and complete late 2017, Did all the work myself, mechanical, body. paint etc.
Finished and going well, great to drive and quick. Now has a nice 3.23 LSD.

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Ricey30 Avatar
Ricey30 Phil R
Chessington, Surrey, UK   GBR
Right that’s the pics of what’s in. Please note is a work in progress and multiple tiding jobs (alternator cradle) still to do!!!

I’m checking thermostat now


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Ricey30 Avatar
Ricey30 Phil R
Chessington, Surrey, UK   GBR
Well that explains it!

1. It’s got 88 stamped on it, I thought it was 82
2. That’s a boiled kettle and whilst it moved under finger pressure it doesn’t when hot

So hopefully prob solved. I will check New stat before fitting.

Any of you guys with the higher 3.9 pump can confirm the pipe work at the back for the bypass hoses is right that would be great

I’ll post once it’s back together

Thanks
Phil


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Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
Phil that looks OK you even have the same header tank and breather inlet as mine. I found using the center port in the edlebrock carb for the engine breather worked well with a 1/8" restrictor to get a good engine tune and tick over. Otherwise it got too much air. No fumes or oil leaks. I have the lower mounted water pump. That fan should easily do the job, it would be close to the two of mine and it never looks like overheating.

Denis



68 B roadster, Daffodil yellow, supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine "3.9L Rover" early in 2016 with high comp pistons and a few other nice bits, plus a T5 ford trans. Started on the body late 2016 and complete late 2017, Did all the work myself, mechanical, body. paint etc.
Finished and going well, great to drive and quick. Now has a nice 3.23 LSD.


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Ricey30 Avatar
Ricey30 Phil R
Chessington, Surrey, UK   GBR
Denis nice tip about the breather

Mine as you see us open to catch tank and it smiokes gently of wispy fumes, and the tick over is all over the place as if there is an air leak.

I’ll try your rebreathe idea with the restrictor and see what happens

Cheers

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Ricey30 Avatar
Ricey30 Phil R
Chessington, Surrey, UK   GBR
Right quick update I have progress!

1. first thing we noticed was I had the vac advance for the dizzy connected to the back of the diaphragm not the top. So we reversed this and blocked off the bottom nipple instead. the dif this made was enormous, in that the exhaust headers were no longer running so hot that they were melting the plastic shrouds on the shockers
2. re timed it and connected breather to front of the edolbrock in the middle as Denis suggested. Now ticks over nicely, albiet a bit lumpy but I do have a performance cam in there and it is currently at 6 BTDC with hose disconnected.
3. left the stat out for the time being
4. bled thoroughly

Had it running for over 10 mins with it sat at around 80/85, started creeping up to 90, so turned on the fan and it held it at 90 no problem. ONly issue this is with the bonnet off and stat missing.

With the bonnet on it hits 95 pretty quick with the fan going. However looking at Denis' fan set up he has twin 10" at a guess, and my 12" is not a known brand and i doubt its no where near as affective as a branded fan.

But without the bonnet it now sits at 90 with the fan on with no issues at all.

So, I was going to get two fans to fit at the front and see if that helps and would re fitting the stat help in slowing the water movement down to help cool it?

Your opinions please

a very pleased Phil

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