Just spoilt my weekend. Finally got 4.2 into Hawk and did the 30 mile cam/bearing run-in with one top up for water en route. However since then although she warms up as normal, temp goes to 100+ briefly back to low 80s then after another couple of minutes repeats this cycle with temp rising in about 10 -15 seconds staying there for a minute or two then dropping again. ad finitum. Browsed forum archives, replaced thermostat (twice, one 74 one 82) pressure cap(twice) with no difference.
Changed temp gauge (Smiths cappillory) for an elect. one - same readings, just slower response. No bubbles in header tank - no water loss (at least after I remembered to put temp sensor back in!)
Strangely whilast sitting in driveway for ten minutes while I did timing , check fan coming on - no problem
What next gentlemen?
ps notice I'm avoiding any mention of p***** block
Overheating cycle
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Wilts289
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- Joined: Sat Nov 24, 2007 12:10 am
- Location: Devizes, Witshire
Hi Marky,
yup stat right way round, filled and refilled many many times inc bleeding off heater hose, just been trying again and now it DOES the cycle when stationary. Also have bleed in top hose for air locks. Tried jacking up front as suggested. Oil temp sits at 75 when stationary, oil pressure normal. Only thing I've changed since old 3.5 was to drill Edelbrock manifold as suggested by another contributor, but cant see how that cause it, it fact thought it might help reduce airlock problem.
yup stat right way round, filled and refilled many many times inc bleeding off heater hose, just been trying again and now it DOES the cycle when stationary. Also have bleed in top hose for air locks. Tried jacking up front as suggested. Oil temp sits at 75 when stationary, oil pressure normal. Only thing I've changed since old 3.5 was to drill Edelbrock manifold as suggested by another contributor, but cant see how that cause it, it fact thought it might help reduce airlock problem.
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Wilts289
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- Joined: Sat Nov 24, 2007 12:10 am
- Location: Devizes, Witshire
Yes correct manifold outlet fitted with lower bypass pipe below. Manifold mod as follows.lifted from archives
"On the Edel setup, the water from the heads firstly hits the temp sender which only senses the right hand cylinder head temp and then flows to the chamber at the back of the manifold where the heater feed is. It then returns forward to the thermostat plenum chamber to act upon the thermostat. This means that the water is cooled by the charge air flowing thru the manifold before it reaches the thermostat so even though your engine is running hot, the thermostat 'thinks' its cool!! Whats more, the faster you go, the more air the engine takes in and the temperature differential will get bigger. I wired my cooling system up with 7 'K'type thermocouples and a calibrated digital thermometer to find all this out and measured up to 15'C differential between the cylinder head exit temp and the thermostat! I contacted Edelbrock but got no reply. To get around this problem I drilled 2 x 13mm ports internally to allow water from the cylinder head exit ports to allow flow directly to the thermostat plenum chamber and that brought the temperature differential down from 15'C to 2'C, (if you look at an Offy manifold you will see these holes as standard). This also helps with airlocks. as high as possible under the bonnet. "
Made sense to me so I did this before installing it in the 4.2!
What surprises me is how quickly temp goes up and down - 5 seconds from 85 to 105 and only a frew seconds more when it cools down, its as if someone is turning a cold tap on and off!
"On the Edel setup, the water from the heads firstly hits the temp sender which only senses the right hand cylinder head temp and then flows to the chamber at the back of the manifold where the heater feed is. It then returns forward to the thermostat plenum chamber to act upon the thermostat. This means that the water is cooled by the charge air flowing thru the manifold before it reaches the thermostat so even though your engine is running hot, the thermostat 'thinks' its cool!! Whats more, the faster you go, the more air the engine takes in and the temperature differential will get bigger. I wired my cooling system up with 7 'K'type thermocouples and a calibrated digital thermometer to find all this out and measured up to 15'C differential between the cylinder head exit temp and the thermostat! I contacted Edelbrock but got no reply. To get around this problem I drilled 2 x 13mm ports internally to allow water from the cylinder head exit ports to allow flow directly to the thermostat plenum chamber and that brought the temperature differential down from 15'C to 2'C, (if you look at an Offy manifold you will see these holes as standard). This also helps with airlocks. as high as possible under the bonnet. "
Made sense to me so I did this before installing it in the 4.2!
What surprises me is how quickly temp goes up and down - 5 seconds from 85 to 105 and only a frew seconds more when it cools down, its as if someone is turning a cold tap on and off!
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Ian Anderson
- Forum Contributor
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- Joined: Sun Nov 19, 2006 9:46 pm
- Location: Edinburgh
Take the thermostat out completely
And see if that eases the problem.
If so you could have a problem with not enough flow through the stat when closed / cold. This happens in GT40s and they drill a number of 1/4 inch holes around the thermostat edge to let water flow more easily and it tends to stabilise the crazy fluctuations.
Ian
And see if that eases the problem.
If so you could have a problem with not enough flow through the stat when closed / cold. This happens in GT40s and they drill a number of 1/4 inch holes around the thermostat edge to let water flow more easily and it tends to stabilise the crazy fluctuations.
Ian
Owner of an "On the Road" GT40 Replica by DAX powered by 3.9Hotwre Efi, worked over by DJ Motors. EFi Working but still does some kangaroo at low revs (Damn the speed limits) In to paint shop 18/03/08.
I have also done the drilling mod to my edelbrock manifold, I did not have a issue before the mod but a mate of mine had a big problem with the temp suddenly shooting up to 110 degrees for no apparent reason.
We both have 74 degree stats fitted and I think that that's a big help. (I have drilled 3 holes in my stat as well).
I run a 4.6 lump with an sierra 2.3 diesel rad and the temp sits between 75-80. (my mate runs a 3.5)
Like others have said, I'd run it without a stat just to prove that the coolant system is working with no restriction.
It's not something daft like the water pump impeller loose on the shaft?
Pete
We both have 74 degree stats fitted and I think that that's a big help. (I have drilled 3 holes in my stat as well).
I run a 4.6 lump with an sierra 2.3 diesel rad and the temp sits between 75-80. (my mate runs a 3.5)
Like others have said, I'd run it without a stat just to prove that the coolant system is working with no restriction.
It's not something daft like the water pump impeller loose on the shaft?
Pete
Similar prob to one I had. I drilled a 6mm hole in the stat flange and fit it with the hole at the top so it gets air out asap. Then fitted an 82 degree stat with my leccy fan switch set to 90 C.
Solved the problem on my 3500 and the same setup ids fine with the 4.6 now.
Edelbrock performer 360 manifold originally and now a 3.51 mani.
Solved the problem on my 3500 and the same setup ids fine with the 4.6 now.
Edelbrock performer 360 manifold originally and now a 3.51 mani.
Perry Stephenson
MGB GT + Rover V8
9.62 @ 137.37mph
Now looking for 8 seconds with a SBC engine
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Wilts289
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- Joined: Sat Nov 24, 2007 12:10 am
- Location: Devizes, Witshire
Good Evening Gentlemen,
What can I say! Followed advice, bought 74 degree stat on way home, tried drilling 1 hole first and off I went. It did its up/down cylce twice and then settled. Drilled 3 more holes and now its running PERFECTLY. What a knowledgable crew you are and I thank you with a big grin on my face!!!!! Just need a couple of 100 more miles on her and then we'll see what the second set of carb barrels do!!!
What can I say! Followed advice, bought 74 degree stat on way home, tried drilling 1 hole first and off I went. It did its up/down cylce twice and then settled. Drilled 3 more holes and now its running PERFECTLY. What a knowledgable crew you are and I thank you with a big grin on my face!!!!! Just need a couple of 100 more miles on her and then we'll see what the second set of carb barrels do!!!
