The Temperature Conundrum

[V8 Freak]

The scenario:

I popped a nice 4.6 V8 into the Defender a while back. (Thanks to Pod for letting it go..) The engine is V8 Development block with top hat liners and otherwise standard bottom end. Oversized valves, double sprung, and nicely ported heads. Tubular exhaust headers, Jan-speed exhaust all the way back. All controlled by an Omex 710 ECU.

It's a serpentine front end so the pump doesn't drive water round the heater system. The heater feed is from above #2 cylinder just like the RR 4.6 heater and feeds back into the bottom hose. I did this because I expected it to be lower pressure/in the draw of the water pump here and hoped this would promote enough flow around the heater matrix to offer adequate heat in the colder months.

New water pipes everywhere, radiator flushed through, no rotten fins, no blockages between fins... New Water pump, new 88 degree thermostat. (Initially)

I have a calibrated VDO gauge and sender. The sender is fitted in the inlet manifold over #1 cylinder. Originally the ECU temperature sender was here too. This was also calibrated through the engine management software.

I'm quite confident I know what the water temperature is at the top of the water cavity within the inlet manifold.

(The ECU temperture sender now located under the thermostat, where the water feed for the heater on a 3.9 V belt engine is normally.)

I've been through 8 thermostats now of varying temperatures. (82, 88 and now 74 degrees)

Some opened ok then didn't appear to close and the engine ran cold. Some opened on time but then seemingly didn't open enough and the temperature gradually increased. Some opened late and then closed early meaning a hot engine all round.. (Not good)

Those that seem to act near normal all showed the same symptons.

(All stats have the bleed holes at the top and are fitted with the temperature sensitive side inside the inlet water chamber as expected !)

The engine when ticking over gets warm as expected, fans cut in around 95 on the guage and the engine cools back into the 80's no bother. (Fans controlled by X-Eng switch fitted in the thermostat housing.... No room in the bottom hose and they do come on reliably at 95.)

I believe I have suitable ability to cool the engine as demonstrated by the fans and the drops in temperature when the stat opens under normal driving conditions.

When pottering around town or slow country lanes the temperature rises to around 100 degrees, then plummits into the 80's and repeats this process slowly. Even the 74 degree stat is doing this.

I cannot understand why the stats are not opening earlier when the two temperature senders are clearly registering a rise in temperature.

When on higher speed run, say 70 in overdrive or just 5th, the temperature spikes once and then settles down in the high 80's as expected. When I slow down and the stat closes as temperature drops, I have to go through the temperature spike again before it settles down.

To get round all of this up to now I have drilled two 4mm holes at the top of one of the "good" stats which allows a generous flow of water all of the time and seems to erradicate the peaks. It generally means the engine runs slightly cooler than desired, but cooler is better then too hot in my books!

The only other downside of this is that less water seems to head round the heater system this way. When peaking and troughing, the heater is definitely warmer.

That's about as much as I can tell you at present.. Please ask more questions and offer suggestions of things to try. I want this engine to last and don't want to cook it !

Please only sensible suggestions and none of the usual banter in terms of a nice diseasel wouldn't have any temperature problems etc.

Could I be running lean? (Although no pinking I can notice and runs real sweet...)

If timing retarded, would this cause excessive hot running?

Would posting timing / fuel injection maps help ?

Thanks in advance and sorry for the ramble.... Wanted to make sure I shared as much as possible to get the best responses.

Neil

[steve_d]

Have you got the correct pressure cap fitted and is it holding pressure?

Is the header tank higher than other parts of the cooling system?

Steve

[V8 Freak]

Yes Steve.

New rad cap, pressure holding but not excessive pressure in pipes. No water loss, no film in the oil and no funny smelling water, so not suspecting head gasket problems at present....

Expansion tank in normal place on O/S inner wing as per original 3.5.

Neil

[Hybrid_From_Hell]

Yep

Engine should have a target temp band of around 82 98 degrees, colder than 82 risks being too cold, higher than 98 pushes headgaskets etc

Pressure cap is one thing to look for

others are (in no order)

• Your mix of antifreeze to water ratio ?
  
• Viscous fan - the variable fan unit without one you can fight to keep temp right area
  
• Cowling - directs cooling onto engine as opposed to missing it
  
• Radiator whats it from ?
  
• System Bleed ? - air pockets wreak havoc
  
• You can change Water pump pulley for faster one, whats the OD of it now ? - there are options
  

Nige

[V8 Freak]

• Your mix of antifreeze to water ratio ?
  Was 50% but now lower. Just topped up with water this time through so probably under 30% Anti-freeze at present.
  
• Viscous fan - the variable fan unit without one you can fight to keep temp right area
  
• Cowling - directs cooling onto engine as opposed to missing it
  As discussed last weekend, this will probably get an outing in June when I've got the front apart anyways.... Even with fans running permanently the temperature spikes.
  
• Radiator whats it from ?
  No idea, was in there cooling the 3.5 when I bought it. It kept 3.5 and 3.9 under control and can cool the 4.6 when allowed to by the stats....
  
• System Bleed ? - air pockets wreak havoc
  Had heater hoses off and de-icer hoses for plenum off. Both gushing water ok and both take feed from the top of the chamber. Fairly confident no air pocket in the inlet manifold but will add back in the raised filler from the old 3.9 sometime soon to be double then triple check and be fairly sure air is out...
  
• You can change Water pump pulley for faster one, whats the OD of it now ? - there are options
  Pulley is standard one for the Serp front end and makes the belt fit ! (I'll measure and post up soon.)
  

[Hybrid_From_Hell]

Hmmmm

Post a pic of the rad showing side tanks and in and out

The viscous is a hugely usefull bit of kit, however the cowling adds more to the system than you can imgaine.

the cowling stops in efffect cold air finding the fastest way out of the area, ie exit down, left right etc anywhere but the engine. what in effect happens without a cowling is the fans capacity is reduced hugely, and just maybe reduces the core temp of the rad a bit - the cowling directs and forces air over the hot engine, without this the temp can be a piggy to control (ask me how I know ).

On the hybris I had a cowling but also blocked off routes each side of the rad so ANY forward entering air had to go through the cowling, the changes were frankly unbelivable

take your 2x elecrics off,........ fit a viscous and a cowling and then judge for yourself , for more do as I have and then add 2x fans as pushers on the front the the rad . the 4.6s have a small water jacket and respond to heat increses and decreases faster than 3.5 3.9 etc - you need to keep "On Top" of heat up and downs, without the cowling you'll struggle IMHO the rad size may also be a tad under whats needed - compounding the prob

Nige

[V8 Freak]

Been thinking about your responses Nige. (yes.. It did hurt doing all that thinking..)

I agree the viscous and cowling and bigger radiator etc. will all aid cooling, and I'll be replicating some of your cooling setup in June, but my concern is that for some reason I cannot fathom yet, the hot water is all collecting behind the stat and not getting to the radiator for cooling. So it doesn't really matter how much cooling capacity I have unless I can get the water there !!!!

Is there any reason anyone can think of why the stat isn't opening at the right temp on each occasion..

Could it be that flow is directed away around the heating matrix or plenum de-icer (Very small tube) and not enough washing around the back of the stat ?

I cannot understand how the temp sensors can pick it all up and the stat doesn't appear to react when I have one sensor below the stat and one just above it! Could it just be the sensors are so much quicker at reacting and just because I can see them reacting each second I shouldn't expect the stat to open within the same timescales....

Neil

[simonr]

Could it be that flow is directed away around the heating matrix or plenum de-icer (Very small tube) and not enough washing around the back of the stat ?

I cannot understand how the temp sensors can pick it all up and the stat doesn't appear to react when I have one sensor below the stat and one just above it! Could it just be the sensors are so much quicker at reacting and just because I can see them reacting each second I shouldn't expect the stat to open within the same timescales....

I wondered about both these. The sensor on my MegaSquirt used to spike all over the place - but the temp gauge was much more damped and showed an even temp. The thermostat is also very damped and cannot hope to adjust as quickly as engine running conditions change.

I guess it would be worth blocking off the heater & plenum just to see if there is an effect.

Si

[V8 Freak]

Good challenge Si...

I'll blank both off soon and see what changes....

[FridgeFreezer]

As you said, it seems to be a problem of water not getting past the stat rather than actual cooling ability. I had the same with a sticky stat (in fact two sticky stats, God bless Sh*tpart ) in the end I got fed up and just drilled a ~5mm bleed hole in the top of the stat and called it job done, it's been fine since.

Interesting re Simon's idea, I actually never bothered plumbing in the plenum heater (or indeed fitting it ) and don't have a heater plumbed in either. Header tank is on a nipple on the top of the rad as per RR.

If your fan(s) come on full gusto or nowt then I'd suggest wiring them as per BBC's twin-fan circuit that runs them at half speed then full speed, it's how mine works and it stops sharp cooling spikes, also you can hear when it's getting hot because the fans will kick into fast mode.

[V8 Freak]

It's a weird one Fridge...

When driving along with the big holes in the stat as you have done, I get no spikes and the fans never come on....

Even when I have the spikes, as soon as the stat opens and allows a flow, the fans have no need to come on as the water flows, is cooled and all is well in the world. The hot water doesn't remain over the switch for long enough to switch fans on... Once flowing it all works hunky dory.

[streaky]

Just as a comment.

I was running a 3.5 on carbs in the 130 before dropping a tweaked 4.6Efi in there. The temperature difference created by the 4.6 was huge. I was also running a top quality capilary temp guage.

The 3.5 had a standard rad, viscous fan and properly fitted shroud. Temperatures in the Middle east heat were acceptable. But when I put the 4.6 in the temperature guage was always reading upto the 95-100+ mark.

I was able to source an aluminium radiator which immediatly dropped the running temperatures back down to 85-90 under normal load. When the going got tough...the ali rad would really help bring the needle back down.

Decent quality silicone hoses that don't colapse under high revs and a good flowing radiator helps alot I found.

Regards.

S.

[tacr2man]

I would try the shut off heater/plenum circuit first , as suggested.

I would not change water pump speed as this can make it worse, due to cavitation.

I have had experience with big block ford in OZ that was a real pain with getting reliable cooling, fixed it by fitting inline thermo housing in bottom rad hose no thermo in top of block .

It sounds as if you have the cooling capacity in the rad, as the temp comes down pretty quick when ''triggered' , viscous with cowling is simple route. When driving above 50mph , fans dont really need to do much, due ram effect. The viscous is triggered by the hot air flow from rad , whereas lecky fans are working on water from block temp (usually) .

Do you run an oil cooler ? When you look at vehicle cooling system not a very good solution , engine gets hot , so you let the very hot water out the top of the block, and let very cool (comparatively speaking , esp depending on rad efficiency) into the bottom ? thermal shock ? JMHO

[V8 Freak]

Heater stuff will get done to see the difference regardless.

So I summise that the viscous may not help that much as the rad isn't getting hot until the stat opens.... Catch 22 ?

No oil cooler presently, although it is a consideration as I have a remote oild filter so easy enough to sort out.

Now where do I get me one of these inline stat housings ?

[Hybrid_From_Hell]

Neil.

Re our chat

You could also try removing themostat completely

DO FIT a plate known as a 'restrictor plate' in place of the thermostat.

I have seen these for sale........... can't remember where, but

The hole sizes tend to be 16mm minimum up to around 28mm on the bigger V8s (5.0+)

Bit of Ali and a file and a drill and a few mins should do it....

Maybe worth a try, .........I would start with a 22mm Hole

This plate then keeps the flow steady and the coolant stable

I 'fink I have a 25mm one in mine ????

Nige

[V8 Freak]

Interestingly while looking for the restrictor plate online I found this... It's plausible...

"We have problems on the Ginetta's (RV8)with the temparature fluctuating between 85-95'. Im told this is due to steam pockets developing in the top of the head, that does not cause the thermostat to open untill the cooler water lower down gets warm enough to open the stat itself. The cure is to drill a 4-6mm hole in the very top of the 'stat to allow any steam to escape, so the water level on the stat is always as high as possible. Dont know if this is technically correct, but it solves the problem for sure. It may just be a problem on the Ginettas as the header tank is only just above the heads."

[V8 Freak]

Not having time to blank off the various water systems to see the effect I decided on some positive action to see if we can't keep this engine alive...

Couple of things done...

Dremmel and hammer to create a restrictor plate...

The hole is approx 18 mm at it's broadest. With bleed hole and several custom gaps I recom this is near the equivalent of 20mm restriction.

Installed and took it for a nice run. Settled down just over 75 degrees C under normal dual carriageway stuff.

On the slower stuff, it drops to 70. Using the loud pedal in third on the "fun" lanes I can get it to rise to near 80 degrees...

On tickover it rises to 95, fans cut in and drop it back to 85 ish.. So, as a short term solution, it's looking pretty good and made use of one of the dead stats in the process.

A conversation with Nige and we both violently agreed the top has to come off to make sure I got holes where I expect to have them etc. All in all, that's the worst excuse ever for a new ported inlet manifold and trumpet base from V8 Developments !

The net result will be I can plumb back in a raised filler tube and have the water feed for the heater etc. where it is on most 3.9+ engines. (i.e. just under the stat)

So, a little extravagent but we will get there....

Neil