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Defurring the Cooling System
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Joined: 06 Dec 2016
Posts: 35

PostPosted: Thu Oct 12, 2017 8:19 pm    Post subject: Reply with quote

Sounds like the thermostat is sitting in cold water and not activating, might be caused by the changes youíve made to the system ie the heater bypass not being connected. Itís eventually opening with heat conduction because of the high temps. Then shutting again quickly once cooled from the rad side, keeping the temps high. Whip the thermostat out as you suggested. if all is good, take a close look at the plumbing.

Hope this makes sense, not sure how to best explain it. Came across it before, the signs and symptoms never seemed to make sense. I was eventually enlightened by someone else.
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Ian Anderson
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Joined: 19 Nov 2006
Posts: 2123
Location: Ashford,

PostPosted: Thu Oct 12, 2017 9:03 pm    Post subject: Reply with quote

Does your thermostat have a bleed hole in it to allow some bypass flow till the thermostat opens?

Perhaps time to drill a couple of 6 mm holes in the surround to let some flow

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.
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Knows His Stuff
Knows His Stuff

Joined: 28 Jan 2010
Posts: 460
Location: West Sussex

PostPosted: Tue Oct 17, 2017 7:07 pm    Post subject: Reply with quote

Thanks guys and apologies for lengthy post but last weekend I managed to do a good test run and this is the result Ö

Went on my usual afternoon run of some 35 miles on a meandering A road, very small town and then another pretty straight A road with a terrific Ďblast all the way upí hill up onto the South Downs and then a long fast open stretch to the outskirts of Goodwood. Convenient car park to turn around and back home. First part 45 to 55mph and second part 60+ if no traffic Ė and there was none!

I also set up my laptop to record the trip taking temp readings from the Megasquirt ECU for the whole journey.

First part as oil warmed up to indicated 90 degrees, water temp kept around 90 degrees. Once oil and water got to running temp, both fans came on indicating first stage at 92 and second stage at 95. (Off set at 87 and 85 but that never happened as per usual).

At mid-way point, I kept the engine running whilst I used a temp gun to check radiator temperatures. This was at least five minutes and probably nearer ten so simulated heavy traffic.

The CAI water temp gauge had been cleaned and matched to its sender by CAI a few years ago. However compared to calibrated ECU sender, it reads 10 degrees low.

Water temp gauge showed (adjusted) generally 105 except at mid-way point when it went to 110+ and basically stayed at 110 all the way home. However the laptop trace shows an different story. Running temp is generally 95 (94.7 actually) and at mid-way point reached 104.8 but then cooled back to 95 soon after starting to come back home. Hmm.

First conclusion is that once the water temp gauge gets high, it fails to return back when temperature cools so thatís why I have been assuming normal temperature is 100 to 110. Itís not. I have noticed occasionally it jumps back by 10 degrees or so but not very often

When I used the temp gun on my radiator at the halfway point, I got these results:
- Temperature at inlet around 90 degrees.
- Temperature at outlet around 40 degrees
- Temperature on right and left of rad and not covered by fan around 90 degrees
- Temperature at bottom of area covered by fan 26 degrees.

(Rad fan covers 100% top to bottom, but about 75% side to side. Rad fan is rated at a whopping 3.126 m3/hr)

Second conclusion is that whilst my engine is generally 95 and sitting traffic is 105 degrees, if I cowl the inside of the radiator to force the fan to cover as much as possible, I should get both these temperatures down. Having looked at the radiator, you can see that some 25% of the rad is not covered by the fan. Whilst things are tight, I should be able to slant the fan giving up to 40mm gap at the top and cowling the rest.

Third conclusion. Send back to CAI the temp gauge and sender to get things fixed.

So I now have another winterís project!
Photo of my Temp gauge and ECU sender locations.

Photo of my flared side panels (with just a glimpse of my TR6 Iíve just started to totally strip to fully restore).

Dax Rush 5.0l TVR V8, EFI with Megasquirt ECU and wasted spark, Racelogic Traction Control, ABS and Quaife LSD
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Joined: 18 Nov 2006
Posts: 3408
Location: Northern Ireland

1980 Ford Granada

PostPosted: Tue Oct 17, 2017 7:12 pm    Post subject: Reply with quote

That looks like a really really small need more core coverage for sure.

Although if water temp at the rad outlet, ie into the engine is 40degC, as to why there are cooling issues seems odd. That's quite a substantial drop in temperature, unless water is not flowing properly and hence a false reading.
9.85 @ 144.75mph
202mph standing mile
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