Radiator.... Hot at Top but Cold at Bottom

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dooley1414
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#1 Radiator.... Hot at Top but Cold at Bottom

Post by dooley1414 » Sun Apr 22, 2018 7:47 pm

Hi all.... any one got any ideas put my Recon. Rad. on new thermostats new Revotec Fans.... new Hose Kit.... started her up got to Running temp. Fans cut in and out had her ticking over for 20 or so minutes.... but when I touch the Top of Rad. it's really Hot.... but the Bottom is Cold.... Hot air is coming from the Heater.... I cant take it down the road for a good drive because the bònnet is still off it.... anyone got some ideas why it's Hot at Top and Cold at Bottom and how to fix? Many Thanks In Advance.... Des.
Ex. Texas Import 1971 Series 3 V12
Des. Suffolk.

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politeperson
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#2 Re: Radiator.... Hot at Top but Cold at Bottom

Post by politeperson » Sun Apr 22, 2018 8:49 pm

Has your water pump got an impeller on it?

Mine didnt! It corroded away. I had almost no water circulation.
James

L.J.K. Setright was right.
"You just cant beat a good E-type"

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#3 Re: Radiator.... Hot at Top but Cold at Bottom

Post by dooley1414 » Mon Apr 23, 2018 6:53 am

Hi.... Reconditioned Waterpump to.... forgot to mention that.... Des.
Ex. Texas Import 1971 Series 3 V12
Des. Suffolk.

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christopher storey
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#4 Re: Radiator.... Hot at Top but Cold at Bottom

Post by christopher storey » Mon Apr 23, 2018 8:43 am

Is your radiator horizontal tubed or vertical tubed ? If the tubes are vertical then hot at top and cool at bottom is exactly what would be expected. Even with a horizontal flow it does not sound that unusual to me

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#5 Re: Radiator.... Hot at Top but Cold at Bottom

Post by Ole-xke1974 » Tue Apr 24, 2018 11:54 am

As mentioned by Christopher, your radiator has vertical core and will initially feel hot at the top and cool at the bottom, but after a few minutes, especially when running the engine standing, the radiator should get equally hot top to bottom. That's when your otter switch reaches the temperature where it supplies a ground to the radiator fan relay.
When first starting the car cold, have you felt or measured the temperature on the two coolant hoses running from the thermostats to the radiator ? They should stay cool and at the same time get hotter when the thermostats open up.
Maybe your radiator is clogged up, preventing proper circulation ?

Cheers ........ Ole
1974 SIII E-Type w. XJ S2 4sp w. O/D

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#6 Re: Radiator.... Hot at Top but Cold at Bottom

Post by lowact » Wed Apr 25, 2018 12:58 pm

The radiator hot on top suggests there the thermostats are working properly, have opened enough to allow at least heat convection from the engine despite no flow thru the radiator. Hot above, cold below is consistent with blockage on the outlet side of the radiator, heat convection warms the top but heat only flows up, not down, unless there is flow. An outlet hose blockage would stop flow through the radiator just as effectively as a blockage anywhere else. The fact that the fans come on is weird, as Ole says, the temperature sensor is at the bottom so if it really is cold down there, how come the fans turn on? With yr new Revotec fans, is the temp sensor moved to top side? Yr new hose kit, is it all connected the right way around, could there be a kink in a hose or something similar? Is the hose arrangement the same as original, from the radiator to the water pump via the oil cooler? With the car stopped, pinch/squeeze the radiator outlet hose, just to get a feel for how easy it is. Repeat with the car running. It should be almost as easy. If the pipes are hard (pressurised) it might ???? mean there is some blockage/restriction between the radiator outlet and the pump? Or maybe there is an air lock although I cannot imagine how, try running for a bit with the heater hose disconnected this might ??? clear any air lock? If there is no blockage or air lock it must be the pump, do u trust who reco’d it?
Regards,
ColinL
'72 OTS manual V12

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#7 Re: Radiator.... Hot at Top but Cold at Bottom

Post by dooley1414 » Fri Apr 27, 2018 7:52 am

Hi all thanks for all your recommendations.... with my Revotec Fans the temperature sensor is topside so I would imagine that's why the fans are coming on.... at operating temperature the temperature gauge says about halfway when the fans cut in. I have the bonnet on now I am taking it to a garage today to make sure the brakes are pulling up straight and firm for the MOT standard.... it is going to be a little few mile run I hope maybe it will prove successful that the radiator warms up top side and bottom. I will let you know my findings.
Ex. Texas Import 1971 Series 3 V12
Des. Suffolk.

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Ole-xke1974
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#8 Re: Radiator.... Hot at Top but Cold at Bottom

Post by Ole-xke1974 » Fri Apr 27, 2018 8:34 am

dooley1414 wrote:
Fri Apr 27, 2018 7:52 am
with my Revotec Fans the temperature sensor is topside so I would imagine that's why the fans are coming on.... .
My suggestion is to either move the sensor to the bottom or if possible, use the original otter switch. As an FYI, there are replacements available for the otter switch. Both original and ones using modern temperature switches.
The reason for having it in the bottom is that it will ensure that the return water has a temperature that will have your engine running within the designed temperature range. If you control the fans based on the temperature at the top the fans will most likely come on too soon and not take into account that the air passing through the radiator when driving is providing sufficient cooling. As a result, your car will run too cold.
Unless I have missed something.

Good luck with your MOT.

Cheers ........ Ole
1974 SIII E-Type w. XJ S2 4sp w. O/D

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#9 Re: Radiator.... Hot at Top but Cold at Bottom

Post by lowact » Fri Apr 27, 2018 11:34 am

I'd fix the cooling before going for a drive. Only reason for imagining that it will be ok was yr fans coming on, now we know the reason for that. Trust yr temp gauge, if it crawls past normal stop immediately, there is nothing cooling u down.
Be good if, before driving, you ensure that there is flow thru the radiator. If not or anyway, you could check the pump: Take the belts off the water pump pulley and try spinning the pump, does it feel like there is water in there? might the impeller be loose on the shaft? Etc.
Regards,
ColinL
'72 OTS manual V12

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MarekH
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#10 Re: Radiator.... Hot at Top but Cold at Bottom

Post by MarekH » Sat Apr 28, 2018 6:39 am

Radiators are supposed to be colder at the bottom than at the top - that's their designed job. Not all of the water flow is guaranteed to be evenly distributed from left to right however and the tubes at the edges may well be relatively cool compared to the tubes towards the centre.

You probably just had a minor air lock first time around.

A properly positioned Otter switch to control the fans and make them cycle means that the exit temperature of the water is varying by ~10'c from about 82'c to 72'c. Relocate your Revotec fan switch to the bottom of the water exit where Jaguar had it and expect it to target ~73-76'C for a car with 82'C thermostats. Remember the same basic engine is fitted to many more cars, with 88'C thermostats and less space for air cicrculation "under the hood" and yet they do not overheat on a day to day basis if the car is maintained.

I would argue that there is nothing wrong with a properly maintained system for the s3 in the first place and that you are simply putting more electrical strain on your car by using these current hungry aftermarket fans.

kind regards
Marek

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#11 Re: Radiator.... Hot at Top but Cold at Bottom

Post by dooley1414 » Wed May 09, 2018 8:43 am

Hi all just an update on the hot top cold bottom radiator issue I went for a good long run with the Ipswich to Felixstowe Classic car run on Sunday a really hot day lots of stop start traffic because there is so many classic cars on the run and the temperature gauge did not show anything over standard operation temperature although the fans were cutting in early as I was not sure whether to set it at about 75 76 degrees C so I think they were coming on around 70-72. So next time I take it for a good run I might set it a little bit higher and see what happens Cheers any thoughts? Thanks.... Des.
Ex. Texas Import 1971 Series 3 V12
Des. Suffolk.

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#12 Re: Radiator.... Hot at Top but Cold at Bottom

Post by christopher storey » Wed May 09, 2018 8:55 am

If it cooled itself well in fairly adverse conditions , why not leave well alone ? It is far better to have the fans coming on a little early, than too late

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