300Tdi Radiator - The hole inside under the bleed hole.

[tweetyduck]

Inside a 300TDi theres a bypass hole half way down directly under the bleed hole. IIRC some Australians block this off or make it smaller so more water goes round the rad thus giving more cooling. I cannot recall if they blocked it off or made it smaller.

My problem if i keep overheating and if i measure the temp at various positions on the rad it does seem a lot of hot water is bypassing the radiator veins/fins/whatever you call it. The water goes straight down the rad and out the bottom.

If i open my rad again and fix a small piece of aluminium over the hole with epoxy do you think I will get better cooling ???

I was thinking of a strip of aluninium about 10mm wide directly across the middle leaving each side of the hole free. Anybody heard of this or even done this ?

[mmgemini]

You should have asked Johan this question when you were in his workshop at Keetmamshoop as I should have listened to him more

I believe the make the hole smaller. Also they sometimes add another block on the other side of the rad.

Did you follow the filling sequence correctly when you filled up the rad ?

[rick]

My rad bloke reduces the bleed to 1/8"-3mm, some close it off entirely.

Why Land Rover made it so large is anyone's guess, why they've done more than several things over the years not even a couple of Australian Land Rover engineers have been able to tell me, they reckoned Solihull was a different planet sometimes......

[Rooiels]

Tweetyduck you are experiencing the exact same problem that I have just recently managed to resolve. After struggling with an overheating problem for years, I installed inlet and outlet sender units on the radiator (4 core type) and could never get a better cooling differential of more than 20degree C. Using the AC reduced this to 15 degrees. When towing or going up a mountain pass was a nightmare. The temperature would just keep going up! My dash board looks like a cockpit in a Spitfire, I monitor all possible temperatures oil, water exhaust gas. In desperation I got fed up and was about to order a aluminium custom made radiator. I then discovered when dismantling the radiator that although the infamous bypass hole has been reduced from 13mm to 3mm, the baffle where this hole is does not meet up with the radiator cores in the header tank which as you know is on its side. The clearance here was 6mm across the width of the cores. This means that there is a bypass of 6x80mm which is equivalent to a hole of 25mm as opposed to 13mm.The volume of water flowing through this is not twice but 4 times as much. Since I have solved this issue, the cooling differential is 30 degrees C and I can tow etc without problems.

Good luck with your radiator.

[tweetyduck]

So i've closed the hole with part of a Bean can....yes a can of Beans....not Baked Beans but Chilie Beans, after all we are in South America.

Thanks all for the advice....and yes Mike I should listen more....but that means I need to ask the right questions !

The Rooiels post is spot on there is a large gap at the side of the baffle so this isn't sealed and lets the air past when filling. The gap is about 2mm for the width of the baffle so i think theres still a serious bypass there. Anyhow, I will see how she goes. It took slightly longer to bleed due to this issue.

The metal is glued in place with expoxy put into position with a telescopic magnet (the thing i use to pick up bolts from the engine mounts when i've droped them in) I sanded the baffle and the bean can to key the glue so hopefully it holds. Also the can is too large to go through the hole and cause havoc with the water pump. At least I hope it is !!! The flow is downwards isn't it....

[Daan]

Anyone any pictures of this, or a link? I cant picture the problem or the solution!

Daan

[Maverik]

Anyone any pictures of this, or a link? I cant picture the problem or the solution!

Daan

My thoughts too... anyone got any diagrams?

[tweetyduck]

I considered taking a photo but it was impossible to get a good shot.

Half way down the rad inside the right hand side reservoir is a metal baffle with a hole in the centre about the same size as the hole at the top where the plug screws in. You know the plastic or hopefully brass plug at the top. The one where you bleed the rad. Direclty under is the hole in the baffle. The baffle only goes across the reservoir.

The baffle is I suspect intended to divert hot water entering the top of the rad through the rad to the othere side. There it travels down and back the the same side as it entred and out the bottom hose. Top 50% of the rad is thus hot water going left and the bottom 50% is cooler water going right. Problem is the baffle's lager hole lets a lot of water bypass the rad core. The water enters the top and goes straight down to the bottom. The baffle also does not seal the side of the rad even when the hole is covered as it does not meet up with the side of the core inside as to seal this gap between the baffle and rad core fins would require some tricky soldering of use of silicon which they would almost certainly never use in a new rad.

You can take a look at it by partially draining you system. Done carefully you loose little coolant. I drain mine using a cork and the larger of the hoses to the header tank. Pull the hose off and stick your finger over the header hole to stop losing all the coolant in the header, at the same time raise the hose to a higher position. Stick in the cork in the hose so you can move it into a bucket under the car. An assistant will keep their finger over the hole in the header when you do this. Once you've drained the hose put it back on the header to let the rest of the header water drain into the rad and then using the same cork drain the remaining water into the bucket using the hose proceedure again. You'll loose about 500ml max. I've got this down to half a cupfull.

[Maverik]

Now I understand, as the upper and lower coolant pipes are attached to same saide tank, unlike the 200tdi...

I can't see it being an issue blocking it up, intrested to see what difference it makes to your cooling, as long as the area for the cooling tubes are cumativly larger than the mid baffle leakage area's then there will be negligable leak through i think... also when you look at the radiator, the lower hose is a narrower diamemter than the input hose too, this would I think help avoid side tank baffle leakpast too...

Mav

[Rooiels]

To see where this baffle plate is, is very easy. You don't have to disconnect any hoses. Simply use a length of 10mm PVC tubing and first siphon water out of the header tank into some empty cooldrink bottle. Once this is empty then you can open the filler plug on both the radiator and the thermostat housing. Push the tube into the radiator and continue siphoning the water out. When finished use a torch or if you have a mechanic thin probe light shine down the hole and you will see the baffle with the hole in it. You could also use a bright LED connected to a battery and drop this down the hole to see inside.Your fix using the bean can and glue is not recommended. The hot water at 92degrees and the glycol antifreeze mixture will dissolve your glue an render the mod useless. The only way to solve this is to remove the radiator, take it to a radiator works and ask them to do it properly by soldering a brass plate over the hole and close the core to baffle plate as best as possible. At the same time you can then confirm whether your cores are clear and functioning correctly. Sediment tends to block the cores with the passage of time. At the same time you could fit a fitting on the bottom of the radiator above the outlet nipple so that you can fit a temperature gauge and sender to monitor your return water temperature. This is a bulletproof mod and works well for me. Have you considered also fitting a www.littleblackbox.co.za I have this and it is worth its weight in gold.

Good luck

[Rooiels]

Just to add to my last posting, when refilling the radiator, I follow the following procedure. I fill the header tank first to the brim then leave it to allow the water to siphon down to the radiator. I then fill the radiator till the water is right into the neck and quickly screw in the plug. Next I fill the thermostat housing also to the neck and screw in the plug. Having done this I then fill the header tank again to 25mm above the plimsoll line in the middle of the tank. Screw the tank cap on and go for a short run of 10km making sure that I drive uphill and down hill. Preferably would be an off road track. This ensures that the air, that may be lurking somewhere is bled out. Back home I check the level in the header tank and usually find that it is at the plimsoll line. Cheers