Defender 300TDI Cooling System Issue - Pre heater related? - Defender Source
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  #1  
Old January 15th, 2018, 07:27 PM
casper222
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Nolan Tudor
1995 Land Rover Defender
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Defender 300TDI Cooling System Issue - Pre heater related?

Hey Guys,

My first post here and I am hoping I can be a larger part of this community besides, "help me with my problem" posts. I am going to try and keep this short. I have been dealing with an overheating issue on my 1995 defender with a 300TDI. It all started when the expansion tank split leaving me stranded on the highway. I have since remedied that with an Allisport aluminum replacement unit. After that I had a minor leak from one of the upper radiator hoses that I sorted as well.

The problem is that since I replaced the tank I have been having intermittent overheating issues. There is no rhyme or reason for when they arrive and it can go for days with no issues. After bringing it into my local shop they tried to bleed any air out of the system and replaced the thermostat. It worked fine for a week and overheated again. It is now back in the shop and after testing the compression in the system (seems fine) and testing for exhaust gas in the coolant they have ruled out a leak or head gasket issue.

I had a Webasto thermo top C pre heater installed before the tank split and the tech now thinks that might have something to do with the issue. When he took it for a test drive and no heat was coming out of the vents he turned on the webasto pump WHILE driving, heard some gurgling and voila, heat.

Here is the kicker, at no point has the coolant system been completely drained to ensure that all air is out of the system. Is it possible that there is still some air in the lines and turning on the webasto pump is just pushing things around the system more efficiently?

I am leaning towards doing a full coolant drain this week and filling it up via the Land Rover service manual as to make sure there is no air left in the system.

Thoughts?
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  #2  
Old January 15th, 2018, 07:47 PM
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Red90
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John B.
1991 Defender 90, 200TDI
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Well... Have you verified it is really overheating? The gauges fail or the wiring to them fail regularly. Always check with an IR gun.

Let's see a picture of how the Webasto is plumbed in? Maybe it is in backwards. It is also important the height of the unit.

These can be troublesome to get air out of due to the pump and thermostat housing being mounted too high in relationship to the tank. It relies on the little tubes from the rad and thermostat to push air out to the tank using pump pressure and not gravity. It is a really stupid design. Make sure those lines are clear and the non return valve is working on those tubes. They must be free for air to get out. Fill up the system into the radiator while parked facing uphill helps.

If this does not get you there and you want some cold eyes on your hot engine, let me know. I can probably have a look. These 300TDI overheating issues seem to happen a little too often.
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  #3  
Old January 15th, 2018, 08:19 PM
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sonoronos
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Ed
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Need to know what the actual temperature of the coolant is at operating temperature (in degrees)

"overheating" is a very vague term.

Are you losing coolant mysteriously?
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Old January 15th, 2018, 10:11 PM
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headdamage
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Andrew
exmod 90 2.5na and a 93/RRC 200tdi
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I had the impeller on my 2.5na water pump come loose, it gave me some odd over heating issues. A gimpy viscous coupling can also do this though yours sounds more like air in the system. Take Red90 up on his offer to look at it.
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Old January 16th, 2018, 01:01 PM
casper222
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Nolan Tudor
1995 Land Rover Defender
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Hey Guys,

So I picked the truck back up from the shop today and she drove fine the entire way home. Here are a couple of answers to your questions:

I have not verified at the coolant temperature level that it is overheating or with an IR gun. This is just based off the new thermostat and gauge in the vehicle (I know that they are not super reliable). It does however start running "rough" when the temperature starts to climb and there is a noticeable difference in the driveability. Any recommendations to monitor the coolant temperatures a bit more accurately?

I have also been monitoring any loss of coolant in the expansion tank and it does no seem to be losing any.

I am leaning towards doing a full coolant drain and refill to make sure no more air exists in the system.

Here are some pics of how the pre heater is installed:





Yes it is installed on the drivers side frame rail. Red90 I would absolutely take you up on your offer to come over and take a peak at it.

Cheers.
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  #6  
Old January 16th, 2018, 01:18 PM
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headdamage
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Andrew
exmod 90 2.5na and a 93/RRC 200tdi
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Nothing to do with the heating issue but that seems like hazardous location for the heater.
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  #7  
Old January 16th, 2018, 01:22 PM
casper222
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Nolan Tudor
1995 Land Rover Defender
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Join Date: Jan 2018
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Absolutely. I was not specific during the install on where to put it and the shop obviously decided that a close run to the battery was easiest for the electrical You live and you learn. I am either going to change it to under the hood in the future or get a beefy skid plate made up for it.
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Old January 16th, 2018, 01:24 PM
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sonoronos
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Wait, wait...are you meaning to say that the overheating problem started when the pre-heater was installed?

Duct tape a meat thermometer from your kitchen to the outside of your radiator hose?

Another thing you can try is to bypass the pre-heater and get it out of the loop.

But measuring your temps is the first step. If you're not losing coolant then I'd rule out the headgasket.
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  #9  
Old January 16th, 2018, 01:50 PM
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Red90
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John B.
1991 Defender 90, 200TDI
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So the Webasto is installed after the cab heater. I can't tell if it is plumbed to pump in the correct direction from the pictures. Normally people plumb it in before the cab heater to help warm the interior.

Go to Crappy Tire and get an IR temperature gauge. When it gets up to temperature, stop and measure the temperature where the thermostat housing is attached to the head.

For long term measurement, a VDO vision gauge and sender is a good idea or a MadMan engine monitoring system. Anything is better than the stock Lucas gauges.

To make sure the automagic air purge system is working feel the the little line coming off the thermostat housing. It should be hot when the engine is up to temperature.
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