Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Thermostat

Evening all,
Wonder if someone might be able to help me.
Thermostat on my 2008 4/4 1800 duratec moggie is sticking open. Takes longer to heat up, doesn’t get as hot as normal, but fan does come on occasionally for a brief blast. Ford number on thermostat housing 4L5G-AE
Got a replacement one, a Gates , TH45190G1, with 90degree opening. Fitted it and tested it. Gauge sat smack on 90 again, bottom rad hose felt as though it was changing temps, but the fan came on relatively quickly and wouldn’t go off unless I switched off the engine and let it cool that way.
Any ideas what the temp setting should be?
Any ideas of a “ good” replacement item?

I have asked at the local ford dealer but they claim they can’t help me as their computer needs the car model, and not just the engine details.

Many thanks in advance.
Gaz

Gaz, there is a current TM thread on a similar issue with another 2008 4/4 here. An 85°C thermostat was used as a replacement. Note also the common issues with 4/4 models fitted with larger aftermarket aluminium radiators.

Hi Richard,
Thanks for the reply.
I have the feeling mine is opposite to the the other thread as I have no high temps involved and still have the original radiator.
I had gone through various threads and found some using the 90 degree thermostat, hence why I tried that but 85 would make sense, just typical that I haven’t seen one of them yet.
When I looked up the part number on the thermostat, it has always come back as a Mondeo, 90 degrees.
Gaz

Has the radiator and the cooling system been flushed through and new antifreeze and water been added, just to ensure there is no sludge build up in the radiator etc restricting flow, which can happen with cars over time and those subject to periods of inactivity. It's one of the first things I get done when I purchase a Morgan, as invariably like spark plugs and brake fluid changes is not always attended to as it should be.

Hi John
Coolant has been changed in last couple of years and was flushed.
Surely if the rad was blocked with sludge the system would tend to overheat rather than over cool.

Indi, everything john has said is spot on! first question.... have you recently acquired the car or is it a long term ownership car that has just started doing this.

Flushing... not just a water flush but a chemical flush is needed. You'd be surprised how much gunk will be sticking around in the pipework and galleries of the engine, Your car is 30 years old and as Mr. Harris said things do tend to get neglected on cars that don't do many miles! First I would dump whatever coolant you have in there and fill with water and Prestone coolant flush (one litre) and fill with water. there are all sorts of advice here but I would do it for a weekend, start Friday night or Saturday morning and fill the system with the solution. Run the car stationary for about an hour at operating temp then if it doesn't show any leaks go for a blast for an hour, repeat the next day. When the engine has cooled down drain out the system and stand back in shock at the crap that is coming out and the colour. Now repeat with plain water, a stationary run is fine for that and id suggest that about three goes with plain water will be required. When you are happy I would remove the thermostat and using a hose flush the rad both ways and the block too. When all is to your satisfaction fit a new stat inspect the hoses and refill the system using the correct anti-freeze and distilled water. Important to use distilled water but more so in a hard water area, Don't worry about that though when flushing as like a kettle in hard water it takes a while to build scale!
Opie oils stock the correct anti-freeze and distilled water, post free it will cost roughly £70 delivered to your door.
On a standard cooking engine I don't believe a stat of 85' or 90' will make much difference if all is working correctly. The only other thing you may have to investigate at this stage is the water pump. Some have plastic impellers and they can self destroy as they get older or even gum up around the blades and the pump is then just cavitating and not assisting the flow around the system. Oh! just one thing more, if on the initial drain its very mucky just do one quick flush before introducing the chemical flush mix as you want the chemical to work on the stuck grime and not on the stuff in free suspension which has been left behind. Best of luck!

Hi Sewin,
Thanks for the reply
I have had the car for the last 17 years, since new, and thermostat started to play up end of last year.
She has never over heated, even when I fitted the 90 thermostat, just the fan stayed on.
Even when down in southern Italy last year she never cooked and the fan came less on and off as expected.
Biggest problem I have is trying to get the correct replacement thermostat. I thought it was 90 like the mondeo but maybe that was just a bad thermostat

Forgot to say, put the original stat back in and temp sits happy at 80-83, except as it cools in the evening the. Drops to around 70. There is a noticeable loss in cabin heat compared to the 90 stat that I had in

Are you putting the heater on when the ambient temperature drops, or does the heater remain off when you experience the temp drop at night? As the use of the heater also effects the amount of water circulating through out the system and can effect water temp. Does the heater always blow hot? In the past I experienced a heater blowing cold/cool when the head gasket had gone or had a slight radiator leak. enough to allow stream to escape. Is your heater matrix and hoses etc ok? Are you losing any coolant? Any evidence on the flour or around the engine of coolant loss staining.

Not 100% sure on a 2008 4/4 but later models have the full amount of coolant circulating all the time. This because the heater core is permanently fed, with dash cabin heat control operating flaps in heater/air box which adjusts the mix.