Sudden overheating

Chaps,

Have a very odd one, car has the thermostat in line mod.
All seems fine apart from now on two occasions it has suddenly gone from normal to red hot in around 5 seconds, pull over, fans are both running, drops back down again in says 30 seconds.
Has done this twice after being driven 35+ miles. Done about 200 miles since the mod was put in.
So today it went out with the dogs say 2 miles, sat for a bit, then 19 miles at speeds of up to 70 to town, then 2 miles around town, stopped, drove back 18 miles again high speed then suddenly shot up.

Expansion tank was clearly boiling, coolant over the engine and the level had risen to the overflow tube. Not apparent links in the coolant system hoses. When called down to gauge reading mid way normal had no fluid in expansion tank. Topped up drove back the last 2 miles with no issues at all.

Was thinking air in systems causing a block?

Or am I way of, was thinking of changing the expansion tank cap!

Open to ideas.

its a TD4 2005.

titchfield9 said:

car has the thermostat in line mod.

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How long has the in line (Renault 5?) thermostat mod been in there?

Been in there a couple of weeks, say 3 weeks cars not driven much mainly weekends.

Perhaps you still have air in the system

That's what I was think, not sure how to get it out.

titchfield9 said:

Been in there a couple of weeks, say 3 weeks cars not driven much mainly weekends.

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Did you put the sensing bulb towards the engine side of the top hose? Did you make sure the small hole or V slot was towards the top, so air trapped in the hose can bleed to the tank?

titchfield9 said:

That's what I was think, not sure how to get it out.

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Silly question, of course, but you have opened and let air out of the screw-plug close to the bulkhead by the relay/fuse boxes?

Just made myself a inline thermostat housing with an 88C Citroen/Renault thermostat on my 2004 Freelander Td4 (yesterday) and I'm also checking the level in the expansion tank on a regular basis.

From cold take the expansion tank cap off and turn the engine on you will see air bleeding out the return pipe into the tank then it will just vent out the tank neck. When you feel the warm is getting to warm put cap back and turn off engine and repeat if it needs it. Did you replace the rad fluid with new when you did the stat?

Thanks, didn't know about the bleed screw, just checked that and its running coolant.
To answer the other questions further up, its a custom made CNC machine in line housing with the new stat in side so not sure what is inside it.

As its fine for the majority of time hence why I was also think air in the system.

I just topped the system up via the expansion tank, put the cap on and warmed it up, then topped it back up.

titchfield9 said:

To answer the other questions further up, its a custom made CNC machine in line housing with the new stat in side so not sure what is insid

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It'll have a cheap, standard style thermostat in the housing.

There was another forum member that had one of those fitted. I believe he also had problems with overheating. I can't remember what the outcome was.

The thermostat inside the housing will have a side that goes to the hot engine side. If it's the wrong way round, it can't sense engine temperature.

It's also possible it has an air bleed, which needs to be at the top. If it doesn't have an air bleed, then the best thing to do is drill one.

Thanks all, the company who supplied it say it has a bleed hole inside...….
When I asked if its 'marked on the body where it is' got no answer so will take it out and check it at the weekend.
Possibly change it for a better one.

Will follow the procedure above to bleed it, this time trying not to drop the bleed screw down the back of the engine.

titchfield9 said:

Thanks all, the company who supplied it say it has a bleed hole inside...…

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Make sure the hole is at the top, when in it's final fitted position.

titchfield9 said:

When I asked if its 'marked on the body where it is' got no answer so will take it out and check it at the weekend.

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You can look for the sensing bulb and fit that at the engine side of the hose.

titchfield9 said:

Possibly change it for a better one.

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That's going to make the £10, R5 thermostat mod very expensive.