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I discovered my recently purchased Midas didn't have a thermostat - the engine got cooler the faster you went.

I've fitted an 88 degree thermostat, but now there's a problem. The electric fan starts running before the temperature guage is even half way and the temperature keeps climbing to the red, eventually it spits out water from the overflow tank.

I've checked for airlocks (twice), theres a square key bleed on top of the thermostat housing. So have I got a faulty thermostat, bought too high a temperature or is there something else I'm doing wrong?

This was meant to be the simple job before I tried to sort the other running problem.

Looks like a faulty thermostat. Did you check if it opens in boiling water? I find these things very unreliable. I have changed quite a few in the past.

Yes it could be thermostat.....but it could also be blown head gasket. I know this from past personal experience....especially if its one of the large over bores.

Check the cheap and easy things first though.

Kind regards,

David

Stupid question..... is it in the right way round? Been there, done that.

That aside, that fact it was missing is suspicious, it's not like they just fall out is it? Head gasket or cracks between valves could be possible suspects, what's the other running problem you have?

Rich

Well seeing as it ran fine at tickover without a thermostat I'm going to suspect a faulty thermostat and have ordered an 82 degree one this time. Before I installed a thermostat the electric fan used to cut in and out fine at tickover with no sign of overheating. I tried running the engine with the plug on the top of the thermostat removed and I'm not convinced the thermostat is opening properly, if at all.

The other problem I have will probably be the subject of yet another thread, the car drives fine in first and second, feels a bit flat in third and then starts to cough and splutter in fourth with the occassional surge of power. It's most likely a fuel problem as the last owner had just fitted a secondhand HIF44 and an electric fuel pump. Reverting to a mechanical pump hasn't changed the symptoms, but I will try an alternative carb once i have the thermostat sorted.

its also worth checking what head you have.

The spi heads (not to be confused with the mpi heads which are also different) were known to have slightly different water galleries, as well as a blocked up termperature sender location (which can be drilled out and tapped to allow fitment) as it picks it up from elsewhere on the spi.

A known work around for the thermostat on these spi heads is to drill several 6mm holes around the thermostat ring so that it lets through some extra flow at all times.

Not having a thermostat at all is also bad, as it stops (or rather slows) flow to the further parts of the head (number 4 cylinder), causing hot spots.

Then I'd start by taking out the thermostat and boiling it in a pan to see if it opens at all, as suggested above. If it doesn't open before things start to boil you have your answer.

Does the heater get hotter as the temp goes up, does it vary or stay cold?

yes the heater does get hotter as the temp goes up, although a working thermostat does attempt to moderate this as it opens and closes to adjust the temps, wont stop it climbing though if theres another issue.

Blockages in the heater can also cause temperature to rise....due to general sludge or that nasty bodge stuff called radweld.

skip_rat wrote:The other problem I have will probably be the subject of yet another thread, the car drives fine in first and second, feels a bit flat in third and then starts to cough and splutter in fourth with the occassional surge of power. It's most likely a fuel problem as the last owner had just fitted a secondhand HIF44 and an electric fuel pump. Reverting to a mechanical pump hasn't changed the symptoms, but I will try an alternative carb once i have the thermostat sorted.

I have had a Midas with a similar experience twice with different solutions:
The first one I found the electronic ignition module on the distributor to be the cause. It works fine at idle (ignition timing is no problem), but under full load (that is in the higher gears) it would fail intermittently. Revving the engine at stand still does not reveal it, you need put load on it by taking the car on a quiet road, put it in second gear, get it rolling and then full throttle. If the ignition module is faulty it won't accelerate evenly or might even splutter.
Before I found this I also had replaced the fuel pump, replaced the air filter and fuel filter etc.

The second occasion was caused by a wrong carb needle. The previous owner had installed an MG filter but the needle was standard. Replacing the needle with an MG one completely changed the performance. I recall Adrian Dodd helping me with this one.

Rich wrote:Stupid question..... is it in the right way round? Been there, done that.

Yesterday I found out that I had made the above mentioned mistake
My car was warm in the summer, but last drive in September the car stayed cold. I assumed a faulty thermostat, bought a new one and unbolted the thermostat housing. When I had removed it I noticed the thermostat was sitting the wrong way around!
I tested it in hot water and it worked fine. Lucky because the new replacement unit didn't fit.