4200 CC : Problem starting when engine hot

[tonycharente]

INTERIM REPORT
I've been getting on with the replacement of the thermostat in bursts of an hour or two each afternoon due to the cold weather.
It's taken me ages, but today I managed to extract (that's the appropriate word !!!) the thermostat. Regrettably it definitely was not stuck open...
This evening I did the traditional "bringing it to the boil" test in the same saucepan as the new thermostat. The old one started to open at 82°C, the new one 88°C.
By 90°C the old one was well open, the new one barely open. At 95°C the old one was wide open, the new one only well open - it didn't fully open until 98°C.
In addition, the old one had a small by-pass hole enabling the passage of some coolant even when fully closed - no such by-pass hole on the new one.
So, ever the optimist, I am hoping that these two factors (opening later and no by-pass hole) will mean that my car will warm up more quickly so I'll no longer be getting P0128 codes and, hope against hope, the car will cease occasionally not restarting when hot.

All thoughts welcome, please.

Meanwhile I'll be attempting to put it all back together over the next few days.
Tony

 

[FIFTY]

Is the part number on the Thermostat correct?

When I did mine ES incorrectly sent the US spec thermostatbwhich has an additional hole in it for a temp sensor that isn't on the UK spec car. I sent it back for the correct one. I have a photo of it somewhere if you want I can find it.

 

[RJ237]

The thermostat that was in my coupe opened way too early; running temp of 74 on a cold day. But no starting problems, either hot or cold. Replacing it made no difference. I'm afraid you're stuck with the crankshaft sensor.

Changing the thermostat would have been a lot easier if they had used hex head cap screws instead of socket heads.

 

[tonycharente]

Is the part number on the Thermostat correct?

When I did mine ES incorrectly sent the US spec thermostatbwhich has an additional hole in it for a temp sensor that isn't on the UK spec car. I sent it back for the correct one. I have a photo of it somewhere if you want I can find it.

Thanks Fifty. Yes I have the correct Thermostat (230890) - I was aware that early North American cars had a different thermostat with a hole for a second temperature sensor, but I checked with Scuderia to make sure I'd ordered the right one. Please see the attached photos. The new one looks to be better engineered. The By-Pass "hole" looks to be some kind of one-way valve (???) but it seems to allow the passage of a small amount of water in either direction (tried under the tap).
I wonder why they they did away with it.
Thanks again
Tony

 

[tonycharente]

The thermostat that was in my coupe opened way too early; running temp of 74 on a cold day. But no starting problems, either hot or cold. Replacing it made no difference. I'm afraid you're stuck with the crankshaft sensor.

Changing the thermostat would have been a lot easier if they had used hex head cap screws instead of socket heads.

Thanks RJ237. I fear that you may well be right (stuck with the crankshaft sensor) - I'll find out in a few days time. Changing the thermostat would have been a lot easier if Maserati had thought about replacement procedures when they designed the car. Ditto just about everything else on the car!!! But perhaps it was all done on purpose to increase post-warranty labour costs. After all Machiavelli was Italian!
Thanks again,
Tony

 

[FIFTY]

Thanks Fifty. Yes I have the correct Thermostat (230890) - I was aware that early North American cars had a different thermostat with a hole for a second temperature sensor, but I checked with Scuderia to make sure I'd ordered the right one. Please see the attached photos. The new one looks to be better engineered. The By-Pass "hole" looks to be some kind of one-way valve (???) but it seems to allow the passage of a small amount of water in either direction (tried under the tap).
I wonder why they they did away with it.
Thanks again
Tony

View attachment 95794View attachment 95796View attachment 95797

Ah i see the difference now. No idea, hopefully an improved design!

Mine was quite easy to change as I did it at the same time as changing the radiator with the front bumper off so there was loads of space for activities.

 

[Oneball]

It’s just a bleed port, the bypass bypasses the radiator. Chevy v8 sometimes have them and sometimes done despite ordering the same part number.

 

[CatmanV2]

Maserati had thought about replacement procedures when they designed the car

Fairly sure they did. They just didn't prioritise them vs other things.

C

 

[tonycharente]

It’s just a bleed port, the bypass bypasses the radiator. Chevy v8 sometimes have them and sometimes done despite ordering the same part number.

Thanks Oneball, I know what you mean, but I don't think it's that kind of bypass. It's on the round thermostat disc that opens and closes according to the temperature, so it's inside the thermostat housing - no way it serves to bypass the radiator.

 

[tonycharente]

Fairly sure they did. They just didn't prioritise them vs other things.

C

Thanks Catman - you are a lot kinder than me !!!

 

[Oneball]

Thanks Oneball, I know what you mean, but I don't think it's that kind of bypass. It's on the round thermostat disc that opens and closes according to the temperature, so it's inside the thermostat housing - no way it serves to bypass the radiator.

That’s what I meant. its a bleed, stops air lock around the thermostat. It can’t be a bypass as it doesn’t bypass the radiator.

 

[tonycharente]

That’s what I meant. its a bleed, stops air lock around the thermostat. It can’t be a bypass as it doesn’t bypass the radiator.

OK, agreed. It's my (mis)use of the word "bypass" that's causing the confusion. What I meant was that the hole in the round thermostat disc that opens and closes according to the temperature enables the coolant to "bypass" the disc. Only it's not just a hole, it's a little tube that looks like a one-way valve. Anyway, no matter, Maserati decided to stop fitting them.

 

[Oneball]

The Chevy ones have got a little weighted plug in them. They’re to allow any air behind the thermostat to escape so coolant will touch the thermostat.

 

[tonycharente]

The Chevy ones have got a little weighted plug in them. They’re to allow any air behind the thermostat to escape so coolant will touch the thermostat.

That sounds like what my old thermostat has. The question still is: why did Maserati decide to do without?

 

[Oneball]

That sounds like what my old thermostat has. The question still is: why did Maserati decide to do without?

It’s the same with Chevy. You order the same part number and some come with it and some don’t.

 

[tonycharente]

Hi Tony,

Please bear in mind that I’m very new to Maserati, only owned it 2 months, so others are far more qualified than me to offer advice and probably a better way of doing it, but happy to tell you how I did the job.

So…. front drivers wheel off, arch liner out, undertray removed. The coolant sensor was hard to get at, needed at least 4 socket extensions to get a decent swing on the ratchet, but quite straightforward to do.

To do the thermostat I took off the bottom hose completely and could just get a hex socket on two of the three thermostat housing bolts from underneath the car. The top bolt is harder to get at with less room so had to use an Allen key and very patiently work the bolt out 1/4 turn at a time. This bolt was the hardest part of the whole job for me. Under the bonnet I took the top hose off at the radiator and then removed it still attached to the thermostat housing from underneath. It’s ultra tight for wiggle room but it will come out.
it’s not a hugely complex job, just no room to work and covered in cuts and bruises all over my forearms!! Need decent hex socket and Allen key. 5mm from memory.

I honestly didn’t think this would solve a hot start problem, but it genuinely did, and I’m now much more confident going to a fuel station or making any journey requiring a hot start. It has not let me down since.

Good luck with your car, I hope you get it sorted.

Ian

Hello again Ian - and anyone else who's changed their thermostat on a 4200 or GS. Another questions, please...
As reported a few days ago I managed to remove the old thermostat, with the top radiator hose still attached to it as suggested. I drained the radiator by removing the bottom hose from it (rather than risk breaking the plastic drain plug) but did not remove it entirely as by bending it out of the way I had (just) sufficient room to access the themostat bolts. I was lucky with these as once I'd managed to start undoing them (I used a 5mm allen key, extended using a 5mm socket and extension to get enough force) they undid just with my fingers. Having removed the three bolts I really struggled to get the works part of the thermostat out of the housing it bolts onto as it just kept hitting the cooling fan. Somehow I managed it, though, and then managed to wriggle the thermostat (top hose still attached) out through the wheel arch. So far so good.

I decided there was no way I would ever get the thermostat plus rubber seal back into the housing it bolts onto without attaching the rubber seal to it, so I did this using an appropriate Loctite sealant. I then got on with other things leaving the Loctite to set for a few days.

I noticed that the the top hose had not been fitted properly onto the thermostat as there was no "U" shape cut-out to enable it to go all the way onto the "U" shaped projection sticking out of the thermostat. The hose had just been pushed onto the thermostat as far as it would go. There was a "U" shape cut-out at the other end of the hose but at first I didn't realise that this meant the hose had been fitted the wrong way round, so I cut a"U" shape cut-out in the hose (in the same position, of course) before fitting it to my new thermostat. I now realise this was a mistake, and intend to refit the hose the correct way round (see https://www.ferrariparts.co.uk/part/maserati/190354?id=161876 for a photo), but the hose doesn't appear to have a way round shapewise, and certainly had been successfully been fitted the wrong way round, presumably from new.

Anyway, today I attempted to fit my new thermostat. No problem feeding it back through the wheel arch, but I have not been able to feed the works part of the thermostat into the housing it bolts onto. I know I got it out, so I know it will go back in, but how? (That's my question...)

All suggestions very welcome.
Many thanks
Tony

 

[Bails848]

Hello again Ian - and anyone else who's changed their thermostat on a 4200 or GS. Another questions, please...
As reported a few days ago I managed to remove the old thermostat, with the top radiator hose still attached to it as suggested. I drained the radiator by removing the bottom hose from it (rather than risk breaking the plastic drain plug) but did not remove it entirely as by bending it out of the way I had (just) sufficient room to access the themostat bolts. I was lucky with these as once I'd managed to start undoing them (I used a 5mm allen key, extended using a 5mm socket and extension to get enough force) they undid just with my fingers. Having removed the three bolts I really struggled to get the works part of the thermostat out of the housing it bolts onto as it just kept hitting the cooling fan. Somehow I managed it, though, and then managed to wriggle the thermostat (top hose still attached) out through the wheel arch. So far so good.

I decided there was no way I would ever get the thermostat plus rubber seal back into the housing it bolts onto without attaching the rubber seal to it, so I did this using an appropriate Loctite sealant. I then got on with other things leaving the Loctite to set for a few days.

I noticed that the the top hose had not been fitted properly onto the thermostat as there was no "U" shape cut-out to enable it to go all the way onto the "U" shaped projection sticking out of the thermostat. The hose had just been pushed onto the thermostat as far as it would go. There was a "U" shape cut-out at the other end of the hose but at first I didn't realise that this meant the hose had been fitted the wrong way round, so I cut a"U" shape cut-out in the hose (in the same position, of course) before fitting it to my new thermostat. I now realise this was a mistake, and intend to refit the hose the correct way round (see https://www.ferrariparts.co.uk/part/maserati/190354?id=161876 for a photo), but the hose doesn't appear to have a way round shapewise, and certainly had been successfully been fitted the wrong way round, presumably from new.

Anyway, today I attempted to fit my new thermostat. No problem feeding it back through the wheel arch, but I have not been able to feed the works part of the thermostat into the housing it bolts onto. I know I got it out, so I know it will go back in, but how? (That's my question...)

All suggestions very welcome.
Many thanks
Tony

Hi Tony.

From memory it was slightly easier for me to fit the thermostat housing than remove it.
One thing to note is that I fitted it from underneath, not through the wheelarch.
I'm pretty sure it didn't fit in the correct orientation, I think I got the thermostat in and then rotated the whole lot enough to get the bolt holes lined up, if that makes sense?
It will go, just trial and error I think! Good luck.

The 'U' shape on the hose caught me out too! I fitted it back as it originally came off!

Ian

 

[tonycharente]

Hi Tony.

From memory it was slightly easier for me to fit the thermostat housing than remove it.
One thing to note is that I fitted it from underneath, not through the wheelarch.
I'm pretty sure it didn't fit in the correct orientation, I think I got the thermostat in and then rotated the whole lot enough to get the bolt holes lined up, if that makes sense?
It will go, just trial and error I think! Good luck.

The 'U' shape on the hose caught me out too! I fitted it back as it originally came off!

Ian

Thanks very much Ian.

Today's "report"... I test fitted the top hose to the thermostat the right way round - only to find that it wasn't the right way round at all, as it would have pointed back towards the block, and not towards the radiator. I conclude that the hoses fitted and still supplied by Maserati are simply wrong, as they lack the "U" shaped cut-out at the thermostat end, which prevents their being properly fully fitted (as found). My cutting one was therefore the right thing to do. Closer examination revealed that there is in fact a "U" shaped projection sticking out of radiator matching the "U" shaped cut out at that end of the hose - shame I hadn't spotted that earlier.

This afternoon I spent just over three hours succesfully fitting my new thermostat.

Having struggled so much previously as already described, I decided to fit the thermostat without its hose first, which was dead easy to do - it went straight in. However the next two hours were spent struggling to get the hose in place, but in the end I got there - trial and error as you said, Ian. What worked in the end was partially fitting the hose on to the thermostat (best I could manage, everything is so cramped), then removing the three thermostat bolts (I hadn't tightened them) but leaving the thermostat in place. Like that I managed to fit the radiator end of the hose. I then put the bolts back in, tightened them and, still with a huge struggle, managed to get the hose all the way on. Even putting the lower hose back in place was a struggle, but didn't take too long.

I then poured my (very recent) coolant back in and put on my coolant pressure tester (I used approx 1 bar / 15 psi) and, joy of joys, after 2 hours the pressure hadn't dropped at all. I'll leave it like that overnight but I believe two hours with no visible drop is excellent.

I shall sleep a lot better tonight !!!

It will be a while before I put everything back together as whilst I've got the wheelarch liners out I want to adjust the headlamps and I'm not certain as to which way to turn which adjustment screws (screws not knobs). I've asked here: https://www.sportsmaserati.com/inde...-xenons-adjusting-headlamps-headlights.34855/ but despite 81 views nobody has answered my query yet.

Thanks for your help,
Tony

 

[Zep]

Sounds like you are getting there. As for the headlamp adjustment, I don’t know the answer and it seems not many others do. Could you aim the headlamp at something and turn the knobs a fixed amount to work out what does what?

 

[tonycharente]

Sounds like you are getting there. As for the headlamp adjustment, I don’t know the answer and it seems not many others do. Could you aim the headlamp at something and turn the knobs a fixed amount to work out what does what?

Many thanks Zep. Yes, that's what I'll end up doing if I don't get a reply soon.