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Old 19-07-2019   #1
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Coolant is boiling!

A couple weeks ago my 2002 Doblo 1.9 JTD started losing collant.

Took it in and had the water pump and hosing replaced, new thermostat and new rad and expansion tank.

She was running fine for a couple days then started over heating again. When I pull over, the collant is boiling in the expansion bottle. By the time it cools down, the bottle is empty so I'm filling it with water.

This has been the cycle for a week now. Check in the morning, bottle empty. Drive 20 miles and it over heats, bottle empty. No evidence of a leak anywhere. Engine oil is fine (good color) and level never changes.

The mechanic seems to think it might be the cap on the exp tank so new one on the way.

Has anyone seen this before?
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Old 19-07-2019   #2
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Re: Coolant is boiling!

Have you had a compression test done or a chemical test of the coolant which tells you if their are products of combustion in the coolant.

A head gasket problem seems most likely at this point.

Bear in mind that the cap on the coolant bottle is a a fail safe not part of the regular running of the system, it should not be regularly venting the coolant.
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Old 22-07-2019   #3
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Re: Coolant is boiling!

Yeah I'm starting to think the same.

Weirdly....

If I keep the RPMs down below 2500 (which is too damn slow for me BTW) she doesn't overheat. Still looses coolant, but takes a week to notice.

SO yeah, I think the head has a very minor leak, somewhere impossible to see, not effecting the oil paths.

I'll keep ya posted
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Old 31-08-2019   #4
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Re: Coolant is boiling!

UPDATE

So I took it to another mechanic who looked at the resevouir cap and said it's the wrong cap. A trip to the Fiat dealer (and £45 lighter) replaced the cap and it ran just fine.

Until it got to 32 degrees in Milton Keynes. On the motor way home it pegged the gauge again. Coolant boiling like crazy.

So a compression test shows factory results! Engine oil is a nice gold color.

I dunno....completely at a loss. It's like the engine coolant just stops flowing and starts boiling. It's weird. It will run fine for weeks. Heavy load, thrashing it almost, and be just fine. Then at a steady 70mph motorway driving 3k rpm and it pegs!

Gonna take it in and have the guys remove the thermostat. I forgot to mention in the OP the radiator, water pump, water pump housing and hoses have all been replaced. The only part left is the heater core.
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Old 31-08-2019   #5
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Re: Coolant is boiling!

It won't be the heater core.
Are there any signs of coolant like stains anywhere?
Put the end of the coolant tank ocerflow pipe in an old plastic drink bottle to see if anything is coming out (the overflow is right under cap, if it's just a spigot add abit of pipe).
Most likely though it is a leak in head area from the coolant to the exhaust, probably through the head gasket into the cylinder. A good garage will have a tester to check for exhaust in the coolant (a tube with detector fluid that fits in place of the header tank cap.
There is a slight possibility that one of the new parts fitted was faulty, improperly drilled therostat housings have been reported. Get an exhaust gas in coolant check and Coolnat pressure test. If both of those are OK take the thermostat houing off and check carefully.
Problem is evertime it has overheated is putting stress on the head and head gasket so even it wasn;t the original problem it might be now.
If there is no exhaust in the coolant, it passes a coolant pressure test and a double check of the thermostat is OK then it's time to take the head off.

Robert G8RPI.
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Last edited by g8rpi; 31-08-2019 at 17:14.
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Old 02-09-2019   #6
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Re: Coolant is boiling!

There is a possibility even with a new pump, and especially because they have plastic impellors that the pump has in some way broken up, lost some of the vanes off the impellor, this would in some way go with your reports of not having problems when thrashing it.

When thrashing it and moving quicky you generate some more heat and you move a bit quicker so more air flow but vitally the engine revs are high and so is the speed of the water pump pushing more water round.

If a cheap replacement pump was used its even more likely to break.
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Old 03-09-2019   #7
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Re: Coolant is boiling!

Quote Originally Posted by LeadMagnet View Post
UPDATE

So I took it to another mechanic who looked at the resevouir cap and said it's the wrong cap. A trip to the Fiat dealer (and £45 lighter) replaced the cap and it ran just fine.

Until it got to 32 degrees in Milton Keynes. On the motor way home it pegged the gauge again. Coolant boiling like crazy.

So a compression test shows factory results! Engine oil is a nice gold color.

I dunno....completely at a loss. It's like the engine coolant just stops flowing and starts boiling. It's weird. It will run fine for weeks. Heavy load, thrashing it almost, and be just fine. Then at a steady 70mph motorway driving 3k rpm and it pegs!

Gonna take it in and have the guys remove the thermostat. I forgot to mention in the OP the radiator, water pump, water pump housing and hoses have all been replaced. The only part left is the heater core.
How did you get on in the end with this issue?
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Old 03-09-2019   #8
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Re: Coolant is boiling!

@g8rpi

All good points and thanks. Everytime it goes in I have them do a pressure test. Always factory numbers. They have tested the exhaust for a leak with "all in the green" results. There's never a drop of coolant on the ground, but when you open the res tank it's just steam pouring out so always have to fill it. Spent a small fortune in antifreeze!

You might be right on the water pump and thermostat being faulty.

@AndyRKett

Yeah based on yours and g8rpi I'm gonna have the water pump replaced again. The Fiat OEM pump is only £40 and while there at it have them yank the thermostat and inpect the housing, but that therm is definitely NOT going back in.

@everson38

IRL is kicking me this month. I hope to get it in this week (2 Sep) or next at the latest. I'll be sure to post the findings.

Thanks guys!
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Old 25-09-2019   #9
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Thumbs up Re: Coolant is boiling!

THE FINAL UPDATE!

First off, a huge (with a wet sloppy kiss) thanks to everyone who posted suggestions. This problem has taken me almost a year to nail down and your help was epic.

So I need to back up about 2 years ago. At the time, a local mechanic was looking after the Fiat and several other vehicles. After complaints from my family about the quality of work, I stopped going there. That was a year ago.

On Monday, I took it in for the "new" mechanic to replace the water pump, thermostat housing and main cooling hoses off both. These had been replaced 2 years ago by the "other" mechanic.

What he found was jaw dropping. The water pump that was installed was the biggest POS either of us had seen. Plastic impeller, steel trans rod (which was rusting), the main seal was weeping, the pulley surface was badly scared. The timing belt (which powers the water pump) was the correct size, but wrong type for the Doblo. The belt showed heavy wear and scoring along it circumference.

Basically, my old mechanic changed the water pump and timing belt with the cheapest junk he could get and charged me premium price.

The heavily worn timing belt was slipping on the water pump. The water pump itself was slowly destroying it's impeller and seals due to poor quality.

These two combine caused the cavitation in the cooling system, loads of air, resulting in the coolant boiling when at temp.

My new mechanic has installed the best water pump we could find as well as the best timing belt. Knock on wood, everything I have tried that would previously caused it to over heat has resulted in......nothing......temp guage glued to the half way mark (except when cold, but you get what I mean!)

In total, this has cost me about £1500 with the radiator, water pump, thermostat housing, cooling hoses, reservoir and three res caps being replaced.

She's running great, feels great, can't wait to take her back to Italy after being sidelined for a year!
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Old 25-09-2019   #10
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Red face Re: Coolant is boiling!

Quote Originally Posted by LeadMagnet View Post
THE FINAL UPDATE!

First off, a huge (with a wet sloppy kiss) thanks to everyone who posted suggestions. This problem has taken me almost a year to nail down and your help was epic.

So I need to back up about 2 years ago. At the time, a local mechanic was looking after the Fiat and several other vehicles. After complaints from my family about the quality of work, I stopped going there. That was a year ago.

On Monday, I took it in for the "new" mechanic to replace the water pump, thermostat housing and main cooling hoses off both. These had been replaced 2 years ago by the "other" mechanic.

What he found was jaw dropping. The water pump that was installed was the biggest POS either of us had seen. Plastic impeller, steel trans rod (which was rusting), the main seal was weeping, the pulley surface was badly scared. The timing belt (which powers the water pump) was the correct size, but wrong type for the Doblo. The belt showed heavy wear and scoring along it circumference.

Basically, my old mechanic changed the water pump and timing belt with the cheapest junk he could get and charged me premium price.

The heavily worn timing belt was slipping on the water pump. The water pump itself was slowly destroying it's impeller and seals due to poor quality.

These two combine caused the cavitation in the cooling system, loads of air, resulting in the coolant boiling when at temp.

My new mechanic has installed the best water pump we could find as well as the best timing belt. Knock on wood, everything I have tried that would previously caused it to over heat has resulted in......nothing......temp guage glued to the half way mark (except when cold, but you get what I mean!)

In total, this has cost me about £1500 with the radiator, water pump, thermostat housing, cooling hoses, reservoir and three res caps being replaced.

She's running great, feels great, can't wait to take her back to Italy after being sidelined for a year!
Wow glad you hadn't left it a few more months or something would have gone bang by the sounds of it probably the belt wrecking your engine
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Old 26-09-2019   #11
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Re: Coolant is boiling!

What a great story. Happy you got it all sorted. Annoying to think you would of had this sorted sooner but purely car you assumed your mechanic did all the replacement of certain parts you would assume they are good. I'm a big believer in name and shame to avoid someone experiencing same issue so I would leave a review and convey your issues across w8tho8t looking like a bitter customer. But glad you got it sorted.
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