heard today this mod may have caused some head problems with the head warping. has there been any data to support or debunk this.?

Unfortunately not. I've seen a small number of reported cases of head failure when an inline thermostat has been installed. I've also seen many more reports of head failure with no mention of thermostat type. There is insufficient data to draw any statistical conclusions one way or the other.

The problem with trying to mail down whether the inline setup is responsible for head failure is that there are a number of additional variables to consider:
- Where exactly is the thermostat installed in the hose?
- Have you drilled a bypass hole and if so what size and where?
- Is the OE housing intact or gutted?
- If intact what is the failure state of the OE thermostat element?
- If the OE stat is still in place you need to also bear in mind that it's behaviour will likely continue to change as it ages so something that works fine initially may cause problems down the road.

Are you still considering a gutted housing with inline? I'm sure your aware of the other options, they've been discussed plenty.

The inline can cause overheating problems which might or might warp a head. Comments:
1. the OEM CRD tstat is in some sense up-side-down in that when the OEM tstat is in relaxed/closed position coolant flows thru the head/tstat housing/to the viscous heater/to the radiator bypass circuit/and the degas port to the coolant tank is open.
2. when the OEM tstat is tensioned/open it goes down and closes the by pass circuit which forces coolant into the previously mentioned passages AND the radiator.
3. if the OEM tstat fails open or opening too early coolant immediately goes to the radiator and the engine never warms up.

An inline is "ok" for a while if a hole is drilled in the skirt so some coolant always flows to the radiator BUT if the inline fails closed the bypass is kept open and no coolant, other that that thru the skirt hole, flows thru the radiator. This condition especially absent a skirt hole can cause insufficient cooling and coolant overheating.

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Sold to LOST member my 05 Ltd, GDE Stg II turbo + TCM tune, SunCoast TC w. Transgo kit, Steiger window regulators, Samcos, Fumoto valve, 2nd gen filter head with Lub. Spec. bleeder, Hayden clutch & 11 blade fan, inverted spare, P-1 battery, BF Goodrich Long Trail TAs, Etecno1 glow plugs, timing belt at 50K miles/8 yrs

I had a cracked head and was using a inline t-stat at the time.

About a year ago I posted a hasty survey to identify if anyone else had a cracked head while using the inline t-stat.
I think there were only 4 confirmed including myself.
Take that for what it is.

If you ask me, if you want to keep your head from cracking and your valves from breaking, keep the head as cool as possible by ensuring that nothing can restrict coolant flow anywhere in the system.

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U.S. Army Retired

sounds like a catch 22, you can't get there from here. you either run the stock stat and never get above 178* or 130 if the stat failed. or you run the inline which brings the temp to 195 (happy diesel) but comes with some risk. I see some have taken the stat apart and put in a 195 stat, but is the new stat engineered to fail open like the factory.
leave it to Chrysler to create such a mess, damned if you do and dammed if you don't.

IMO, the factory thermostat (when functioning properly) really isn't all that bad. And its a VM Motori design not Chrysler.
Yes, its designed to open at about 176F, but trust me, during the summer time it will have no problem getting up to 190F.
But I live in Florida. Folks who live in colder climates will have a different experience.

And even when I installed the inline 195F and coolant temps were consistently in the 190-200 range, my MPGs did not improve one bit.
With my current weather conditions I'm operating in the 175-190 range and getting 26mpg. And my diesel seems pretty happy.
But like I said, I live in Florida. #floridaman

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U.S. Army Retired

do you still have the inline stat in place? if so how long have you had it in place?

When I purchased my CRD I did not realize my Tstat was starting to fail and it sat at the 1/4 mark except when I was running on the expressway. After reading about the Stant (195F) I put one in and ran it for about 40K miles. The temperature never varied and it sat just below the middle line all the time, summer, winter, idling, running on the highway. When I did my timing belt I replaced the system with a new OEM Tstat. During the 3 seasons up in WI & IL it always seems to run just below the center line, same as the stant. Most of our driving, 90% is on the highway. I have noticed in winter that when below zero it will not reach the center line when on the highway. If you are idling or traveling on surface streets it will sit one line or so below center, probably closer to 176F.

did you have a inline hose tstat?

After replacing my cracked head I gutted the factory thermostat housing and reinstalled my Meziere inline thermostat housing with 195F stant inside.
I have been running like this for almost 2 years now.

The problem comes from having 2 thermostats. You should only need one.
If the factory thermostat opens at 176F and the bypass port closes at the same time, what happens to coolant flow when it hasnt warmed up enough to open the 195F in-hose thermostat?

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U.S. Army Retired

did you take the housing apart to gut it. not sure how the by pass closes but if the factory stat is stuck open ?????????

Yes, I split the housing apart.

The thermostat has two valves on a single piston. When one valve opens the other closes.
If its stuck fully open, the bypass is fully closed.
If it opens too early, the bypass closes early.

So in any case, when using a factory 176 thermostat AND a in-line 195, there will be a point where both the main outlet and the bypass outlet are closed and coolant flow is restricted.

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U.S. Army Retired

so you gut the stat, how does the bypass work then?

There is no bypass valve and therefore the bypass stays open all the time.
With the main outlet being larger, when the thermostat opens then majority of coolant flows out to the radiator.

I dont claim this modification to be the best thing for the CRD. There are better options.
Do your research and choose your own path.

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U.S. Army Retired

thanks, I now have a better understanding of how it works.

Also had a head warp due to inline tstat. Got rid of all that crap and put the HDS on both of my Libby's.

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2006 LTD Bright Silver loaded with all the needed mods, CCV intact.
Proudly supporting CRD vendors, and their development of quality parts and accessories.
Equipped with HDS thermostat, plenty of heat, faster warm-ups, increased fuel mileage.

I guess my fix is halfway between. Have made 2. One for me and one for a friend. Uses Ford contour thermostat housing. Reuses this thermostats bypass port to maintain flow when it hasn't opened and OEM has. Search on here for junkyard thermostat.

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Now have GDE full torque eco tune and eco transmission tune. Used an 02 liberty trans computer for my new trans tune.

I have the Meziere inline in 2 of my CRD's . No problems with either one. I did install a fail open thermostat in each one when I installed them.

I had a Stant thermostat installed inside the hose of my red CRD. The temp would occasionally go to red line when towing in the summer. I used it for three years, but pulled it and put in a new factory thermostat a few months ago (stant also failed open). No head problems.

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My collection of CRD's:
2005 Deep Beryl Green Pearlcoat
2006 Light Khaki Metallic Clearcoat
2006 Inferno Red Crystal Pearlcoat
2006 Midnight Blue Pearlcoat
2006 Gold Limited
2015 Black Ecodiesel
2015 Black Ecodiesel 2

You are really lucky. I didn't even hit red but it cracked my head right inbetween an intake and exhaust valve seat. That was with the mez clamshell and a small hole drilled

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05 CRD: H.D.S2 stat,WW Ironrock trilink&LCA's, OX rear,ARB front, 4.10's, ARB bumper, Suncoast,OME 3.5, JBA UCA,rock rails, Moabs&265/75 Duratracs, GDE tunes ,FFD fan,ARP's, 2 micron fuel, new valves,sasquatch battery tray & grid heater, tensioner relocated
Mech fan, VH & AC delete

Lucky enough to heed our warning, and get rid of the inline tstat before he also has head failure.

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2006 LTD Bright Silver loaded with all the needed mods, CCV intact.
Proudly supporting CRD vendors, and their development of quality parts and accessories.
Equipped with HDS thermostat, plenty of heat, faster warm-ups, increased fuel mileage.