Overheating of newly rebuilt engine

[EmPeEs6]

After my latest rebuild including 10.5:1 high compression pistons I noticed that the engine gets extremely hot, even at idle state and very low load conditions (in spite of one step colder plugs and 30% E85). When driving the cooling system keeps ect between 88-93°C (the average of a long time run was exactly 90°C / 194°F). The engine gets warm very fast and takes an infiite time (several hours with open hood) to cool down again (ok, it's summer but nevertheless this is not acceptable). Because of this the (current) main problem is overheating during driving stops and parking (engine off). I didn't go wot so far nor did I rev past 4.5k rpm, and of course I know that I have to reduce timing and boost in order to take account of the enhanced compression ratio (at least under wot), but what about closed loop and part throttle conditions: is there any general "rule of thumb" for the required adjustments?

[HawkeyeGeoff]

194°F is not far off of what it should normally run. In high summer temps my car is regularly around this area. What do you think it should be? The lowest I really ever see a warm vehicle is around 184°F in cold temps.

Did you replace the thermostat during the engine install? If so it could have been bad before you replaced it.

[EmPeEs6]

Yes, I also replaced the thermostat by a better performing one (from Cosworth). Therefore the average should be slightly lower, although 194°F is still ok for me. Nevertheless the engine becomes really hot, even with respect to 95°F ambient temperature (and still more when the sun is shining). The basic problem is primarily any engine stop (when ect climbs to 230°F and above) - this definitely became worse after the rebuild.

[WetzMS3]

I agree with @HawkeyeGeoff;. The fans aren't supposed to kick on until around 216*F or so. During my commute home daily, my ECT's are usually around 210-214*F most of the drive.

As he said, I'd check your thermostat, but unless we're mis-understanding your issue, I don't think you have an issue.

[HawkeyeGeoff]

Originally Posted by WetzMS3 I agree with @HawkeyeGeoff;. The fans aren't supposed to kick on until around 216*F or so. During my commute home daily, my ECT's are usually around 210-214*F most of the drive. As he said, I'd check your thermostat, but unless we're mis-understanding your issue, I don't think you have an issue.

Oh man. he didn't mention until just recently that his temps climb to about 230°F in stop and go. That is borderline excessive.

I would personally try the fan mod first and have it kick on earlier.
@Funkster777; might have a little more insight on this topic. He has dealt with MS6 overheating before.

[WetzMS3]

Ooooh, yeah 230* is probably no bueno.

Are you sure your fan is kicking on at all? Is the fan shroud in place and in tact? Are there any air pockets in the cooling system possibly? Are you sure the fan relay is not blown? I'd check those things first, then the thermostat. It's likely one of those things.

[EmPeEs6]

Sorry for the confusion:
When driving my ect never climbs beyond 210 °F (fans are working well), but...
if I switch off the engine, even with open hood (and some cruising before the stop) they quickly climb to more than 230 °F. To illustrate: even after 1-2 hours of parking you cannot touch the hot silicone hoses!

[WetzMS3]

Does the fan stay on after shutting down the engine at all? Briefly even.

[EmPeEs6]

Originally Posted by WetzMS3 Does the fan stay on after shutting down the engine at all? Briefly even.

No, it doesn't.

[MD1032]

I believe it's normal for the ECT's to climb after shutting down the engine. My own car does this. My theory is that since the turbo is water cooled, the residual heat after you shut it down rapidly works its way through the coolant system to the ECT sensor after shutdown. For me, the second I fire it back up and the water pump starts flowing, they then drop right back down again very rapidly. I average 200-214°F in stop and go and 178-185°F on the highway.

[tegxsi]

All this sounds normal to me. I would expect ECT to rise after circulation stops on any car.
My garage turns into an oven when I get home from work. I sometimes reach into the hood scoop and touch the TMIC and it's still fairly warm after a few hours.

[cam1391]

In 105° amb. temps I never exceed 190° ect.. it climbs to ~ 200 after shutdown. Ive never noticed the fans running after shutdown.

[HawkeyeGeoff]

Originally Posted by cam1391 In 105° amb. temps I never exceed 190° ect.. it climbs to ~ 200 after shutdown. Ive never noticed the fans running after shutdown.

Mine always run for a bit after shutdown

[WetzMS3]

Originally Posted by EmPeEs6 No, it doesn't.

Originally Posted by HawkeyeGeoff Mine always run for a bit after shutdown

Same here. Mine always runs after shut down for a short period, when it has been running fairly warm. Like others said, I imagine ECT does climbs quite a bit after the fan cuts off.

Quick google search found this link describing how to test the fan control module. I would test that, and replace if needed. (Different issue in that thread, but similar enough for diagnostic purposes)

stock cooling fan turned on and won't shut off!

From what you are describing, I believe the fan should run for a short time after shut down, and is not. Other than that, I'm not sure you've got a big issue. However, the fan not operating after shut down could point towards the beginning of a larger issue.

[EmPeEs6]

Of course it's absolutely normal that the engine bay temperature increases after shutdown, but in my case (!) the rise is a few degrees higher than before (at comparable ambient temps), as well as the average driving ect - in spite of a better thermostat, so I guess that the engine produces significant more (combustion) heat due to the higher compression and wonder how to take care of this fact via the tune...

[WetzMS3]

Originally Posted by EmPeEs6 Of course it's absolutely normal that the engine bay temperature increases after shutdown, but in my case (!) the rise is a few degrees higher than before (at comparable temps), as well as the average driving ect - in spite of a better thermostat, so I guess that the engine produces significant more (combustion) heat due to the higher compression and wonder how to take care of this fact via the tune...

Are you sure that the thermostat you're using is a "better" one? It may be worth swapping in an OEM unit to see if it improves things.

Are your exhaust gas temps showing an increase in temperature as well? Are you experiencing any KR that may signal significantly hotter combustion temps?

[RalliartRsX]

Once the engine is turned off, there is no coolant circulation and there WILL be a temp spike for this very reason. It really is a non issue as the temp at the sensor is the localized temp and not necessarily what the head/block is seeing itself. This will be the case regardless of compression.

The running temps will be slightly higher due to the higher compression, but not more than a few degrees at most and should quickly come back to normally under normal driving conditions.

Also, I would investigate the thermostat again. If you have to go a "cooler" thermostat, you have other issues and this is just a bandaid. The OEM thermostat is set to the temps to allow peak Engine operation efficiency. I would swap another OEM in and go from there.

Also, with the cooling system opened up, another very likely cause is you have one or a several air pockets in the system. Did you bleed the cooling system correctly?? It takes me about 30+ mins of constant run time to bleed my system completely.

[EmPeEs6]

Practically no pt knock so far, and I do not have the possibility to log or monitor egt.
A brand new oem thermostat, which has been installed before, lead to an ect of 201-208°F. The thermostat has been exchanged since the original one (which got me almost the same ect as now) was slightly broken which resulted in a perpetual loss in coolant.

[WetzMS3]

Originally Posted by EmPeEs6 Practically no pt knock so far, and I do not have the possibility to log or monitor egt. A brand new oem thermostat, which has been installed before, lead to an ect of 201-208°F.

So an OEM thermostat resulted in lower ECTs than the Cosworth you are running now?

[EmPeEs6]

Originally Posted by WetzMS3 So an OEM thermostat resulted in lower ECTs than the Cosworth you are running now?

No, the damaged (original) one resulted in similar ect as now, the new oem one resulted in significant higher temps and was replaced by the Cosworth thermostat one day after installation.

[tegxsi]

ECT rise on shutoff because temperatures are equalizing throughout the engine.

From service manual:
Thermostat initial-opening temperature
80-84 °C {176-183 F}
Thermostat full-open temperature
97°C {207 F}

[meicalnissyen]

Originally Posted by EmPeEs6 Of course it's absolutely normal that the engine bay temperature increases after shutdown, but in my case (!) the rise is a few degrees higher than before (at comparable ambient temps), as well as the average driving ect - in spite of a better thermostat, so I guess that the engine produces significant more (combustion) heat due to the higher compression and wonder how to take care of this fact via the tune...

What process did you use to purge air from the cooling system? these things hold air pretty badly. The manual has a bizarre process, I my self cut the small hose going from coolant tank and EGR and put a double ended barb in, I get a lot of air burped quicker by opening that up after any radiator removals

[EmPeEs6]

Today I noticed that the coolant temperature in stop and go city traffic (~196°F) is even lower than during cruising on the highway at mid speed and low load/throttle (208°F). Very strange...

[Tokay444]

Your car isn't overheating and plug temperature and fuel type have not baring on coolant temperature.
/thread.

[EmPeEs6]

Well, the title should rather be something like "coolant gets too hot after engine rebuild", but meanwhile I'm pretty sure that it's solely related to the fact that the airstream during driving currently doesn't have any cooling effect, for whatever reason (the radiator is just 1 year old)...

[RalliartRsX]

Again, did you correctly bleed the coolant system?? You seem to be avoiding the question entirely although it's been asked numerous times by myself and a few others. Even one fairly insignificant air bubble will cause these very effects.

It's almost as if my post is going entirely ignored.........

[SofaKingAwesome]

Half of the newer posts didn't load when I read this the first time. Now I'm just here for the fun.

Also lol at the step colder plugs comment - Dammit Tokay beat me to it.

[WetzMS3]

Originally Posted by RalliartRsX It's almost as if my post is going entirely ignored.........

I know those feels.

[EmPeEs6]

Originally Posted by RalliartRsX Again, did you correctly bleed the coolant system?? You seem to be avoiding the question entirely although it's been asked numerous times by myself and a few others. Even one fairly insignificant air bubble will cause these very effects. It's almost as if my post is going entirely ignored.........

I didn't bleed the system on my own. According to my shop this has been done correctly (with respect to the official/by Mazda recommended procedure), but you may be right...Thank's for this hint!

[patABQ]

I just went through a very tough time bleeding a radiator on another car. Thought I had done it right, but I did not get all the air out. The car ran 1200 miles without going over 200 and then it spiked and overheated. It took most of a day to get all the air out.

Double check as RalliartRsX said.

[mituc]

In bumper to bumper traffic or when the car idles 94-96-100C ECT is common (yeah, Romania is significantly hotter than Germany but even so).

Overheating is above 110C. The fans are supposed to kick in at 104C, and be full on at like 115C and that's when you should start worrying especially if it happens when the car is moving and not idling in 40C weather for like one hour (and even when idling the fans should take care of the heat transfer).
Above like 120C ECT the head can wrap, and that's not fun because the pistons and block can also suffer.

Assuming you're using Mazda FL22 as coolant AND the system is completely burped you should be fine. Eventually see what radiator options you have for the 6MPS, for the 3BK MPS the Koyorad serves me very well (I've seen even 82-83C ECT when cruising in 37C weather).

[RalliartRsX]

I would personally do a once over whatever the shop does (including bleeding the system). These things are notoriously difficult to bleed and you have to have patience when performing the procedure.

The procedure itself is not labor intensive or difficult by any means, but actually removing all trace of air pockets from the system itself is difficult (and when you think you are complete, continue for another 10-15 mins).

I had the same issue with my PDX vehicle and thought I popped a head gasket as coolant temp would follow boost pressure. Turns out I just needed to bleed the system more.

Goodluck!

[Tokay444]

Start worrying when you're actually overheating. As of right now, there is nothing wrong with the temps you are observing, in the conditions you are observing them in.

[EmPeEs6]

Although my engine is not really overheating, 98°C (208°F) ect when cruising at 25°C ambient temperature (77°F) is definitely too high, but meanwhile I'm sure that this is not related to the rebuilt engine but to some cooling system issue.

[patABQ]

Originally Posted by EmPeEs6 Although my engine is not really overheating, 98°C (208°F) ect when cruising at 25°C ambient temperature (77°F) is definitely too high, but meanwhile I'm sure that this is not related to the rebuilt engine but to some cooling system issue.

I agree. First to look at are air in the system and possible stuck thermostat.

[Tokay444]

What Mazda engineer told you that it was too high? It's not even high enough for the fan to kick on ffs.

[Funkster777]

I watch my coolant temps like a Hawk. I had issues with high temps 230 degrees while driving on the highway (last year). The cause was 2 issues.

One, FMIC was limiting air. I messed with the body so air can go into the FMIC and radiator.

Two, the REAL cause of the issue was a bad thermostat. I replaced this with a stock one from Mazda. Issue of high temps went away. I am right about 195 normal operating temperature. Once I shut off the car, the coolant temps rise (as said no coolant is circulating). My fans do come on (I have not done the aftermarket fan modification) after I shut off the car. It took us almost an hour to bleed the system when I filled it, correct @HawkeyeGeoff; No issues again.

I have been driving my car frequently since then (almost daily) and I have had no issues even on warm 90 degree F days.

[mituc]

Originally Posted by EmPeEs6 Although my engine is not really overheating, 98°C (208°F) ect when cruising at 25°C ambient temperature (77°F) is definitely too high, but meanwhile I'm sure that this is not related to the rebuilt engine but to some cooling system issue.

Cruising for how long? After 15-20 minutes of cruising on autobahn at 120-160Kmph/80-100mph after leaving the city traffic you should see the ECT varying between like 86 and 92C (82-88C when the thermostat opens, 92-94C just before it opens). This is just an example.
If you're cruising around town and the speed never exceeds like 60Kmph/40mph and you always have cars in front of you and you eventually stop 1-2-3 minutes at stop lights form time to time then 98C is to be expected.

Bleed the system one more time though just to be sure. Event hough after some time of using the car with the cooling system partially bled you should see the coolant level going low, which is a sign that the air pockets were filled up with coolant and now you need to top up.

[Tokay444]

There is nothing wrong with his cooling system.
He doesn't need to bleed anything.
Does the gauge in the cluster ever move past normal?

[patABQ]

I agree it looks like it is roughly normal. However, I have very recently went through this and all of a sudden went critical - 250 (different car). It only takes a few seconds for piece of mind to squeeze the radiator hose to ensure water flow and see if there is any air coming out to the reservoir.