Compression ratio and engine heat

[CyFi6]

I have been having overheating problems as some of you know, and i just had a thought. I recently replaced my head gasket on my 7mge a little while ago and had the head machined. I remember now i never checked the head thickness before or after the machine work was done, but i remember very clearly the parts circled in red in this picture (courtesy 7mboost if you don't want me to use this picture let me know) had been skimmed. In other words the head surface was low enough to make flat spots on all these areas off the head surface.

Is that an indication that my head was machined too far? I do not remember what the machinist told me as the amount removed nor is it written down anywhere.

Here are the things done to the cooling system in the past couple months

-New Stone head gasket
-Brand new OEM thermostat
-New OEM upper hose
-New radiator cap
-System flushed and filled with Genuine Toyota Red 50/50
-New radiator
+ Good engine under cover
+Good fan shroud
+ Good water pump-no leaks or play

+cooling system has been pressure tested to 17psi and holds
+ No leaks, no air in the system at all
+ Coolant level stays at the full line after every cool down

After i replaced my stant thermostat with an OEM it helped my temps, but they are still nearing 200 Degrees on a short 10 minuet highway drive at around 70-75 mph (with the ac on full).

I am wondering, can this head that has been machined have increased my compression ratio and therefore caused my engine to create more heat, exceeding my cooling capacity? Im not familiar at all with the effects of increased compression ratio other than detonation can be a product, so any help would be nice.

I have also been running 91 octane in the meantime just for assurance.

Thanks.

 

[benchwarmer]

Did you check your fan clutch?

EDIT: Actually, now that I think about it, is 200 as high as it goes? Normal is around 195 as I recall, 200 really shouldn't be cause for concern.

 

[Wills7MGTE]

IDK what your problem is, I know the vented CF hoods for mk4's can drop temps by as much as 20 to 30 degrees ambient engine bay temp

 

[Poodles]

-Fan clutch
-too many bent fins in the IC/condenser/radiator

Highly doubt it's anything to do with the head. Was the water pump replaced?

 

[CyFi6]

the water pump was not replaced but as mentioned there is no play and no leakage from it. Fan clutch is fine but is being replaced with an oem turbo clutch/fan next week, though this shouldn't matter for freeway temperatures anyways.

I also forgot to add that the condenser and radiator have been removed and there are minimal bent fins and no blockage between the two units.

 

[AJ'S 88NA]

What's your timing set at, and did you time it per TSRM?

 

[Poodles]

OEM waterpump has a stamped impeller, aftermarket is cast and appears that it wouldn't flow as well (not to mention the impeller falling apart or eroding away).

If the fan clutch isn't operating correctly it can cause overheats at any speed (as it did on my car)

 

[sneakypete]

this thread has got me thinking. i just finished with my build, and have the opposite problem. my machinist told me how much material was removed from my head and block (dont have the info with me), but we didnt know how much was removed in a previous rebuilt (previous owner). So just to be safe, i got a 2.0mm MHG, and i think that dropped my compression a bit.
Ive noticed that my coolant temp doesnt get up to operating temps (mech water temp gauge). only change i made to the cooling system during the build was 2 e-fans and aluminum shroud.
Could a drop in compression be the reason my coolant isnt getting to operating temps?

-pete

 

[CyFi6]

this thread has got me thinking. i just finished with my build, and have the opposite problem. my machinist told me how much material was removed from my head and block (dont have the info with me), but we didnt know how much was removed in a previous rebuilt (previous owner). So just to be safe, i got a 2.0mm MHG, and i think that dropped my compression a bit.
Ive noticed that my coolant temp doesnt get up to operating temps (mech water temp gauge). only change i made to the cooling system during the build was 2 e-fans and aluminum shroud.
Could a drop in compression be the reason my coolant isnt getting to operating temps?

-pete

It shouldn't, if you have a well working OEM spec thermostat.

 

[Poodles]

Also depends where the temp sensor is.

 

[sneakypete]

the water temp sender is in the same location it has always been, in the water neck. there could be a problem with the line that goes from the sender to the gauge (mech gauge). since its liquid filled, i might have damaged it by kinking the line
im gonna order a new electric temp gauge and see them
-pete

 

[CyFi6]

There is no water line that goes from the engine to a gauge.. its all electronic

 

[Poodles]

Temp sensor in the same place as the stock one? (it's the one behind the bracket for the PS res.)

If it's not there and on the other side of the t-stat it's not going to be really accurate to what the engine is seeing...

 

[Rennat]

to the OP... if ALL of those areas where 'shaved' looking... then they probably went too far, the one marks on my head are at bottom left, and the bottom right (in your pic)

if anything you RAISED your compression...

and 200 degrees on the highway with the ac on full? whats wrong about that? stock thermostat is 192 degrees...



and what kind of car did that head come from? because the little 'quench' pads are gone... was it the stock head or was it ever ported at one point?

 

[CyFi6]

to the OP... if ALL of those areas where 'shaved' looking... then they probably went too far, the one marks on my head are at bottom left, and the bottom right (in your pic)

if anything you RAISED your compression...

and 200 degrees on the highway with the ac on full? whats wrong about that? stock thermostat is 192 degrees...



and what kind of car did that head come from? because the little 'quench' pads are gone... was it the stock head or was it ever ported at one point?

Thats what i suggested, it increased my compression ratio. I have no idea if there was anything previously done to the head, as far as i knew it was a stock never touched 7mge head with 87k original miles on it. 200 for cruising seems a bit hot, if my thermostat is supposed to begin to open at 190, that means cruising on the highway my cooling system is at max capacity, if i ever see a hill/grade whats it going to do with all that extra heat? The timing right now is set at about 14-15 degrees BTDC on 91 octane fuel.

And yes, my sender for my gauge is right before the thermostat in the water neck, like stock, and i have verified its accuracy with an infrared temp gun.

 

[Tanya]

higher compression = hotter cylinder temperatures.

I was sitting at close to 10:1 in my 6M, but it didn't seem to run any hotter than normal *shrug*

 

[IJ.]

I was just about to jump in and say I don't believe you could machine enough off for it to show as increased engine temps on a car with a correctly functioning cooling system

 

[suprabad]

Not likely you've taken enough off that head to increase compression to the point that it would overheat.
Also, higher compression alone is not going to raise your water temps significantly. However, detonation will, but I don't see the compression getting high enough to cause detonation from surfacing the head a couple of times. If that were the case you'd have other problems like timing plate not fitting, and loose timing belt.

Sounds to me like poodles may have your answer, bad fan clutch. Besides which 200 degrees in the summer going 75 with the air on is within acceptable.

 

[Nick M]

Yes, more compression equals more heat. Heat and pressure go up together.

After i replaced my stant thermostat with an OEM it helped my temps, but they are still nearing 200 Degrees on a short 10 minuet highway drive at around 70-75 mph (with the ac on full).

So what? That is normal. A/C on is everything. And that isn't too hot. Are you going by your stock gauge in the dash?

 

[supraguy@aol]

I also doubt that a shaved head would cause obvious increases in temp. Check fan clutch as mentioned, and also thermostat- it may be sticking closed, which would be the same condition as a bad water pump.
Also- you used a Stone head gasket? Not familiar with them.