Mild Overheating, not at idle but at speed !

[neon]

Hello Forum - An unusual pattern of moderate but "stable until it breaks" overheating has started to cause some worry. Unlike most of the threads I have read, which involve overheating at idle or in traffic, my coupe temp gauge goes to about 2/3 the range of the gauge ( see photo) - but well above mid range - and only when driving at typical rpms and while moving. The strange thing is that while idling, the temperature actually comes back to normal range, about at mid range on the scale. I tested the thermostat and it was fine opening at 80 deg C but I replaced it anyway. I drained coolant and it looked relatively clean but since I was under the car without a lift naturally I lost the first 1/2 liter or so - the usual baptism by Prestone. I am about to remove the radiator and send it out for cleaning. The fan coupling " seems " to work ie the fan appears to increase appropriately with engine rpm but I did not do the timing light test described in the blue book. (When "cut off speed" is mentioned is that the rpm at which further increases in engine speed to not give increases in fan rpm ?) The fan is turning at idle even during a cold start. Wondering what the forum thinks about next steps - should I go for the radiator cleaning ? I could replace coolant and check for cold spots on the radiator since I have a surface thermometer, and try the timing light test on the fan ? Or is there a better way to go down the decision tree ? I assume there is no way to test the water pump or can you set up a pressure gauge on the bleeder tap to measure pump pressure ? I did bleed the system Thanks guys ( and gals)

Dana

 

[neon]

Hello Forum - An unusual pattern of moderate but "stable until it breaks" overheating has started to cause some worry. Unlike most of the threads I have read, which involve overheating at idle or in traffic, my coupe temp gauge goes to about 2/3 the range of the gauge ( see photo) - but well above mid range - and only when driving at typical rpms and while moving. The strange thing is that while idling, the temperature actually comes back to normal range, about at mid range on the scale. I tested the thermostat and it was fine opening at 80 deg C but I replaced it anyway. I drained coolant and it looked relatively clean but since I was under the car without a lift naturally I lost the first 1/2 liter or so - the usual baptism by Prestone. I am about to remove the radiator and send it out for cleaning. The fan coupling " seems " to work ie the fan appears to increase appropriately with engine rpm but I did not do the timing light test described in the blue book. (When "cut off speed" is mentioned is that the rpm at which further increases in engine speed to not give increases in fan rpm ?) The fan is turning at idle even during a cold start. Wondering what the forum thinks about next steps - should I go for the radiator cleaning ? I could replace coolant and check for cold spots on the radiator since I have a surface thermometer, and try the timing light test on the fan ? Or is there a better way to go down the decision tree ? I assume there is no way to test the water pump or can you set up a pressure gauge on the bleeder tap to measure pump pressure ? I did bleed the system Thanks guys ( and gals)

Dana

Addendum to above: the temperature drop accross the radiator is about 21 degrees centrigrade, 82 degrees at the inlet and 61 degrees C at the outlet, while the temp gauge is at mid position on the scale.

 

[sfdon]

When the gauge is at 3:00 or less- stick a rolled up newspaper directly into the blades- does the fan stop?

 

[Arde]

When the gauge is at 3:00 or less- stick a rolled up newspaper directly into the blades- does the fan stop?

At idle speed I guess.

BTW, nowadays you may wish the fan to go on and the newspaper stop...

 

[tochi]

Hello Forum - An unusual pattern of moderate but "stable until it breaks" overheating has started to cause some worry. Unlike most of the threads I have read, which involve overheating at idle or in traffic, my coupe temp gauge goes to about 2/3 the range of the gauge ( see photo) - but well above mid range - and only when driving at typical rpms and while moving. The strange thing is that while idling, the temperature actually comes back to normal range, about at mid range on the scale. I tested the thermostat and it was fine opening at 80 deg C but I replaced it anyway. I drained coolant and it looked relatively clean but since I was under the car without a lift naturally I lost the first 1/2 liter or so - the usual baptism by Prestone. I am about to remove the radiator and send it out for cleaning. The fan coupling " seems " to work ie the fan appears to increase appropriately with engine rpm but I did not do the timing light test described in the blue book. (When "cut off speed" is mentioned is that the rpm at which further increases in engine speed to not give increases in fan rpm ?) The fan is turning at idle even during a cold start. Wondering what the forum thinks about next steps - should I go for the radiator cleaning ? I could replace coolant and check for cold spots on the radiator since I have a surface thermometer, and try the timing light test on the fan ? Or is there a better way to go down the decision tree ? I assume there is no way to test the water pump or can you set up a pressure gauge on the bleeder tap to measure pump pressure ? I did bleed the system Thanks guys ( and gals)

Dana

Several things to consider. Preventive maintenance is good, but is it possible the issue is with your temperature sensor or the gauge?

Although you did not mention this, and it is probably only a remote possibility, could there be a problem with your ignition timing (and/or the distributor's vacuum and centrifugal advance mechanisms)? Radiator cap condition? If it is not holding adequate pressure, you may suffer from temperature variations. Finally, you referenced your thermostat. You are most likely aware of this, but the cooling system usually requires bleeding the air from around the thermostat via the bleed screw at the thermostat housing. Some drill a small bleed hole in the thermostat to ensure against this situation. Regarding fan functionality, if your temperature readings are accurate, then the fan would be inconsequential at speed where your reported temp reading is high - versus the normal temperatures experienced at idle.

 

[neon]

When the gauge is at 3:00 or less- stick a rolled up newspaper directly into the blades- does the fan stop?

Don - thanks this suggestion, I will have to try it in about a week as I pulled the radiator last night and will take it to a radiator shop for cleaning. If it does not stop, I assume there can be a fan problem ? Does the " cutoff speed" refer to the rpm at which the fan stops increasing in speed with engine rpm ?

Dana

 

[neon]

Several things to consider. Preventive maintenance is good, but is it possible the issue is with your temperature sensor or the gauge?

Although you did not mention this, and it is probably only a remote possibility, could there be a problem with your ignition timing (and/or the distributor's vacuum and centrifugal advance mechanisms)? Radiator cap condition? If it is not holding adequate pressure, you may suffer from temperature variations. Finally, you referenced your thermostat. You are most likely aware of this, but the cooling system usually requires bleeding the air from around the thermostat via the bleed screw at the thermostat housing. Some drill a small bleed hole in the thermostat to ensure against this situation. Regarding fan functionality, if your temperature readings are accurate, then the fan would be inconsequential at speed where your reported temp reading is high - versus the normal temperatures experienced at idle.

Several things to consider. Preventive maintenance is good, but is it possible the issue is with your temperature sensor or the gauge?

Although you did not mention this, and it is probably only a remote possibility, could there be a problem with your ignition timing (and/or the distributor's vacuum and centrifugal advance mechanisms)? Radiator cap condition? If it is not holding adequate pressure, you may suffer from temperature variations. Finally, you referenced your thermostat. You are most likely aware of this, but the cooling system usually requires bleeding the air from around the thermostat via the bleed screw at the thermostat housing. Some drill a small bleed hole in the thermostat to ensure against this situation. Regarding fan functionality, if your temperature readings are accurate, then the fan would be inconsequential at speed where your reported temp reading is high - versus the normal temperatures experienced at idle.

Tochi - thanks much for your analysis. I did in fact drill a small hole in the thermostat. I understand retarded timing can manifest this way based on my reading of previous threads. I did not check the temperature sender or gauge - is there a way to do this ?

Dana

 

[Dick Steinkamp]

my coupe temp gauge goes to about 2/3 the range of the gauge ( see photo) - but well above mid range - and only when driving at typical rpms and while moving. The strange thing is that while idling, the temperature actually comes back to normal range, about at mid range on the scale.

(my bold added to the above)

While moving how many MPH, in which gear and at what RPM for how long?

Also carb or FI and any mods?

 

[HB Chris]

Hi temp at speed is usually radiator related, it might have blockages.

 

[tochi]

Tochi - thanks much for your analysis. I did in fact drill a small hole in the thermostat. I understand retarded timing can manifest this way based on my reading of previous threads. I did not check the temperature sender or gauge - is there a way to do this ?

Dana

I neglected to mention the possibility of measuring the accuracy of your temp readings via an infared thermometer. Several ways to check temp sensor with an ohmmeter. I do not have the suggested data at hand, but the few times I have suspected a sensor problem - in the field - it has been easier to merely swap for another sensor. If the sensor “seems” problematic, the issue could be as simple as a bad ground/corrosion. A bad ground on the gauge could also account for erratic readings. And, obviously, the wiring connecting the sensor to the gauge could be problematic.

FWIW, there is some prior discussion regarding sensor resistance readings on the forum. E.g., https://e9coupe.com/forum/threads/d-jet-trouble-shooting.28908/page-2#post-230461

One more thing. You did not mention condition of your cooling system, although you plan a considerable amount of R&R. How old is your water pump? Over the years M30 water pumps had numerous impeller variations. Some did not perform as well as others and outward appearance is not necessarily a reliable indicator of internal condition. If the impeller has corroded or lost a vane or two, your pump may move adequate coolant at idle but perhaps may be less-than-adequate at speed.

 

[lip277]

My thoughts...

I had a 2002 for 30 years and never had any cooling issues - never.
A few things I did...
I ran 70/30 ratio (water to AF)
I used WaterWetter (Redline coolant additive).
I made sure my radiator was free of debris (leaves and road junk)
Thermostat and WP working properly.
Fluid full (and properly bled - not a big deal on the M10 in the 2002. A consideration on the M30 in the E9's)

But on my 2800CS, I could not drive the car at all without the temp gage looking like yours does in the pic you have.
I pulled the radiator. Had that redone.
Installed a new WP.
Drained and flushed the coolant. I found the passages in the block were not clear. The coolant passages in the motor were degraded (blocked) from - I presume - the past owners of the car not doing the proper maintenance.
Nothing I could do on that (clearing the engine passages) without getting into some pretty substantial work.

So - I took the opportunity to remove the original 2.8L M30 and have @sfdon put in a 3.5L M90 (with EFI). So, my fixing the cooling issues I had with the car were the start of my huge slippery slope that has now resulted with a totally redone and awesome car - 5 years later... LOL

 

[Arde]

The answer to any problem, an M90 engine. I like that plan.

 

[neon]

(my bold added to the above)

While moving how many MPH, in which gear and at what RPM for how long?

Also carb or FI and any mods?

Dick - it seems to be a function of RPM mostly, 2000 to 3500 rpm, gear 4th or 5th after perhaps 10 minutes of driving from an idling warm up .
The coupe is fuel injected, no mods I am aware of possibly a custom camshaft ( was hypothesized last time I was at a mechanic but conjecture only).

 

[teahead]

Does the temp go down when you turn on the heater?

 

[Stevehose]

Fan belt tight enough?

 

[Dick Steinkamp]

Dick - it seems to be a function of RPM mostly, 2000 to 3500 rpm, gear 4th or 5th after perhaps 10 minutes of driving from an idling warm up .
The coupe is fuel injected, no mods I am aware of possibly a custom camshaft ( was hypothesized last time I was at a mechanic but conjecture only).

Thanks. The only time my 72 bav temp gauge has gotten even slightly above center was when I got lazy and ran in 4th gear at 1500 RPM or so for a distance. It doesn't sound like that might be your issue.

 

[dang]

I'm with Chris on this one. I'd start with the radiator, which you have, since getting hot at speed and not at idle means it's not air flow related. Radiator, coolant flow and then maybe checking for a lean condition, heating up more as you drive at speed. My Chevy truck had similar symptoms and it was worn impeller blades on the water pump.

 

[Drew Gregg]

My thoughts...

I had a 2002 for 30 years and never had any cooling issues - never.
A few things I did...
I ran 70/30 ratio (water to AF)
I used WaterWetter (Redline coolant additive).
I made sure my radiator was free of debris (leaves and road junk)
Thermostat and WP working properly.
Fluid full (and properly bled - not a big deal on the M10 in the 2002. A consideration on the M30 in the E9's)

But on my 2800CS, I could not drive the car at all without the temp gage looking like yours does in the pic you have.
I pulled the radiator. Had that redone.
Installed a new WP.
Drained and flushed the coolant. I found the passages in the block were not clear. The coolant passages in the motor were degraded (blocked) from - I presume - the past owners of the car not doing the proper maintenance.
Nothing I could do on that (clearing the engine passages) without getting into some pretty substantial work.

So - I took the opportunity to remove the original 2.8L M30 and have @sfdon put in a 3.5L M90 (with EFI). So, my fixing the cooling issues I had with the car were the start of my huge slippery slope that has now resulted with a totally redone and awesome car - 5 years later... LOL

The Redline Water Wetter is a fantastic product that really does lower the coolant operating temperature. I have been pulling a 3000 lb boat trailer for over 30 years going to Bass tournaments and other fishing outings in Florida. I have always used a 50/50 antifreeze solution and the bottle of Water Wetter in my tow vehicles--a 2001 X5 3.0 and a Ford Explorer 5.0. I never had an overheating problem. Redline makes good products!!

 

[neon]

Does the temp go down when you turn on the heater?

Does the temp go down when you turn on the heater?

Rob - First time this happened I was freaking out and tried turning on the heater, which didn't seem to make much difference. So to the extent that the heater adds substantIal heat exchange capacity ... maybe points to an explanation other than radiator.

I'm with Chris on this one. I'd start with the radiator, which you have, since getting hot at speed and not at idle means it's not air flow related. Radiator, coolant flow and then maybe checking for a lean condition, heating up more as you drive at speed. My Chevy truck had similar symptoms and it was worn impeller blades on the water pump.

Thanks Dang. The one thing that changed prior to the overheating is that I had a MAP unit rebuild as part of a fuel injection failure as well as a rebuild of the fuel injection trigger unit below the distributor. I changed the points and set the dwell to about 39 degrees at starter motor speed, but I have not checked the timing since changing the points. ( I have trouble finding the timing marks on the crankshaft !) Once I get the radiator cleaned I will retest and from there if no joy, will attempt a water pump replacement. Is there an old school way of testing for a lean mixture, other than a spark plug inspection ? Have not noticed any backfiring. I believe the proper method involves an adjustment at the ECU and measuring exhaust carbon monoxide.

 

[neon]

I neglected to mention the possibility of measuring the accuracy of your temp readings via an infared thermometer. Several ways to check temp sensor with an ohmmeter. I do not have the suggested data at hand, but the few times I have suspected a sensor problem - in the field - it has been easier to merely swap for another sensor. If the sensor “seems” problematic, the issue could be as simple as a bad ground/corrosion. A bad ground on the gauge could also account for erratic readings. And, obviously, the wiring connecting the sensor to the gauge could be problematic.

FWIW, there is some prior discussion regarding sensor resistance readings on the forum. E.g., https://e9coupe.com/forum/threads/d-jet-trouble-shooting.28908/page-2#post-230461

One more thing. You did not mention condition of your cooling system, although you plan a considerable amount of R&R. How old is your water pump? Over the years M30 water pumps had numerous impeller variations. Some did not perform as well as others and outward appearance is not necessarily a reliable indicator of internal condition. If the impeller has corroded or lost a vane or two, your pump may move adequate coolant at idle but perhaps may be less-than-adequate at speed.

No known history on the water pump, appreciate the insight Tochi