Don Terrill’s Speed-Talk

hello, 2005 imp 3.4 with 50 k, problem just started last week, temp reads high and fans will only cycle for a very short time 10/15 sec every 2 min but the gage says 3/4+ hot, when the heater is on it does not cycle, the defrost must be on for a very short cycle 10/15 sec. every couple min. turn on ac and same cycle, checked grounds/changed coolent temp switch/fuses are ok/changed 3 relays/checked coolant/pull temp sensor wire off and reinstall and fans cycle mayby once correctly and then go back to very short rune time again/car runs perfect,heat is great,air is cold, car is clean with no corrosion or rust and is not a frequently washed car,owned since 1 yr old. Fans sound smooth and quiet and are free to the touch all connections look nice and clean also any help is appreciated, no lights or warnings show up on the dash. thanks.

Have you checked the dealership for any bulletins on it?

It could very well be the fan is coming on when the a/c compressor cycles in the defrost mode.It could be due to low refrigerant level or it could actually be perfectly normal.What does it do if left to run without the heater or defrost on? fan cycle normally then?

barnym17 wrote:It could very well be the fan is coming on when the a/c compressor cycles in the defrost mode.It could be due to low refrigerant level or it could actually be perfectly normal.What does it do if left to run without the heater or defrost on? fan cycle normally then?

True, but if the engine temp is higher than it should be fan should run regardless of AC defrost/function.
Possibly, the normal condition needed to run the fan is messed up (measured engine temp) but not the one for AC compressor (high side pressure?).


A lot of newer cars don't turn the fan/s on until 220° or more. Can you scan the data stream and see reported engine temp or coolant fan on/off status?
Does the gauge read normal with highway driving?

I had a few GM cars and yeah the cooling fans can be a problem. On my 2000 Buick Lacross with 165,000 miles I just rig up a switch after cutting the wires, lol. Work just fine, then around 185,000 the odometer went blank, still seem to run fine.

Oh at first the fan relays were changed--took 3 relays, it took care of the problem for a while. Then it got to the point were the fan work only on a/c, was fine until the a/c stop working, that is when I wired a hd switch in--not right but it worked, I did use a fuse--think 30 amp, I just wired up one of the fans, was fine expect in hot summer weather in stop traffic during the day--I tried to stay free of traffic jams on those hot days

The GM dealers will bleed you to death.

I had changed the temp switch with a "new one" and my problem seemed worse, gauge went higher, so I returned that sender and recieved another "new one" , bled the system and all seems well right now , I don't have a scanner tool but perhaps I can send it out to have it scanned, my problem was I thought the fans cycled too fast and my temp gauge was reading higher than normal, I never had any troubles with the system but the gauge read was scaring me, it still cycles for a very short period of time but it ran perfectly today and tonight in local traffic 45 mph, temp looks very steady now, even left it idleing while I went to the grocery store for 15 min and the guage held OK. my thought is the original sender took a crap and the fan cycle just scared me, then when I put the new second sender in the problem seemed worse, third new sender is now working fine, I'll keep ya posted if anything developes, thanks guy's for your help.

All was good until I tried to deliver the vehicle, the temp guage started to rise slightly but I knew it was out of the range that I know as a normal read, I turned off the engine for a min and when I refired it the temp was 50* higher, I shut it off and refired it up a minute later and the guage buried itself, no other problems are present at this point so I am going to say the hell with the read and wait for an overheat situation, car runs perfect through this whole ordeal.

Make sure the cooling system is bled well it sounds like you have an air pocket in it.

check for combustion gases in the cooling system. also when filling disconnect the short hose from above the water pump housing to the pipe near the upper plenum..this will allow air to escape when refilling with coolant and prevent air pockets.

GUYS! You have to scan these newer cars!

Thermostat

mike walsh wrote:GUYS! You have to scan these newer cars!

Yep, it's kind of hard to fix a problem like this without a scanner to see what's actually going on.




Roger
582r10
2 weeks, 2 tickets
runs good

I have bled this car a couple of times, it is not air bound, it does not overheat and I can almost hold the top hose ( it is very warm ) when it is up to temperature, it's not a thermostat as I can feel it cycle with the top hose temperature, right now the temp reads off the scale at 5:00 at running temp and 180 when cold, guage markings are maxed out at 2:00 which is 260 on the dial, this is a guage issue or the computer is sending the wrong signal, I have been on the internet and there are approx 28 hits on the same subject but not one on a reliable repair. I'll keep everyone posted, I'm may send it out to get it scanned.

A quick hit on google shows some info used by megasquirt for the GM ECT thermistor sensor ( http://www.bgsoflex.com/megasquirttherm.html ) . I'm sure there is a posted transfer function somewhere so you could check with a volt/ohm meter and watch the sensor...VOM's are notoriously slow so you might need a scope. However, if the sensor is not bad(you're on your third if I read correctly), you probably have a wiring or ground issue. The computer is basically a dumb device that relies on sensors to tell it what to do.

Bottom line, if the sensor is working correctly(you'll have to verify), you'll have to find what's causing the sensor signal that the ecu is seeing to change. Most likely a ground issue.

hth's
-Carl

p.s. After perusing the megasquirt article a little closer, it seems people use the same sensor for IAT as well as ECT. Off topic but the brass encapsulated ECT sensor should never be used for IAT, it reacts too slow. Again, off topic, I'll post the correct GM sensor and connector for each if anyone is interested. I bring this up because I just saw a Painless EFI harness with the wrong IAT/connector recently. Maybe some think that's ok????

p.p.s. After a further peruse, Bruce posted the transfer function.

Baprace wrote:I have bled this car a couple of times, it is not air bound, it does not overheat and I can almost hold the top hose ( it is very warm ) when it is up to temperature, it's not a thermostat as I can feel it cycle with the top hose temperature, right now the temp reads off the scale at 5:00 at running temp and 180 when cold, guage markings are maxed out at 2:00 which is 260 on the dial, this is a guage issue or the computer is sending the wrong signal, I have been on the internet and there are approx 28 hits on the same subject but not one on a reliable repair. I'll keep everyone posted, I'm may send it out to get it scanned.

First..let me start by saying that,,,everyone on this site,is about a gazillion times smarter than me when it comes to fixing these machines,,,I'm only offering a suggestion,based on experience,,,that being said:I worked as a line tech for GM for 25 years,,,that might make me the MOST dangerous person with a wrench that there is,,anyway,,,during my time there,I constantly had situations identical to this problem,,and,,it's like everyone has said,,,you have to be able to verify the temps by either using a scan tool or a laser temp meter at various locations on the block,,,but in almost 90% of the cases like this,,,it was the Instrument Cluster,,,they were BAD,,,I lost count of the number of clusters I either replaced or sent back to be repaired,,,and 5% were the BCM,,like I said,,,just a suggestion,,but like everyone has said,,no doubt,,a scan tool is going to have to brought into play,,,now,,,I am going to go and get back on my paper and be quiet.