Engine running hot

[sheetsofsound]

I'm having heat problems and I'm looking for opinions. My previous 7 never ran above the halfway mark on the temp gage. My current 7 runs above half as a matter of course,and goes up to 3/4 when revving above 3000 rpm for any length of time.

Using the 'search' function, I've read and tried the following:
Cleaned the contact on the sensor.
Removed and tested the thermostat.
Changed out the radiator for a new one I had in the garage (don't ask).
Bypassed the heater matrix.
Flushed out the block. When I did this, I found one of the passageways completely blocked with corrosion. Aha! I thought; I've found my trouble. I managed to clear the passageway and run water through, seemingly with no other problems.

When I hooked everything back up, the temperature was actually running higher. I disconnected all hoses and ran water through the block again, in both directions, thinking that maybe some of the rust had blocked up somewhere else. It is now running pretty much as it was before, maybe slightly cooler.

I'm wondering if my water pump is not working properly, perhaps blocked up with some rust? What are the symptoms of a failing water pump? Do they die slowly, or give up their labours in a single spectacular event? What other things might be causing my engine to run hot? I replaced most of the rad hoses, but haven't replaced the lower one yet. It is a bit soft and has a 120V heater fitted about mid-span. (This is Canada, eh?)Or is the corrosion I loosened still hiding somewhere in the recesses of the engine? The car sat in field under a tarp for 10 years and was last driven in 2004, so it has had a long period of inactivity.

Any ideas would be appreciated.

[Hasbeen]

Buy an infrared temperature gauge, & find out exactly what your temperatures are where. They don't cost much, & with one you will know exactly what temperatures are & how much flow you have through the system.

From your post it appears you have dotted most eyes & crossed the Ts as well.

You have bypassed the heater. I assume this means you have a direct feed from the back of the head to the water pump. Is this so?

As the thing comes up to temperature, how quickly does the whole radiator warm?

When my new water pump had the impeller slipping on the shaft some times, & not on others, I found some interesting effects. When it was slipping completely the car would be overheating in 5 kilometers, but the bottom half of the radiator would be cool to touch.

When it was working, the radiator would be very nearly the same temperature all over after a run.

You can get an idea of this by running your hand all over the radiator immediately after stopping the engine after a run. This gives an indication, but is no substitute for knowing the actual temperature by testing with a thermometer.

Hasbeen

[saabfast]

You say 'cleaned the contaqct on the sensor'? It would be better to replace it, they are pretty cheap and do go out of calibration. It may just be giving a high reading.

Alan
Saab 9000 Stg 1 (now passed to son for his family car)
Saab 9000 2.3 FPT Auto (now gone that others might live)
Saab 9000 2.3 LPT Auto (sold on, wish I had it back)
Saab 9-5 2.3 Vector Auto Estate
'81 TR7 DHC

[TR Tony]

I would agree with Alan, change the temperature sender. If that does not fix the issue then follow Hasbeen's suggestions.

Could the heater in the lower hose be causing an obstruction to the flow?

Tony

<font size="1">1981 TR7 FHC Cavalry Blue
1980 TR7V8 DHC Jaguar Regency Red - sadly sold!
1977 TR8 FHC EFI Factory development car Inca Yellow</font id="size1">

[sheetsofsound]

I'll source a temperature sender and replace this weekend; I didn't know they go out of calibration.

Hasbeen: Yes, the back of the head is now routed directly to the water pump. My rebuilt heater matrix will go into the car in a couple of weeks and I'll hook things back up then. I will get a heat gun this weekend as well and check as you suggest. The heat gun has been on my todo list for awhile and I just keep forgetting. Interesting about your impeller slipping. I will check the temp of the rad today if I take the car to work. (My soft top leaks and there's a chance of rain, so, sadly, it may stay in the garage.)

Tony's point is well taken - I will replace the heater hose and check the 120V heater to see how much it restricts things. I would like to keep the heater, as I'm sure it will prove useful if I drive the car through the winter, but if its causing my current trouble it will have to go.

[TR Tony]

The temperature sender works on resistance - if you remove the connector & touch that to a good earth with the ignition on then your gauge should go straight to HOT as there is no resistance. The senders can start to fail & give incorrect resistance readings which in turn gives incorrect gauge readings. My TR8 gauge read very low all the time, having checked out everything else I replaced the sender and all is now normal.

Another thought is it could be that you have a faulty temp gauge. Do you have a spare that you could swap into the cluster to compare?

Tony

<font size="1">1981 TR7 FHC Cavalry Blue
1980 TR7V8 DHC Jaguar Regency Red - sadly sold!
1977 TR8 FHC EFI Factory development car Inca Yellow</font id="size1">

[Maxwell]

Hi - My gauge was swinging wildly between half and full, and usually settled on full. It was the temperature sender, about £8:00. A minute to take the old one out, thirty seconds to screw the new one in. Now it struggles to reach the mid-way point. Voila!

Maxwell [8D]


2.0 TR7 FHC \ Current
1.8 Mazda MX5 \ Current

[FI Spyder]

As mentioned take temp readings with an infrared thermometer at various places under various conditions (various temp readings), record these temps and places so you can compared them and see if they are changing. The temp gauge/sensor is based on a resistance loop so any changing resistance (bad contacts) will cause it to change, not only the wires at the sensor but at the gauge as well (also faulty gauge or sensor although sensors seem more likely to give a problem). Less likely is a break in the wiring loom. So the gauge readings may not be representative of what's going on, hence the use of the infra red therm. Although your engine may not be blocked if it is corroded it will not give you good heat transfer from metal to water. Did you use a rad flush to help clean this out? Although Hasbeen's slipping WP rotor is rare the pumps are pretty reliable being positive drive (no slipping belts) and the only problem they cause is leaking coolant past the seal and out the side of the block. Check the smaller hoses and metal lines for blockage, unlikely the bigger hoses will not likely cause a problem. I like to change the hoses periodically and not wait to have them blow out some where on the side of the road but that's just me.

Rad flush is pretty benign so a friend of mine that has a Spitfire had high temps in his Toyota truck so he flushed the rad with it out with CLR and a lot of crap came out of the ra(although you should be able to rule out the rad you could run it in the engine, then flush). It ran cool ever since. Now CLR is pretty aggressive and you don't want to leave it in too long (ten minutes).

- - -TR7 Spider - - - 1978 Spitfire- - - - 1976 Spitfire - - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra - Yellow TCT

[sheetsofsound]

Alright. I've spent what time I had this weekend trying to get this hot car to run cooler.

I replaced the lower rad hose and checked the inline heater. No restrictions.

I flushed the block using CLR. It produced a little bit of rust and scale, but the water running from the block was clear and the flow seemingly unrestricted.

Filling the cooling system was very slow. I could hear air bubbles as the block was filling for a long time.

Temp gauge shows about the same, moving from just over half at the coolest, to right on 3/4 after some more spirited running. It never climbs above the 3/4 mark.

Got off my butt and got an infrared temp gauge. Measurements taken after 30 minutes showed even heat distribution on the block and head - @170F. Readings on the rad a few minutes after shutting off the engine were different top to bottom by about 20 degrees F. While the engine was running, rad temp top to bottom was about the same.

Tried to replace the temp sender, but had no luck finding one. That's tomorrow's job.

I have another set of gauges, so I'll try hooking up another temp gauge tomorrow as well.

Is 170F about what these cars should be running at?

Any other ideas that I should try?

[Cobber]

I'd consider 170 deg F as running on the cooler side of medium for an emission control spec engine of the 70s onward.
Though by using an I/R temp gun you are measuring the temp of the surface of what you're aiming at, not the coolant itself, which is likely to me hotter by as much as 20-30 deg F which I would consider to the warmer side of medium.

That's not to say the I/R temp gun is a bad thing, no, not at all, it's best used as a comparator to find differences in temp rather than relying on the absolute figures indicated.

What I would be checking is the water pump, as when you rev it the tenp rises which may indicate a slipping impeller that freewheels when the load increases with the higher RPM.


"Keep calm, relax, focus on the problem & PULL THE BLOODY TRIGGER"

80'Triumph TR7, 73'Land Rover (Ford 351. V8),
'89 Ford Fairlane
'98 MG-F, 69'Ford F250.

[Workshop Help]

To check if the thermostat is functioning, point the temperature gun at the top of the thermostat housing. When the engine is at FULL operating temperature, the reading will be 'about' the rating of the thermostat itself.

With your 170 degree reading, I would suspect more previous owner tinkering by his installing a 160 degree thermostat. The usual accepted thermostat used hereabouts is a 180 degree unit. This keeps the combustion temperatures at an acceptable level and prevents failure of the head gasket. The original EPA desired 195 degree thermostats are really only suitable for consistent cold winter driving conditions where a super hot heater is needed.

Mildred Hargis

[sheetsofsound]

I just ran the car and took some readings. The head actually showed a little bit of difference front to back, although not consistently. The rear was around 10 degrees hotter. The rad was showing a difference top to bottom of about 20 degrees.

Mildred: I believe you are right about the thermostat. The thermostat housing was showing about 160F to 165F.

I'm still showing just under 3/4 on my temp gauge. I ordered a new sender and will have it tomorrow. I got the other set of gauges I have out of one of my other cars, so I'll try hooking that up tomorrow; just didn't get that far today.

Other than the sender and temp gauge, I'm not sure what my next steps might be, except the pump.

SOLVED: It was the sender. Just got the new one in and its showing engine temp at just over 1/4 at tickover, and just under 1/2 after a 45 minute run. Thanks all.

[Workshop Help]

Whoa, Hoss! You ain't done yet. Now that you've delved deeply into the cooling system, the next step is to verify the rating of your thermostat. As mentioned above, the 180 degree version is the one to have for long term efficiency and happiness.

There will be those rabid adherents to the famous footed type who will preach the holy words in it's favor. There are also certain heretics avowing the cheaper and easier to find non-footed version will work just fine. In any event, depending on your own moral code, the 180 degree rated thermostat is preferred one to install.

Mildred Hargis

[sheetsofsound]

Dagnabit, Mildred! Alright, alright, ok...

I have two thermostats. When I tested them in water on the stove, the one that's in the car right now opened first and I assumed the second one (which looked older and well-used) was not working as well because it opened later and more slowly. (They both have feet, btw. My morals notwithstanding, on this point I am still a novice and so have not developed strong opinions. Having said that, risking being cast aside as a heretic at this early stage would be a blow, so footed I shall remain.) I now know, of course, that there are different thermostats, so I am assuming that the second one is perhaps rated hotter than the one I have in the car.

I will test the second one again on the stove, this time with a thermometer. If it is the 180 degree model, then I will change it. I am worried about the thermostat housing, as it is apparent that the PO also worried about cooling and changed thermostats a few times and/or fiddled with the housing for some other reason. The housing bolts have been replaced and it feels as if they have been tightened almost to the point of stripping. When I removed them with a torque wrench, they had been tightened to less than 5 ft/lbs. The gasket used was some rubber contraption that had been modified from something else. I have made my own gasket and tightened it back up to less than 5 ft/lbs with no leaks so far, after carefully cleaning off a lot of gasket gunk that had been used previously.

The 180 degree thermostat is preferable to the 160 degree one that I suspect is in the car right now?

[Hasbeen]

Have a good look at the thermostat. I have a couple & they both have a number stamped on them. One is 180, & the other is 80. I'm assuming one is fahrenheit & the other centigrade.

Some time back, a few years, I had to fit a hotter thermostat in our winter, [Scottish summer by comparison], as the car was running just off the low stop on the gauge.

I can't remember what it was with the inferred thermometer, but it was so low I went & bought a new thermometer, as I thought mine must be faulty. It wasn't.

Hasbeen