Temperature question

[Grandavi]

Not sure if anyone has experienced this before, but here goes...

Last year I had my rad pressure tested and everything checks out find except I have a tiny leak in my heater core (they mark that as 9 hours for remove/install). I am about to have that fixed and then switching from regular "green" coolant to the "red" coolant.

However, today I took the car out for a couple hour cruise with the targa off. On the highway, I was between a Prelude and a Hyundai (tiberon?) and we all just kind of went for it (3 lanes of fun). I had the car ahead of them so I just held off a bit and kept slightly in front of them at 185 kph. After about 3-5 minutes of that, i dropped off and went down to 130 kph. Thats when I looked at the temp gauge. It was right below the red tag at the top of the gauge!

I slowed down to 100 kph (62 mph) in 5th gear at about 2600 RPM and the temp went down to slightly above normal. Drove for about 10 minutes, then pulled over and looked over hoses, the reservoir, etc.. and everything was dry and looked full (although slightly overfull in the reservoir).

What would cause that to jump so damn high? If I keep the car at 120 kph or below 3500 RPM, the temp stays normal. When I go higher, the temp starts to climb. No knocks, rattles/pings, etc.. everything seems perfect, although the oil is down about 1/2 a litre (quart).

ANy ideas? I am wondering if the thermostat did something wonky or the water pump is seizing under high load. (although I would expect a noise)
No warning lights, oil pressure was steady.

[Bru]

I have had good results using Eagle brand (in the green bottle) cooling system sealer.
I have it in the cooling system as a preventative measure. If the leak is in the heater core
you'll have to run the heat to seal it. Test the amout of antifreeze using on of those floating ball testors. Should be atleast 50/50 but not more than 70% antifreeze. Air in the system can cause wierd temperatrue readings also. Check the level under the radiator cap when its cold. It should be liquid right under the cap providing there is enough in the over flow tank when it was hot. Check the hose going from the side of the radiator cap to the over flow tank and under the over flow cap for being plugged up (blow some air and see if it bubbles). Check the hose under the over flow cap for tightness. It needs to go down into the liquid to function properly. The rubber hose here deteriates with age. The radiator cap can be tested at a srevice station or perhaps AutoZone. If its old, replace it. You can test the thermostat in 195F water to see if it opens all the way. The jiggle valve is up on the install. I use silicone to seal the thermostat housing. Be careful tightening the 2 housing bolts. They strip or break off easily.

Have you ever noticed how the rubber radiator hose tends to attack the aluminum housing at both places on the block causing pitting and rot? I solved this problem during my last rebuilt by wire brushing the loose metal rot away and then heating a little with a propane torch it to further flake off anything that wasn't solid. Next I mixed up some fresh JB weld from new tubes and smeared on a thin layer. After it hardened overnight it was just like a new surface, smooth and solid. Now the chemicals in the rubber hose can't attack the aluminum because the JB weld protects it.

[Grandavi]

Excellent tips. I replaced the coolant line that runs to the turbo last year, maybe that is the issue. I could have an air pocket. I am getting the system flushed/filled so that might clear it up. That hose burst on me last summer and I lost most of my antifreeze on the road (fun).

I am not sure I want to try the sealant for the heater core, strictly because of the age of the car (88 MKIII). I am thinking that if I replace the hoses to and from along with recoring it, that will just stop any issues from arising for the next 5-10 years (or more). I currently get a greasy "fog" on my windshield if I put the temp to 24 deg and you can smell coolant. It is probably only the valve that is leaking, but like I said.. its a 22 year old car, so probably not a bad idea just to recore it. I dont mind putting coin into the car. Its my last one if it lives as long as I do. The wife can have the newer vehicles. This is my baby. : )